AudioCircle
Audio/Video Gear and Systems => The Vintage Circle => Topic started by: Bill Thomas on 26 Jun 2009, 09:03 pm
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June 26th, 2009 - Update: "Sometimes You Choose Your Projects - Sometimes THEY Choose YOU!"
Sorry it has taken so long to get back to posting these "Rebuild Chronicles", but sometimes "life" has a way of getting in the way of our original plans. But I AM back with our "Second Dose" of "Fine Tuning." The saga of this particular FM-3 tuner has more twists and turns than the Paris Sewer System.
Allow me to introduce you to our "rebuild candidate" in all its radiant glory. In truth, it really did look like a VERY nice tuner. But looks can be deceiving. Let's go through the photos of the tuner in "pre-rebuild" condition.
Here's a frontal shot that shows a VERY nice face plate and very pretty knobs:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SkTpYqyVkNI/AAAAAAAAAuc/r350D7RERaM/s720/Matthew%20Perks%20-%20FM-3%20-%20front%20shot.JPG)
No dings or dents. All the lettering is nicely intact. Even the tuning indicator "window" is in great condition (other than the addition of LOTS of my oily fingerprints). Here's a "view from the top" with the cover off:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkTqkhyQwDI/AAAAAAAAAus/bNRptChF84U/s640/Matthew%20Perks%20-%20FM-3%20-%20top%20chassis%20shot.JPG)
Looks pretty nice, doesn't it? This particular tuner has been the subject of a previous "restoration" and there is a LOT of good that has been done. For one thing, the two 10K 2 Watt resistors on the IF board have already been replaced with 10K 3 Watt parts, mounted slightly "off the board" for better heat dissipation. Here's a picture:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkTpYoNEGII/AAAAAAAAAug/1k_ecGRKDww/s720/Matthew%20Perks%20-%20FM-3%20-%20IF%20resistors%20shot.JPG)
More importantly, this particular tuner has been retrofitted with the "Berning Mod" PEC replacements on the Multiplex board. Take a look at the result:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkTpYZ49KZI/AAAAAAAAAuU/q6bkYxMoPTI/s640/Matthew%20Perks%20-%20FM-3%20-%20Berning%20mods%20shot.JPG)
Also, the main coupling capacitors have also been replaced with more modern "film" capacitors. Here are the two Output capacitors on the Multiplex board:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SkTyTkB51jI/AAAAAAAAAuw/F8k8IbNpVO0/s720/Matthew%20Perks%20-%20FM-3%20-%20Output%20capacitors%20shot.JPG)
The two coupling capacitors on the IF board have also been replaced with new "film" capacitors as well, see?:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SkTyT8lyiAI/AAAAAAAAAu0/YM80lppySts/s640/Matthew%20Perks%20-%20FM-3%20-%20Interstage%20capacitors%20shot.JPG)
Pretty nice, huh? In other words, by all outside appearances, this tuner has been properly "updated" to improve the sound quality and reliability. The owner of this tuner LOVES how it sounds... or at least, how it SOUNDED. But (and ain't there ALWAYS a "but..."), as it turned out, initial "looks" have been VERY deceiving!
MANY months ago, I received this particular tuner for a rather simple repair. The symptom was an OBVIOUS one. It hummed like crazy. In fact, all you could HEAR was a VERY loud hum. It's the classic case of a totally failed quad capacitor. Since there are no suitable replacements being manufactured in the United States, there are only a few options available for Dynaco FM-3 owners with a failed quad capacitor. The *closest to stock* option is to use an "Authenticap" replacement capacitor from Germany. The last time I checked, this option runs about $57.00, so it isn't the "cheapest" alternative. There *used* to be another option. Zack at Vibroworld *used* to custom make replacements, but Zack has been "unavailable" for the past year or so. As it turned out, I had ONE of his custom replacements available in my "stash of new parts" so I used it. Here's a picture of the result:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SkTpY_Sw7JI/AAAAAAAAAuk/yJahwNIBTz4/s512/Matthew%20Perks%20-%20FM-3%20-%20quad%20cap%20shot.JPG)
This solved the hum problem. I dutifully operated the tuner for several days "on the bench" and gave it a "touch-up" alignment. After a few more days of listening, I packed it up and returned it to the owner. Case closed, right? Not *quite*...
After the tuner was reinstalled into its wood case, the owner was able to enjoy it for a couple of days. He was VERY happy with how it sounded. Then, things turned sour.
As he was listening, the tuner started drifting off-station and suddenly, it ceased to function at all. He returned the tuner to me for further troubleshooting.
Of course, when the tuner arrived here, it once again operated properly. Everything continued to look good for MANY days until suddenly, it simply "went away" again. Turning it off for even a few minutes would allow it to cool a bit and begin working again. New tubes did nothing. Inspection of the circuit boards revealed nothing. Hitting the individual components with "cooling spray" revealed nothing. This went on for weeks!
FINALLY, after poking, prodding, bending, pushing, cooling and heating parts, boards and anything ELSE I could think of, I located the *teensiest* break of one circuit trace *under* one of the tiny eyelets on the RF board. It was absolutely invisible to the naked eye. I attempted to repair the "discontinuity" with a bit of solder, which *worked*, but to be honest, I wasn't satisfied with this being a "proper" repair. It is NEVER a good idea to rely only upon a "solder bridge" to "fix" a bad circuit board trace.
I replaced the RF board. Fortunately, I have quite a few FM-3 "parts donors" available. But I *certainly* didn't want to just stick in an RF board with 40 year old parts and call it a day. Who knows what component was "on its last legs" and ready to fail at a moment's notice? I made a valiant attempt to rebuild the replacement RF board.
As we have discussed previously, Dynaco spared EVERY expense when bringing these tuners to market. The original circuit boards are EXTREMELY easy to damage beyond repair. Sometimes you can get lucky and manage to strip the parts off a board without damaging the circuit traces. Yeah, and *sometimes* you can hit the Powerball Jackpot - the odds are about the same. Here's a picture of TWO RF boards from donor tuners:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SkUySOe3jqI/AAAAAAAAAx0/dasjXQTSOpo/s512/FM-3%20RF%20boards%20from%20donors%20-%20no%20good.JPG)
You'll notice that BOTH boards are now useless! Using the lowest heat possible, traces STILL lifted from the substrate - and the RF board is LESS susceptible to damage than the other two boards in an FM-3 because it is a fiberglass board, while the other two boards have a phenolic substrate!
Meanwhile, something strange was going on with the tuner I was attempting to repair. While trying to remove the tuning capacitor from the original defective board, it was taking a LOT more heat to get the solder to melt! During the previous "restoration" a well-intentioned person decided to add silver-bearing solder to each and every solder joint on ALL of the printed circuit boards! As it turned out, this apparently caused most of the *mysterious* problems with the printed circuit boards!
My BEST guess is that the previous person who worked on the tuner simply added a bit of silver-bearing solder to each connection without removing the existing solder. Since the mixture of regular solder mixed with silver-bearing solder was unpredictable, the final result turned out to be unpredictable as well. Some solder joints wound up quite solid. Others apparently developed problems due to different rates of expansion and contraction of the solder mixtures. I can't SWEAR this is the problem, but it's my best guess as to why this tuner wound up developing NEW problems while just "burning-in" on the bench. It's either that, or the Great Norse Gods of electronic repair simply HATE me! Either way, we now had a BIG problem!
We'll begin to cover the solution to this problem in our next update. (Some of you may already guess where this is heading, but don't get TOO far ahead of me here.) The solution just *might* wind up being beneficial for ALL FM-3 enthusiasts! Don't touch that dial, there's a LOT more to come soon!
Sincerely,
Bill Thomas
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Fascinating, Bill! Keep 'em coming!
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June 27th, 2009 - Update: "The Good, The Bad and The UGLY!"
We've seen the GOOD; the overall cosmetic condition of our rebuild candidate. We've discovered the BAD; the overall electrical condition of our rebuild candidate. Now, let's take a look at something truly UGLY - namely, one of my many "parts donors." In fact, it was the source for one of the two RF boards I showed you in the last "installment." I won't bother you with the cosmetic condition of the face plate, knobs and the like. Let's just "cut to the chase" and take a look at the "guts" of our donor. Here's a picture of the underside of the donor's chassis:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkVpTwouIEI/AAAAAAAAA0o/IeBO7y0tGSs/s576/FM-3%20-%20Donor%20Tuner.JPG)
Compare that picture with a picture of the underside of our current rebuild candidate:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SkTpYVRfS5I/AAAAAAAAAuY/8EY6fS_n2d0/s576/Matthew%20Perks%20-%20FM-3%20-%20bottom%20chassis%20shot.JPG)
Take a closer look at some of the donor unit's "features", like scorched and melted insulation:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SkVooWRigII/AAAAAAAAAz0/WHvhSF2mTzk/s512/FM-3%20-%20Donor%20Tuner%20-%20More%20Bad%20wiring.JPG)
And, of course, the added "feature" of using masking tape to insulate some of those scorched wires:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkVooPd1iII/AAAAAAAAAzs/gdTc2sEeDKs/s512/FM-3%20-%20Donor%20Tuner%20-%20Bad%20IF%20section%20wiring.JPG)
That is just WRONG in so MANY ways. Ahh, but there's MUCH more. Take a look at the amount of solder used on the RF board:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SkVpTZD-ZoI/AAAAAAAAAz8/_xW7RAaVegY/s512/FM-3%20-%20Donor%20Tuner%20-%20RF%20section%20-%20poor%20solderingJPG.jpg)
And take a look at the general "build quality" around the terminal strip:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkVpTz8O0NI/AAAAAAAAA0E/QmpJdKrVB3s/s512/FM-3%20-%20Donor%20Tuner%20-%20terminal%20strip%20area.JPG)
The soldering and wiring of the multiplex board also leaves a LOT to be desired. Take a look:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SkVooVX6IzI/AAAAAAAAAzw/9jp_sHVO1-A/s512/FM-3%20-%20Donor%20Tuner%20-%20Bad%20Multiplex%20section%20wiring.JPG)
It should be pretty easy to see why I decided to make this tuner a "parts donor." Sadly, it was not able to yield any usable printed circuit boards. This puts us in a pretty tough spot. On one hand, we have a nice looking tuner that is TOTALLY unreliable. On the other hand, we have LOTS of "donor units" that won't yield any decent circuit boards. Rather than "waste" any more tuners in the *hope* that we might salvage a 40 year old circuit board, I decided to take a different approach.
Here's an initial picture of our "different approach":
(http://lh6.ggpht.com/_Xp_4nF2BnZE/Si7FfRBqQEI/AAAAAAAAAmE/bYE3jttQs2E/s400/PC-7%20-%20New%20Board%20%28undrilled%29.JPG)
This is the first *successful* copy of a PC-7 RF board. Notice that there are no holes in it - yet. But here's a picture after about an hour of careful "hole drilling" using a small drill press:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SjKUxkYHNLI/AAAAAAAAAmo/9jAJq43kYSE/s400/PC-7%20-%20New%20Board%20%28drilled-alternate%29.JPG)
The GOOD thing is, this board has NO eyelets on it! This alone should help increase out reliability factor a LOT!
There are BOUND to be lots of questions about how to actually reproduce these boards and I hope to cover that topic in a future update. Suffice it to say that it took several weeks and LOTS of "trial and error" to FINALLY get the PC-7 RF board to turn out properly. But now that we HAVE, let's "stuff" the board with parts.
There is a proper "order" in "stuffing parts" onto a new PC board. It's pretty simple really, you start with the lowest profile parts and work up to the bigger ones. Since the 1/2 Watt resistors are the parts with the smallest "profile", they go first like this:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SkVusRoetKI/AAAAAAAAA0g/NCQ9UksBNoo/s400/FM-3%20-%20NEW%20PC-7%20RF%20board%20-%20initial%20assembly%20-%20resistors..JPG)
Next, we move up to the 1 Watt resistors and the small coil "chokes" like this:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SkVusK4LybI/AAAAAAAAA0Y/gSxejL7HM7o/s400/FM-3%20-%20NEW%20PC-7%20RF%20board%20-%20initial%20assembly%20-%20more%20resistors%20and%20chokes..JPG)
And we continue adding parts until we wind up with this:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SkVusBf43mI/AAAAAAAAA0U/LvIadwEpk1k/s320/FM-3%20-%20NEW%20PC-7%20RF%20board%20-%20completed%20assembly%20-%20top..JPG)
And here's a picture of the solder side of the circuit board:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkVpUALdguI/AAAAAAAAA0M/L5aRDcLqlWk/s400/FM-3%20-%20NEW%20PC-7%20RF%20board%20-%20completed%20assembly%20-%20bottom.JPG)
Notice that we didn't just "glom" on a bunch of solder. We used just enough to surround each wire connection with a nice, clean, shiny joint. But this is only one-third of the "Circuit Board Story." In our *next* update, we'll take a look at the other two boards. Yes, we're making new IF and multiplex decoder boards as well and you'll get to see the results for yourself VERY soon. Until then, don't touch that dial - you might *miss* something!
Sincerely,
Bill Thomas
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Wow, great write up! Very inspirational.
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June 30th, 2009 - Update: "Mistakes Were Made!"
Deciding to make new Printed Circuit Boards for an FM-3 tuner was NOT an "easy" decision, but in the case of our current "rebuild candidate" it was the ONLY decision IF we wanted to wind up with a *reliable* FM-3 tuner. Due to the high heat necessary to melt the silver-bearing solder, the existing boards were CERTAIN to shed their circuit traces if we had attempted to strip them and "start over" with new parts and solder.
Since it has been quite a while since the last time I laid out and etched any circuit boards, it was time to "revisit" the board-making process. This took several weeks of board-making attempts until a reliable, repeatable method was assured. There were MANY "oops" moments along the way. I thought you might like to see a few attempts that DIDN'T "make the cut."
Let's start out with our PC-7 RF board. You've seen the raw, etched board we DID accept. (Here's a picture to "refresh your memory"):
(http://lh6.ggpht.com/_Xp_4nF2BnZE/Si7FfRBqQEI/AAAAAAAAAmE/bYE3jttQs2E/s400/PC-7%20-%20New%20Board%20%28undrilled%29.JPG)
Now, here's a picture of one of the boards that WASN'T acceptable:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/Skk_T3-LjlI/AAAAAAAAA5w/sva1jbD3dlA/s400/Rejected%20PC-7%20board.JPG)
What happened? Well, this particular board was made using a photo-sensitized PC board and three copies of the circuit pattern printed with a laser printer on mylar film. It is necessary to use three copies in order to increase the "density" of the black areas on the mylar film. But for this method to be even *remotely* successful, the three mylar sheets must be aligned PERFECTLY! That was NOT the case here. Notice that the circuit traces are rather poorly defined, or a bit "bloated" causing them to fail to maintain acceptable separation from other traces. Let's look a little closer.
Here is a closeup of a few circuit traces on one of the replacement capacitor boards produced from Sheldon Stokes' artwork. (Sheldon's artwork is absolutely WONDERFUL. It was my attempt at making a circuit board from it that was flawed.) Here's an example of the BIGGEST "trouble spot" on this rejected board:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/Skk_TiuudJI/AAAAAAAAA5k/uO3ZvQpRQuY/s400/Rejected%20FM-3%20cap%20board.JPG)
Notice that the tiny holes for the components are "football shaped" rather than round. This is due to the overlaid films failing to maintain registration. But the MUCH bigger problem has to do with the three "pads" on the top of the picture. The two pads on the right side are *supposed* to be joined together. But the third pad (the one on the left side of the three) is ABSOLUTELY not supposed to connect to the other two. The mis-registration was the culprit. How much mis-registration was there? Well, the EASIEST way to show you is this:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/Skk_TtCa9ZI/AAAAAAAAA5s/whSqUIkVWPg/s720/Rejected%20PC-12%20board.JPG)
If the registration had been correct, the printing would be clean, clear and crisp. Not even CLOSE! And there are other problems as well. Here's another reason this board was rejected:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/Skk_TUKiKKI/AAAAAAAAA5g/7eQlREdMIdM/s400/Rejected%20FM-3%20cap%20board%20-%20smutz.JPG)
There was apparently some "garbage" included with our photo-sensitized board. Instead of nice, clean traces; we have traces that are *almost* non-continuous because of "hairs" on the surface of the photo-resist. NOT good!
There are LOTS of boards I *can't* show you because they were TOTAL failures. When they were dropped into the photo-resist developer, ALL of the photo resist wound up being dissolved in the solution. The result? A totally copper-covered board with NO "trace" of a pattern anywhere. There were NUMEROUS "experiments" with different light sources, different exposure timings and different temperatures for the solutions. In the end, there were simply too many "variables" involved to get good, REPEATABLE results using photo-sensitized boards. It's ONE thing if you are a commercial board manufacturer and have complete control over ALL of these variables. It's quite another "thing" if you are churning out individual circuit boards in a garage. Please realize, the photo-exposure method is capable of turning out circuit traces with the BEST definition of any method available. But in order for that to happen, the planets (and the mylar sheets) must all be in PERFECT alignment EVERY time.
Fortunately, there is another, more "forgiving" method that is capable of turning out REALLY good boards on a repeatable basis. It doesn't depend upon light to expose a pre-sensitized board. It doesn't require "developing" in a carefully temperature-controlled developing solution. All it takes is a laser printer, the "correct" paper and a household iron. If a mistake is made and a trace doesn't get completely deposited on the copper-clad board, it can be "repaired" using cheap nail polish, OR the board can be completely cleaned and you can try it all again. Unfortunately, my camera was "on the fritz" when these boards were made so I don't have pictures of the "iron-on method", but perhaps we can cover that process during another rebuild.
The boards we wound up using were made utilizing this "iron-on" method. While not always "perfect", it wound up being a much more "forgiving" process, when all was said and done.
In our next update, we'll take a look at the PC-8MX board and the PC-12 board - top and bottom. THAT update is right around the corner. Stay tuned!
Sincerely,
Bill Thomas
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June 30th, 2009 - Update Two: "Are You Bored With Boards Yet?"
I promised that we'd be taking a look at the PC-8MX IF board and the PC-12 Multiplex board in this update, so here we go!
First, let's look at a "comparison shot" showing an original "harvested" PC-8MX IF board above one of our NEW IF boards:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SjlOvC5DjDI/AAAAAAAAAms/eW0wzR5Z86Y/s720/PC-8MX%20comparison%20shot.JPG)
The original board has a LOT of damage due to "lifted traces" when I attempted to strip the old parts off the board. The original Dynaco board used a phenolic substrate. The new board was made using FR-4 fiberglass board material - DEFINITELY more reliable.
But the PROOF is "in the stuffing." Here's a picture of the PC-8MX board at about 95% completion:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkmQ0546JEI/AAAAAAAAA54/ensfG9yA5Ws/s720/PC-8MX%20-%20almost%20complete.JPG)
There are really only four more parts to be added to the board. There are the two 10 K power resistors for the first two IF stages. The Left one goes here:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkmQ04EWZfI/AAAAAAAAA6A/USPk_OOKN1I/s576/PC-8MX%20-%20First%2010K%20resistor%20location.JPG)
And the Right one goes here:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SkmSKaqDkpI/AAAAAAAAA6k/PirUNzWZavo/s720/PC-8MX%20-%20Second%2010K%20resistor%20location.JPG)
Next, we will need to add the Discriminator Transformer. It will be mounted later after the board is installed in the chassis. Here's where it will go when the time comes to add it:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SkmQ04zpc8I/AAAAAAAAA58/0gjQXOIqIFA/s400/PC-8MX%20-%20Discriminator%20Transformer%20location.JPG)
The only other part remaining to be added is the little PEC module for the IF board. It goes here:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkmR2LZJfUI/AAAAAAAAA6U/DbEdYP5ez-A/s640/PC-8MX%20-%20PEC%20location.JPG)
Let's take a moment to talk about those little PEC modules. They were produced by Centralab and when you stop to think about it, they were actually the forerunners of today's integrated circuits. No, they didn't include any "active" elements, but they DID integrate several individual components onto a single substrate. Then the whole "shootin' match" was dipped and coated with a ceramic material. I'm betting that Dynaco used them because it would be a simple matter to use a different PEC module for different FM de-emphasis time constants for different parts of the world. I'm not sure if they ever actually DID that, but they *could* have.
Dynaco wasn't the only manufacturer to use them. They were VERY common in Philco televisions. (The "Predicta" televisions had several of them.) Other manufacturers used them as well. It was a pretty clever idea whose time had not *quite* come. For one thing, the capacitors contained in a PEC module are basically the same as ceramic disc capacitors. OK for RF and Bypass applications, but not the greatest for audio coupling. On top of that, they weren't *that* reliable over the long haul. As anyone who has attempted to restore a Philco "Predicta" will tell you, one of the most common tasks is replacing the PEC modules with discrete parts.
The PEC module Dynaco used on the IF board was such a simple circuit (two resistors and one little capacitor), one wonders why they bothered to use one there at all. Knowing how Dynaco operated, I'll bet they wound up saving a penny or two over the cost of three discrete parts. While I DO have a few original Centralab PEC modules in NOS condition, we'll save those for someone who REALLY wants to hear an FM-3 in absolutely "bone-stock" condition. We'll make up a replacement using higher-quality, discrete parts.
So, let's look a little closer at the IF board. Here's a picture of the left-hand third of the board:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SkmQ1BaoIeI/AAAAAAAAA6I/Fjz7htdBKPE/s720/PC-8MX%20-%20Left%20third.JPG)
All passive components are new parts. EVERY resistor was carefully selected to be within 1% of the target value. Plate resistors are metal-films for lowest noise. Carbon-composition resistors are used where audio passes through them and for a few other minor areas where currents are low. Allen-Bradley carbon-composition resistors were used for highest reliability. (A-B's are the "creme de la creme" of carbon-composition resistors!) Most of the critical plate resistors are Vishay/Dales. ALL of the resistors are either "dead-on" or within 1% of the specified value - even the carbon-comps. The coils are originals that have been re-used.
Now, here's a picture of the Middle-third of the IF board:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SkmR2NZ8p6I/AAAAAAAAA6Q/riM2xthiDRk/s720/PC-8MX%20-%20Middle%20third.JPG)
And finally, here's a shot of the Right-hand third of the IF board:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SkmR2f-m_hI/AAAAAAAAA6c/RCmLKGIryYk/s720/PC-8MX%20-%20Right%20third.JPG)
There are a few rather important parts changes we need to mention in this picture. Notice the two little mica capacitors? They replace two 47 pF NPO disc capacitors that were originally used here. These capacitors are used to develop the audio signal from the Output of the Discriminator Transformer. Since these little beasties are actually critical to the task of generating audio from the FM signal, micas just *might* be a better choice as far as audio quality is concerned.
Also notice the "Orange Drop" capacitor. It is the capacitor used to couple the audio signal from the center point of those two mica capacitors and into the grid of the 12AX7. Originally, it was a ceramic disc capacitor. The "Orange Drop" *should* be MUCH kinder to the audio signal delivered to the 12AX7. We'll add the discriminator transformer after the board is mounted to the chassis.
In case anyone is curious, here is the lineup of pictures showing the "solder-side" of the PC board. First, the left-hand third:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SkmQ1M7sa4I/AAAAAAAAA6E/IpuOEyittFY/s720/PC-8MX%20-%20Left%20third%20-%20solder%20side.JPG)
Now the middle of the board:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SkmR17aIcnI/AAAAAAAAA6M/1PIWDjEz1-E/s720/PC-8MX%20-%20Middle%20third%20-%20solder%20side.JPG)
And finally, the Right-hand third of the IF board:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkmR2Cp1VqI/AAAAAAAAA6Y/JdDRD3HkTtc/s720/PC-8MX%20-%20Right%20third%20-%20solder%20side.JPG)
The long component leads that remain will eventually be trimmed once all wires have been connected to the board. Although the pictures don't make it *completely* evident, all solder joints are nicely clean and shiny. It's interesting to note that the copper on these boards was also clean and shiny when we started, but has oxidized *ever-so-slightly* over the past week. The photos actually make the oxidation look a lot worse than it really is. Of course, *eventually* the boards will have a "darker" look due to copper oxidation, but it doesn't affect the operation of the boards in ANY way.
Let's hold off covering the PC-12 Multiplex board until our next update. We have a few "extra" things to cover on that board and I have a cat that is BEGGING me to "hit the sack" so she can get some "snuggle time" before the sun comes up. Our next update is coming later in the day. Until then, Stay Tuned!
Sincerely,
Bill Thomas
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June 30th, 2009 - Update Three: "Let's Play TWO! (Channels, that is.)"
Let's take a look at the PC-12 Multiplex board. (Dynaco calls it a "Multiplex Integrator for the FM-1" which is how things all started back when Stereo FM was brand new.) The Dynaco folks were a clever bunch. Back when the design for the FM-1 tuner was being "ironed out", they KNEW Stereo FM was coming, but they didn't know EXACTLY which system would wind up being selected. As a result, they planned the FM-1 with space reserved for the FMX multiplex integrator OR for the inclusion of a little Power Amplifier that turned the FM-1 tuner into a self-contained tube-type FM Radio. All the user needed to add was a nice speaker. Unfortunately, this little tube-type amplifier increased the heat factor inside the tuner from a heater into a blast furnace.
Fortunately, the "FMX Multiplex Integrator" only added two small signal tubes; a 6BL8 and a second 12AX7. While this *did* add a *little* more heat, it was NOTHING compared with a couple of 6BQ5's that were used in the amplifier module!
Here's a picture of the "circuit trace side" of an original multiplex integrator board:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/Si7FfLnvXGI/AAAAAAAAAl8/rhjBrS7lI-8/s400/PC-12%20-%20Stock%20Board.JPG)
Nothin' fancy going on here, just a "normal" Printed Circuit board on a phenolic substrate. Now, here's a look at my first (successful) attempt at a replacement board:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/Si7FfXOwszI/AAAAAAAAAmA/yhSz-nrXwcM/s320/PC-12%20-%20NEW%20Board%20-%20%28undrilled%29.JPG)
Notice that the board has not yet been drilled in this picture. The circuit traces are clean and crisp. Everything *looks* ok - *almost.* There is actually one *teensy* little error in the circuit trace layout. It's not a "deal-breaker" and it HAS been corrected on the Master Artwork, but see if you can spot the problem.
Rather than bore you with a bunch of "gradual" assembly pictures, let's just "cut to the chase." Here's a picture of the board with about 90% of the components installed:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SkmSmXl3PYI/AAAAAAAAA6o/Xn1Cv1vc304/s400/PC-12%20-%20almost%20complete.JPG)
We still have one transformer to install and the two Output coupling capacitors to add. THEN we have to add two PEC replacement boards. Other than that, this board is DONE!
The transformer will be installed here:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SkmSmhyvooI/AAAAAAAAA6w/BnpzTbWy3W4/s400/PC-12%20-%20transformer%20needed.JPG)
The PEC replacement circuit boards will be installed here:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SkmSmdMLijI/AAAAAAAAA6s/NjBX9JHz2Rs/s720/PC-12%20-%20PEC%20modules%20needed.JPG)
If you'll remember, the tuner we started out working on already had two PEC replacement boards installed. But they were also soldered together with silver-bearing solder. Rather than deal with that, let's just replace those little PEC boards. As a bonus, the replacement boards are a little smaller. Here's a picture showing you the size of these boards:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SkmSmgn8ZzI/AAAAAAAAA64/8vXO28IGWt0/s400/PEC%20modules%20-%20size%20comparison.JPG)
If you'll look closely, you'll see that the board on the left has slightly less "definition" than the board on the right. It's nothing that will affect the operation of the completed boards, but the board on the left was *slightly* mis-registered, causing the lettering to be a little "thicker." No big deal.
These boards were made from artwork graciously provided by Sheldon Stokes - the S.D.S. of SDS Labs. You can make your own boards using the same artwork. Just visit Sheldon's website at: www.quadesl.com (http://www.quadesl.com) to find out more, as well as other free artwork for capacitor boards and MUCH more. Thanks, Sheldon!
These little PEC modules make it a SNAP to perform the "Berning Mod" on your FM-3 tuner. But if you don't feel like etching and drilling your own boards, you can make perfectly acceptable substitutes using standard perforated boards. These little circuit boards just give things a bit more of a "polished" appearance.
According to Dynaco, we're now about halfway through our build of an FM-3 tuner. There's a LOT of fun yet to go. In our next "update", we'll begin the actual mechanical assembly of the main chassis. Stay tuned!
Sincerely,
Bill Thomas
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July 1st, 2009 - Update: "Hey, Man! Dig Them PECS!!"
(Sorry! I couldn't resist.) Let's finish our look at the PEC modules. These little babies have a LOT to do with the ultimate sound quality of an FM-3 tuner. They also make it possible to change the de-emphasis time-constants for different Countries. MOST Countries around the world use a 50 microsecond de-emphasis circuit. Here in the United States, we use a 75 microsecond de-emphasis circuit. It is important to use the correct circuit in order to provide flat audio response at the Output jacks.
We are using the "Berning Mod" PEC circuit to improve upon the original ceramic PEC modules. (They were really nothing to write home about and they didn't really provide flat audio response.) The tuner we are rebuilding had replacement PEC boards installed, but these are a *bit* smaller. I also like to use Polystyrene caps for the three 510 pF capacitors when possible. Of course, dipped micas will work just FINE as well. Here's a picture of a completed, "stuffed" PEC module:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SkvgIa0NBtI/AAAAAAAAA7A/b8MShh6npgY/s400/PEC%20-%20closeup%20-%20uncovered.JPG)
While I would probably *normally* use Allen-Bradley carbon-composition resistors for the 10K resistors, these modules are in a rather high heat area of the tuner, so these Corning Metal Films will *probably* work out a bit better.
Since I tend to "err on the side of caution", I prefer to cover these little modules with some BIG heat-shrink. Here's what happens:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SkvgIe3ZuuI/AAAAAAAAA68/Cukcjmkwti4/s640/PECS%20-%20uncovered%20and%20covered.JPG)
I just feel better when there's a bit of insulation over these little boards - *just* "in case..." To get a nice, even "shrink", I just use an electric stove. You can control the amount of heat by raising, or lowering, the part over the eye. While the tubing is still hot, I just "pinch" the sides and cut off the excess. While not *quite* as thin as an original Centralab PEC, it's not THAT much thicker either. Still, when two of these are installed, they DO have to "rub against each other" a bit. The heat-shrink covering just adds a little *insurance.*
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SkvgIdHvX8I/AAAAAAAAA7E/z9j5eJqvbTU/s512/PEC%20-%20closeup%20-%20covered.JPG)
We'll be replacing a different PEC module in our next update, plus we'll take a look at part of the assembly and final wiring of our tuner. Hopefully, we'll secure the blessings of Audio as WELL as the blessings of Liberty before the 4th of July Weekend is over!
Enjoy the Holiday, Friends, but NEVER forget the reason why we celebrate it! The "Grand Experiment" may be a bit "tarnished" in places, but She still shines a beacon of Hope and Liberty around the world. (That's ONE reason why some folks HATE us. They don't "cotton" to the idea very much.)
Be Safe! Stay Well! Stay Tuned! MUCH more to come!
Sincerely,
Bill Thomas
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Great work, Bill.
Independence Day was great and for this Vet, I'll never forget!
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Hi Bill,
I wonder about your choice of Styrene capacitors in those PEC modules. Correct me if I am wrong, but I thought that the Polystyrene caps were more temp. sensitive than mica types. I would have suggested micas for a very hot running tube unit.
Regards,
Frank Van Alstine
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Hi, Frank!
I was concerned a bit at first as well. You are absolutely correct that the Polystyrenes are more sensitive to heat. But after some "real world testing" in four different tuners, they seem to be able to "take the heat" without a problem (so far). Perhaps it's that heat-shrink covering that provides a bit of "insulation" from the direct heat, but of course, *eventually* everything inside that little "oven" winds up at an elevated temperature. Still, at THIS point, they seem to be able to tolerate it without incident.
Then again, sometimes I DO like to "live on the edge." They sure do wind up sounding very sweet in this application.
Sincerely,
Bill Thomas
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Monday, July 6th, 2009 - Update: "Mr. Clean - At Your Service!"
Let's face it, cleanliness *may* be next to Godliness, but when it comes to a 49 year-old FM tuner, cleanliness is next to IMPOSSIBLE. This is especially true regarding the cad-plated chassis parts. "Who cares what the *insides* look like", you say? *I* care! And YOU should too!
There are a LOT of parallels between restoring a piece of electronic equipment and restoring a classic car. When you rebuild an engine, the *first* thing you do is tear it down and clean the whole thing THOROUGHLY! Each and every part MUST be completely clean in order to assess the condition of the part. The same thing holds true for our good ol' FM-3 here. After almost 50 years of service, our once *pristine* metal parts have taken on a certain "patina", making it pretty easy to tell this thing has *quite* a few miles on it. Since we're tearing this one down ALL the way, (just like an engine in a classic car), let's give it the old "College Try" and see what some elbow-grease and a few "magical potions" can do. As it turns out, quite a LOT!
Here's a picture of the main chassis after a fairly thorough cleaning:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SlLxhQDZ_vI/AAAAAAAABA0/jwJ7_Kw9JMU/s720/Main%20Chassis%20-%20cleaned.JPG)
The front of it looks like this:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlLxhmXqewI/AAAAAAAABA4/7_wrs8jJnFk/s720/Main%20Chassis%20-%20cleaned%20-%20front%20shot.JPG)
And the back looks like this:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SlLxhuAjbFI/AAAAAAAABA8/mmljNPCw7Kg/s720/Main%20Chassis%20-%20cleaned%20-%20rear%20shot.JPG)
No, it's not PERFECTLY clean (although I actually went back and cleaned all the metal parts again after these photos were taken), but the small discolorations are cosmetic only and won't affect the longevity of the finished tuner. For the *most* part, it's pretty-durned clean! (And *shiny* too!)
Likewise, the cover for the tuning capacitor was cleaned and shined up a bit, see?
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SlLxh7MsbGI/AAAAAAAABBE/WrXdCwWONyg/s400/Tuning%20Capacitor%20cover%20-%20cleaned.JPG)
And then there's the part nobody sees during actual operation of the tuner - the Front Panel:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SlLxhgJbn1I/AAAAAAAABBA/yMc5JeHcQK8/s720/Front%20Panel%20-%20cleaned.JPG)
And finally, the Bottom Cover:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SlLx9AUtAQI/AAAAAAAABBI/96c2leSrIPk/s640/Bottom%20cover%20-%20cleaned.JPG)
You'll notice that the cleanup of the bottom cover isn't *perfect* either, but you kinda have to make a choice here: Do you want a *perfectly clean and shiny bottom cover? Or do you want to keep the original Dynaco lettering as "intact" as possible. I tend to operate according to the "Hippocratic Oath" - "First, do no harm." Since this particular tuner will be slid into a wood cabinet, the bottom cover won't be *generally* visible. The minor imperfections that remain shouldn't detract from the overall enjoyment of the tuner TOO much. And I *prefer* to keep the lettering on the Bottom Cover as close to "original condition" as possible, so a "gentle" cleanup was the way to go here.
Loretta Lynn once sang: "Love Is the Foundation", but the BEST foundation for an FM-3 tuner is a CLEAN foundation. If the goal is to wind up with a tuner that will serve up GOOD music for another lifetime, it just makes sense to spend the time to clean up the original metal parts NOW while the tuner is completely apart.
Coming up next? We're going to populate our "clean foundation" with some circuit boards - NEW circuit boards. Stay tuned. The fun is just beginning!
Sincerely,
Bill Thomas
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Tuesday, July 7th, 2009 - Update: "Gettin' Down To Business!"
So far, we have quite a collection of restored and new parts. NOW, it's time to DO something with them! We'll be working with these parts during the next phase of our build:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SlMDtsonjpI/AAAAAAAABBM/A4JbauCJkGI/s512/Initial%20Mechanical%20Assembly%20-%20parts.JPG)
Actually, there are a few more to go along with it, but this is basically where it all begins.
Dynaco's construction manuals are some of the BEST in the industry. If you follow them carefully, you'll *probably* be rewarded with a completed unit that *works* the first time you turn it on. The late Bob Tucker is responsible for the outstanding order of construction. (Bob was also the co-designer of the Stereo 70, along with the late Ed Laurent, Dynaco's chief design engineer.) Since we are using a few "non-stock" parts or assemblies, we will be deviating *slightly* from the usual order of construction. Nothing *major*, just a few small changes in order to make the whole process go more smoothly, or to improve the final result.
The initial mechanical assembly simply mounts the small parts on the chassis. On the front of the unit, we mount the new Power Switch:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlMDtqSJamI/AAAAAAAABBQ/EiMiJksYEqc/s720/Initial%20Mechanical%20Assembly%20-%20First%20Stage.JPG)
Make certain the switch is centered in the rectangular opening before tightening the two screws. If your original Power Switch is in good condition, you can re-use it. If not, a suitable replacement is available at the nearest Radio Shack. The original switch features tapped mounting holes so no nuts or lock washers are required. The Radio Shack replacement *will* require two lock washers and two 4-40 nuts. (We're using the Radio Shack replacement here.)
Next, we'll install the small parts on the rear of the main chassis like this:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SlMDt1b7mhI/AAAAAAAABBU/Ebsc8bMJQQs/s640/Initial%20Mechanical%20Assembly%20-%20First%20Stage%20-%20rear%20shot.JPG)
Again, make certain all parts are centered in their cutouts before completely tightening the screws. Since the rear of the chassis is usually quite visible, it pays to make it look nice.
Now, install the two small rubber grommets underneath the chassis. Although the manual tells us to install the large rubber grommet on the rear of the chassis, we'll put that "on-hold" until a bit later in the build. Here's a picture of the under-side of our chassis:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SlMDuEtmJyI/AAAAAAAABBY/WWhuYp65jiY/s576/Initial%20Mechanical%20Assembly%20-%20First%20Stage%20-%20bottom%20shot.JPG)
So far, so good. Now, it's on to the most *critical* part of the assembly process - the main tuning capacitor.
In the original attempt to simply repair the existing tuner, it was discovered that the tuning capacitor wasn't all it was "cracked up to be." This required "harvesting" a good one from a suitable donor. Since this is an absolutely CRITICAL component, take some time to properly evaluate the condition of the part.
Before we go ahead and commit to a "harvested" capacitor, we want to make SURE it isn't completely worn out. The first step in evaluating the condition of the capacitor is to grasp the larger "outside shaft" and attempt to wiggle it. If there is any appreciable "play", either side-to-side, or up-and-down, look for another donor. Any appreciable play will cause the plates of the capacitor to move. Any movement of the plates (other than when YOU turn the shaft), will cause the tuning to shift - sometimes a LOT! Rather than waste time dealing with a problem like that, select your donor *carefully* for best results. The capacitor we will be using is in FINE condition - mechanically speaking.
Next, turn the capacitor shaft clockwise until the plates of the rotor are visible. Are any of them bent or "tweaked" in some way? If so, look for another donor. It will be nearly IMPOSSIBLE to achieve proper dial tracking if the plates of the rotor are bent.
Now, turn the shaft of the capacitor counter-clockwise until the plates are fully meshed with the stationary plates. Here's what you *should* see:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SlMFO9sLQXI/AAAAAAAABBg/LB4fIatLYcU/s576/Tuning%20Capacitor%20-%20even%20mesh%20of%20plates.JPG)
Notice that the plates are basically "in the middle" between the stator plates. This is the desired condition we were hoping for. When you are evaluating a tuning capacitor, check to see if any of the plates touch or rub against any of the stationary plates. If they do, toss it and look for another donor.
If the potential donor checks out, check the action of the planetary drive mechanism. Turn the small "inside shaft" and observe the "feel" of the mechanism. If it turns smoothly without a "gravelly" feel, or without "dead spots" where no movement occurs, you *should* be fine.
Once you have determined that the capacitor is a suitable replacement for your old damaged one, clean the ball bearings at the front and rear of the capacitor to remove the old grease. Avoid getting any solvent into the planetary drive mechanism. Once the old grease is gone, lubricate the ball bearings with conductive grease. The grease I use is available at W. W. Grainger. Here's a picture:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SVP2C-BNubI/AAAAAAAAAWE/KVOX7qESYo8/s400/FM-3%20-%20Secret%20Sauce%20Tuning%20Capacitor%20Grease.JPG)
This *teensy* little tube of grease costs a little over $27.00! Good thing you don't need to use much of it. Why does it cost so much? Because it contains silver - that's what makes it conductive.
Here's a shot of the rear ball bearings after re-lubrication:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SlMFPCotLlI/AAAAAAAABBk/kKghDib1A9k/s640/Tuning%20Capacitor%20-%20rear%20bearings%20-%20re-lubed.JPG)
And here's a shot of the front bearings:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlMFPPizMDI/AAAAAAAABBo/oDx_pkm2UM8/s512/Tuning%20Capacitor%20-%20front%20bearings%20and%20intermediate%20fingers%20-%20re-lubed.JPG)
Notice that a little conductive grease has also been added to the copper spring contacts that make contact with the shaft of the rotor. We want to keep the resistance at the contact points as low as possible. This stuff is pretty messy and it can get all over everything. As with Brylcreem, "A little 'dab" will do ya!"
Before attempting to install the capacitor, make certain the rotor is fully meshed with the stator plates. This will offer a little *extra* protection to make sure we don't inadvertently bend the plates of the rotor.
Once the tuning capacitor is fully cleaned and re-lubricated, line it up with the slots on the RF board like this:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlMFPc3KDAI/AAAAAAAABBs/V2SCcgEFPJk/s400/Tuning%20Capacitor%20-%20ready%20to%20install%20on%20RF%20board.JPG)
Now, *carefully* insert the tabs on the bottom of the capacitor into the slots on the PC-7 RF board. From the top, this is how it should look:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SlMHG2_yT6I/AAAAAAAABB0/7NTC9neoKdE/s400/Tuning%20Capacitor%20-%20mounted%20on%20RF%20board.JPG)
Here's what it looks like from underneath:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlMHHKurtwI/AAAAAAAABB4/794NlVZwYg4/s400/Tuning%20Capacitor%20-%20mounted%20on%20RF%20board%20-%20bottom%20shot.JPG)
Do NOT solder the capacitor tabs to the circuit traces at this stage. We'll do that after we make SURE the physical alignment of the capacitor is "on target."
Now, mount the PC-7 RF board (along with the tuning capacitor) onto the chassis. The PC-7 F board is mounted using 4-40 hardware and the tuning capacitor studs are mounted using 6-32 hardware. Do NOT tighten ANYTHING yet. Keep it all loose so you can properly position the shaft of the tuning capacitor. Here's a picture:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlMFPXdK_TI/AAAAAAAABBw/OB1u7YtojiY/s400/Tuning%20Capacitor%20and%20RF%20board%20-%20loose%20assembly.JPG)
By leaving the mounting hardware loose, you can *slightly* adjust the position of the tuning capacitor shaft. How can you tell if it's correct? Simple! Place the front panel on the front of the chassis. Make certain the three mounting holes line up properly, or temporarily attach the front plate to the front of the chassis. When properly aligned, the tuning capacitor shaft should be centered in the hole on the front panel. You can be *slightly* off, but anything more than about 1 mm is cause for concern. This is a CRUCIAL step. Make SURE the shaft winds up VERY close to the center of the hole in the front panel. You may notice that the shaft position changes slightly as you tighten down the capacitor's mounting nuts. If so, try again until you are satisfied there will be no "rubbing" or mis-alignment of the tuning capacitor shaft.
We'll continue our assembly in the next update. Stay tuned!
Sincerely,
Bill Thomas
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Tuesday, July 7th, 2009 - Update Two: "More Mechanical Assembly!"
I really can't stress the importance of making SURE the tuning capacitor shaft winds up properly aligned. TAKE the time NOW to get it right and you'll save MANY hours later trying to "correct" it. Once you're SURE it is correct, you can install the PC-8MX IF board assembly. (Fortunately, there is no need to "critically align" THIS board.) But, before I get off my "soapbox" here, take a look at two pictures. The first one shows the tuning capacitor/RF board combination *loosely* assembled to the chassis. The second shows the final alignment, as well as the addition of the IF board to the chassis. Here's the first picture:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlMFPXdK_TI/AAAAAAAABBw/OB1u7YtojiY/s400/Tuning%20Capacitor%20and%20RF%20board%20-%20loose%20assembly.JPG)
Notice that the tuning capacitor shaft is actually "left of center" in relation to the chassis cutout for the tuning dial. Now take a look at the final alignment:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlMHHvQRVuI/AAAAAAAABCE/s_jR_3Tzk1E/s720/RF%20and%20IF%20boards%20mounted%20-%20three-quarter%20shot.JPG)
Perhaps this angle makes the shift a bit clearer:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SlMHHW-FP4I/AAAAAAAABCA/SIjIFnvGz2A/s512/RF%20and%20IF%20boards%20mounted.JPG)
This places the center of the tuning shaft about 1/2 mm to the left of the center of the hole in the front panel - well within "engineering accuracy" in this case. This will insure that the tuning knob won't scrape against the tuning window and that the tuning knob will be parallel to the face plate, when all is said and done.
Here's a picture of the installed PC-7 RF board from below the chassis:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlMJKKsXGFI/AAAAAAAABCM/RQotfcYnehQ/s400/Tuning%20Capacitor%20and%20RF%20board%20-%20loose%20assembly%20-%20bottom%20shot.JPG)
After installing the IF board, mount the PC-12 Multiplex Integrator board like this:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SlMJKhmqT_I/AAAAAAAABCU/RzpufgI_3qA/s512/RF%20-%20IF%20and%20MPX%20boards%20mounted.JPG)
At this point, we would *normally* be mounting the can capacitor, but we're using a different "solution" to the can capacitor, namely: a copy of Sheldon Stokes' FM-3 capacitor board. As a result, we had to "modify" the mounting of the tube socket for the 6V4/EZ80 rectifier tube in order to add two standoffs, front and rear, above the tube socket mounting "ears." Here's a picture:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlMJLB-X9ZI/AAAAAAAABCc/kUG_tUtdwzE/s400/rectifier%20socket%20with%20standoffs.JPG)
Of course, we'll need something to provide the various Voltages throughout the tuner. That calls for a PA509 Power Transformer to supply the "juice.":
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SlMLMrULkRI/AAAAAAAABCo/xMlu52hw6Kk/s512/Boards%20and%20Power%20Transformer%20mounted.JPG)
Now we can add the Tuning Capacitor Cover and the third standoff, as well as the capacitor board, like this:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SlMLNLZFc9I/AAAAAAAABC4/W15hjpxkvkU/s512/Capacitor%20Board%20and%20Tuning%20Capacitor%20Cover%20mounted.JPG)
That little capacitor board is a real "life saver." There is only ONE can capacitor that *I* know of being produced anywhere in the world, and THAT one has to be imported from Germany. But there are a couple of additional "benefits" in using the capacitor board. First, those 5 Watt 500 Ohm resistors are able to dissipate the heat they produce a little easier, since they aren't trapped beneath the chassis. Second, if a "section" of the filter capacitor were to fail, you *could* replace the individual section with new parts. (OK, not a BIG advantage, but Jack Benny would find "the cheap solution" simply *THRILLING*, right?)
When you mount the Tuning Capacitor Cover, there are a few things to check. Make SURE the wire from C8 (the little ceramic trimmer) doesn't touch the cover. Ours is close, but far enough away for comfort, see?:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SlMLMlvPf0I/AAAAAAAABCs/RAkWRU0cMwo/s400/Tuning%20Capacitor%20cover%20-%20no%20short%20at%20C8.JPG)
Also, make SURE the shield "leg" of the Tuning Capacitor Cover is properly seated against the tab for the first IF transformer on PC-7. Also make certain the shield doesn't touch the little temperature compensating capacitor C7:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SlMLM_Zzd-I/AAAAAAAABCw/KUjP7UQu_50/s400/Tuning%20Capacitor%20cover%20-%20no%20short%20at%20C7.JPG)
While you're at it, make SURE that little tubular capacitor DOES touch the tube socket for the 6AT8A mixer/oscillator tube. THIS IS IMPORTANT TO MINIMIZE DRIFT! The capacitor should *also* lie against the PC-7 board itself. Take a look from the top:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SlMLM84pU8I/AAAAAAAABC0/dkrz_-jDnaQ/s512/C7%20detail.JPG)
Well, we've made a LOT of progress! It's actually beginning to look like a real tuner! But we have a LOT more "fun" in store. Next up: "We're Gonna Get Wired!" Stick around. There's MUCH more to come. Don't touch that dial just yet!
Sincerely,
Bill Thomas
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Wonderful write up, thanks for taking the time to do all this.
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Thursday, July 9th, 2009 - Update: "One Last PEC and Some Deviant Behavior!"
Before we get down to the final wiring of the tuner, we have a few "odds & ends" to look at.
I mentioned earlier that we were going to replace the stock PEC module on the IF board with higher quality discrete parts. Since there are only three components needed to build this little replacement for the PEC, rather than slow our project down with a printed circuit board, I decided to just build it on standard "perf board" from Radio Shack. Here's a picture of the board prior to covering it with some heat-shrink tubing:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SlbKRVg8sPI/AAAAAAAABEM/MbcyFTs6mLo/s400/Small%20PEC%20module.JPG)
The other two components are 22K resistors and they are actually located behind the 510 pF capacitor, so they aren't visible in this photo. Here's a picture of the solder side of the board:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlbKRnP2EAI/AAAAAAAABEQ/I7sXXSbENzc/s400/Small%20PEC%20module%20-%20solder%20side.JPG)
The next step is to cover the module with heat shrink tubing and shrink it. Cut a piece of tubing that is 1 1/2 times the length of the module and cut out the holes for the three connecting wires like this:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SlbKRzyFYNI/AAAAAAAABEU/Hue-lmxuO8w/s720/Small%20PEC%20module%20and%20heat-shrink.JPG)
Slide the little module into the heat shrink tubing and crank up a burner on the electric stove. Using long-nose pliers, hold the module over the eye of the stove until the tubing shrinks down over the board. While the tubing is still hot, pinch the two ends of the tubing and then cut off the excess tubing. One side of mine actually folded over, but that really makes no difference. Take a look:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SlbKSDbDBEI/AAAAAAAABEY/sxObsP6_pH8/s400/Small%20PEC%20module%20-%20completed.JPG)
We'll solder all the PEC modules in during the "final assembly" stage of the build, but before we ge to THAT stage, we have a bit of "pre-wiring" to do. THAT brings us to my "Deviant Behavior."
I mentioned earlier that there would be a *few* "deviations" from the instructions in Bob Tucker's Construction Manual. Bob's instructions tell us to pre-wire only three wires on the EMM801 tube socket, V-8. The rest of the wires are soldered to the IF board and are connected to the EMM801 socket during "final assembly." Trouble is, it's REALLY *cramped* around that tube socket. Attempting to solder five more wires on AFTER the socket is mounted to the front panel is no fun at all! So, instead of using that method, I wire all eight wires on the socket of V-8 and cover the socket lugs with small heat-shrink tubing. It REALLY makes a much "neater" job possible. Here's a close-up picture:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SlbLUQoCaiI/AAAAAAAABEg/wCxWaxa8s-Y/s400/EMM801%20socket%20-%20installed%20-%20closeup.JPG)
I just like the added "insurance" of the heat-shrink tubing, plus it LOOKS nice too.
One other thing you might notice: While the manual calls for black and green wires for the filament connections, I'm using white and brown wires. These are the colors Dynaco used when they wired them at the factory, so I decided to "follow in their footsteps. (It makes troubleshooting easier too.) Here's a picture of the installed socket with all the associated wires:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SlbKSWZi5VI/AAAAAAAABEc/SptnxosnSyA/s512/EMM801%20socket%20-%20pre-wired%20and%20installed.JPG)
Before we can wire the main chassis, we have one final "sub-assembly" to pre-wire: The "Stereomatic" Volume Control. We'll tackle THAT little project in our next update, coming VERY soon. Until then, stay tuned!
Sincerely,
Bill Thomas
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July 17th, 2009 - Update: "Some Sub-assembly Required"
The folks at Dynaco were pretty smart when they organized the assembly instructions for the FM-3 tuner. There are basically five sub-assemblies that must be put together before you wire them all together on the main chassis. First, you assemble the three printed circuit boards. Next, you pre-wire the socket for the EMM801 tuning indicator and install it on the front panel. The final sub-assembly is the "Stereomatic" Volume Control. Take a look:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SmDBOVCQmLI/AAAAAAAABGc/95H1hBFNgWU/s400/Stereomatic%20Volume%20Control%20-%20prewired%20-%20overall.JPG)
Not exactly "rocket science", is it? But we're making a small modification to the original plans. We're replacing the Output Wiring with shielded wires, rather than using twisted wires. It's not a BIG deal, actually, but it requires us to ground the two shield (or "drain") wires at the potentiometer. Here's a closeup shot of the wiring:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SmDBOhKcakI/AAAAAAAABGg/cLkw65hoAgQ/s400/Stereomatic%20Volume%20Control%20-%20prewired%20-%20potentiometer%20wiring%20closeup.JPG)
The shield (or drain) wires from the two shielded wires are covered with white heat-shrink tubing. The signal grounds are small black wires and the "hot" wires are small red wires. It is important to note that the shields are ONLY connected at this end. The actual grounding of the audio output section on the PC-12 multiplex board comes from the two small black signal ground wires here at the potentiometer. Ground is provided to these two points by the larger black wire connected to the front section (on the left side of the image) of the potentiometer. This wire will eventually be connected to the main audio ground point on the PC-8MX IF board when we assemble the front panel to the chassis. Here's a picture from the top of the control to help you get a better look at the overall layout:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SmDBO1IIYlI/AAAAAAAABGk/uBPCynFMfiY/s512/Stereomatic%20Volume%20Control%20-%20prewired%20-%20wiring%20closeup.JPG)
The trio of red, black and green wires comes from the PEC module Outputs. The two red wires connected to the switch will connect to the Output of the 38 kHz transformer. When the switch is closed, these two wires eliminate any "spurious remnants" from the stereo demodulator's L-R signal. In "Stereo" mode, we want those "remnants" to show up, but in Mono operation, they can be a source of noise and improper Monaural operation. The two shielded wires carry the Output signal from the Volume Control back to the last 12AX7 stage on the multiplex board. Since these wires have to pass near two tubes that have AC on the filaments, shielding the wires will reduce the chance of any hum pickup. If you're rebuilding a tuner, don't go crazy about this part. The twisted wires used in a stock tuner seem to work just fine. I just like to shield longer runs (like this one) in order to provide a little additional "insurance" against hum pickup. Here's another view of the completed assembly from the front:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SmDBOL3lPrI/AAAAAAAABGY/kQD7B9Q9Cp0/s512/Stereomatic%20Volume%20Control%20-%20prewired%20-%20head-on.JPG)
The trio of wires on the left will actually route behind the slide switch and down to the PC-12 circuit board. The rest of the wires are in the general position they will have when the control is finally installed.
This means all of our sub-assemblies are now finished! All we have left is "bringing them together" on the Main Chassis. We'll cover part of that process in our next update, coming up later tonight. Until then, Stay Tuned!
Sincerely,
Bill Thomas
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I wish I had the patience to do this kind of work. Wonderful job, just wonderful!..... 8)
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July 20th, 2009 - Update: "Let's Get It On!"
OK, so Marvin Gaye *wasn't* referring to an FM-3 when he sang that song, but it's about time we get our FM-3 project completed. When last we left our (soon to be) faithful tuner, we had completed all the sub-assemblies. Now, it's time to put it all together!
If you're restoring an FM-3 tuner of your own, I STRONGLY recommend that you THOROUGHLY read Frank Van Alstine's article "Keeping the Dyna FM-3 Working" located at: http://www.avahifi.com/root/audio_basics/1990-11_fm3_keep_working.htm (http://www.avahifi.com/root/audio_basics/1990-11_fm3_keep_working.htm). This article contains more truly useful information than you will find ANYWHERE else on the web. It also contains a few VERY important "suggestions" that can help improve the operation and reliability of your FM-3. We're about to look at one of those "suggestions" in further detail.
WARNING: Before you follow this "suggestion", it is CRUCIAL that your tuning capacitor be properly positioned. Check it CAREFULLY because you will not have a chance to move it at all once the next step is completed. We're talking about making SURE the shaft of the tuning capacitor is centered in the opening of the front panel. If it isn't, FIX IT NOW!
Once you are ABSOLUTELY sure the tuning capacitor shaft is centered in the front panel opening, it's time to drag out that old soldering GUN you've had tucked away for a long time. You're going to need a LOT more heat than a soldering "pencil" can provide.
Here's the deal: "Grounding" can be a real issue in an FM-3 tuner. As your tuner ages, the quality of the grounding connections can suffer. Circuit boards that *used* to be well grounded can develop "less perfect grounds" causing all SORTS of problems. If the PC-7 RF board isn't REALLY well-grounded to the chassis, your tuner may suddenly drift WILDLY off station, or noise can develop, or hum may appear. There are a MULTITUDE of problems that can slowly "creep in" to really cause you no END of headaches. Let's solve the "grounding issue" by making SURE the PC-7 RF board is REALLY grounded to the chassis. We do this by actually soldering the ground plane of the circuit board to the metal chassis in several places. Here's a picture of the result:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SmDQ7-FX4SI/AAAAAAAABG0/f7Puub3t1Wk/s400/PC-7%20soldered%20to%20chassis.JPG)
While it DOES take a LOT of heat to make a good solder joint between the chassis and the circuit board, we also need to be VERY careful so we don't destroy the circuit boards. Using your soldering GUN, heat the chassis right next to the location where you will be soldering the circuit board to the chassis. Once solder melts when you touch it to the chassis (not the tip of the gun), move the gun a *teensy* bit so it touches the copper ground plane of the PC-7 board itself. Now, apply solder to the chassis and "bridge the junction" between the circuit board and the chassis. Be EXTREMELY careful to make SURE no solder shorts to any other traces. Your overall goal will be to solder the PC-7 RF board to the chassis in several places. Concentrate on the area around the tuning capacitor, the Antenna Input area and the Output of the board to the IF strip (around the hole labeled "A"). See why I told you to make SURE the tuning capacitor positioning is correct? There is NO way to change it once the PC-7 RF board is firmly soldered to the chassis. (Note that the area adjacent to the hole for the ground wire to the Antenna Terminal has yet to be completely soldered. Once the PC-7 RF board is properly soldered to the chassis, check your work to make SURE there are no shorts and to make SURE the solder joints are truly SOLID!
Now, we're going to use the same technique to solder the PC-8MX IF board to the chassis. Things are a bit "tighter" on the IF board, but fortunately, there are no positioning "issues" to worry about. Let's take a look at some pictures of the soldered IF board. Here's the left side:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SmDSA9WGQfI/AAAAAAAABHE/jp3LsKRMIHk/s640/PC-8%20soldered%20to%20chassis%20-%20left.JPG)
Here's the left-center area of the board:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SmDQ70BgUWI/AAAAAAAABG4/gEEFSxnaoOo/s720/PC-8%20soldered%20to%20chassis%20-%20center.JPG)
Here's the right-center area of the board:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SmDQ8NQrJbI/AAAAAAAABG8/oT_tk7X_w_A/s720/PC-8%20soldered%20to%20chassis%20-%20center-right.JPG)
And finally, the right side of the IF board:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SmDSBuUVD-I/AAAAAAAABHI/9x46O_uDQvM/s720/PC-8%20soldered%20to%20chassis%20-%20right.JPG)
The area around the hole labeled #37 will be soldered to the chassis later. This hole will provide the "audio ground" for the PC-12 Multiplex board, so it really MUST be a GOOD solder joint. If not, you'll be chasing all *sorts* of "hum issues" later.
Here's a picture of the overall result after soldering the circuit boards to the chassis:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SmDQ7mwdbDI/AAAAAAAABGw/BTcj7SfqeGo/s576/Chassis%20Wiring%20-%20Chassis-Soldered%20Circuit%20Boards.JPG)
There is one additional item we are adding that is not covered in the manual. Since we are using a capacitor board to replace the quad capacitor, we need a place to make connect our B+ feeds so we've added an extra terminal strip. It is on the left side of this picture:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SmDBPBgALZI/AAAAAAAABGo/7zad17cVp2s/s640/Chassis%20Wiring%20-%20Added%20terminal%20strip.JPG)
NOW with all the preparations completed, we can finally "wire it all together." We'll cover *that* part of the build in our next update - coming VERY soon. Don't touch that dial *quite* yet! Soon. VERY Soon, we'll be ready to give that big, honkin' tuning capacitor a twirl. Until then, stay tuned!
Sincerely,
Bill Thomas
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July 21st, 2009 - Update: "Let's Put It All Together."
Remember the Stylistics? They made soft, sweet, soul music back in the 70's. Our "nearly new" FM-3 is *almost* ready to make some sweet music of its own, but first, we have to "put it all together." Let's get started!
Wit all of our preparations done, we can *basically* follow the usual instructions in the manual (with a few obvious exceptions). It all starts wit the tuning capacitor. We want to make SURE the tuning capacitor is REALLY grounded. The manual states that it isn't important to solder the ground connections to the chassis. I beg to differ. When Dynaco produced a "factory assembled" FM-3, THEY soldered the grounds to the chassis and YOU should too. Here's a picture to show you what I mean:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/SmDSB3VRtyI/AAAAAAAABHM/gbBZD-Pqask/s400/Tuning%20Capacitor%20Grounding.JPG)
You'll notice that the ground lugs are VERY securely soldered at the PC-7 RF board, but they are also soldered where the lugs protrude through the chassis. The better the ground, the more reliable your tuner will be. Use a similar technique to the one we used to solder the printed circuit boards to the chassis. Heat the chassis first and then allow the tip of the soldering GUN to contact the ground lugs of the tuning capacitor itself. Solder should easily join the two surfaces and also securely bond the ground wire to the lugs. It ain't "rocket science." Just make certain the solder joints are clean, shiny and secure. Once the tuning capacitor is soldered to the chassis and the PC-7 RF board, we move on to the Power Supply.
Since we are using a capacitor "board" to replace the (almost) unavailable quad capacitor, there are a few minor "revisions" to the construction of the tuner. The GOOD news is, our Power Supply is really "self-contained" on the capacitor board itself! All we *really* have to do is accommodate the wiring of the capacitor board. No problem! Here's a picture of the revised wiring:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SmDQ7sgQK9I/AAAAAAAABGs/7lezAJfdabo/s512/Chassis%20Wiring%20-%20Power%20Supply%20wiring%20changes.JPG)
There are only four wires that connect the capacito board to the tuner. I have color-coded them as follows: The Black wire is the Ground wire. Since we no longer have a chassis ground at the mounting lug for the quad capacitor, we connect the black wire to terminal #3 of the 5-lug terminal strip. This becomes the "central ground point" for the tuner. Notice that the center-tap of the High Voltage Secondary of the Power Transformer has also been moved to this point as well. The Red wire is the "input" connection to the capacitor board. It connects directly to pin 3 of the 6V4/EZ80 rectifier tube socket. The Orange wire is the same as the connection point for the third stage of the quad cap and the yellow wire is the same as the connection for the fourth and final stage of the quad cap. These two wires are terminated at our added terminal strip. The various B+ connections will route to these two terminals, making it EASY to convert back to a quad capacitor if someone wishes to do so later. And that's IT! Our Power Supply is ready to go!
The actual *wiring* of the FM-3 tuner is totally anti-climactic. There really aren't any "gotcha's" involved. It's simply a matter of making SURE you connect each wire between the two locations specified in the Construction Manual. You'll remember that I left a few components "unmounted" on the various circuit boards. I prefer to add these last components when the wiring is added around them. The first two parts to be added are the 10K Power Resistors on the PC-8MX IF board. Dynaco originally used 2 Watt resistors. BIG mistake! These resistors have to dissipate up to 2 Watts EACH! I prefer a MUCH greater "safety margin" by using 5 Watt resistors. They should be installed *off* the surface of the circuit board in order to allow for heat to be dissipated into the air, rather than the circuit board. Here's a picture at "eye level" to show you what I mean:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SmDS2s-gudI/AAAAAAAABHg/DwxX1DbKbCQ/s720/PC-8%20-%2090%20percent%20complete%20-%20Power%20Resistors%20-%20Front%20View.JPG)
And here's a picture from the top. The resistor on the right should be positioned away from the disc capacitor next to the IF transformer as shown:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SmDS2KAKaUI/AAAAAAAABHc/W8J-VFFsLW4/s576/PC-8%20-%2090%20percent%20complete%20-%20Power%20Resistors.JPG)
Some may question whether it is appropriate to use wire-wound resistors here due to the frequencies involved, but these resistors are decoupled by small capacitors so wire-wound resistors will work just fine!
We also have to mount the small PEC module replacement board on the IF circuit board. This picture shows why I wait until AFTER the circuit board is mounted to the chassis before adding the PEC module:
(http://lh3.ggpht.com/_Xp_4nF2BnZE/SmDS2mwg-7I/AAAAAAAABHk/PAU7vL14qzU/s576/PC-8%20-%2090%20percent%20complete%20-%20PEC%20installed.JPG)
It would be difficult to properly tighten the mounting screw for the PC-8MX IF board if the PEC module replacement were already installed, so it's best to install it *after* the circuit board is firmly screwed to the chassis. Notice that the discriminator transformer has not yet been mounted to the circuit board. This allows easy connection of the wiring from the EMM801 tuning eye socket on the front panel. But it also makes SURE the discriminator transformer isn't damaged due to the heat of soldering all the wires to the IF board. Other than that, ALL of the parts on the IF board are now mounted.
I'm sure you've noticed that there are a LOT of component leads that haven't been clipped yet. This picture shows what I'm talking about:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SmDS2ygIcdI/AAAAAAAABHo/zD2agWe0rCs/s400/PC-8%20-%2090%20percent%20complete.JPG)
There is *some* method to my madness. Wherever there is a circuit pad that will receive a wire, I leave the adjacent component leads long until the wire is soldered to the board. THEN I clip the component leads. If a component's solder connection happens to liquify while adding the wiring, it is a simple matter to re-solder the component. The long lead simply makes it easier to "snug" the component back down "flat" on the surface of the printed circuit board.
Here's a picture of the main chassis after about 75% of the wiring has been completed:
(http://lh6.ggpht.com/_Xp_4nF2BnZE/SmDUGgBbsaI/AAAAAAAABHw/mmbFGqRj-HM/s576/Chassis%20Wiring%20-%2075%20percent%20complete.JPG)
At this point, the PC-7 RF board has been completely wired, the PC-8MX IF board has also been completely wired and the PC-12 multiplex board is nearly wired as well, but there are still a *few* areas to deal with on the multiplex board. This picture should show you what I mean:
(http://lh4.ggpht.com/_Xp_4nF2BnZE/SmDSB-xkvmI/AAAAAAAABHQ/BA7n1LTxoCo/s512/PC-12%20-%2065%20percent%20complete%20-%20three-quarter%20view.JPG)
There is quite a bit of wiring that is done on top of the board, but the bottom side is *close* to complete. We'll cover the final chassis wiring along with the addition of the front panel wiring in our next update. It's *just* around the corner. Don't miss it!
Sincerely,
Bill Thomas
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Hi Bill,
Absolutely phenomenal work! Starting an FM-3 project with the "motherboard" soon.
You have probably stated this before, but I see that you are using solid wire. What gauge do you recommend--20 or 22 for general purpose chassis wiring??
Looks like PVC insulation.
Thanks and keep up the good work!
William
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Hi, William!
You are correct. I am using wire with PVC insulation. I tend to prefer 20 ga. wire for several reasons. The filament wires *do* carry enough current that it *might* make a difference. But the *main* reason I like 20 ga. has to do with those pesky eyelets. The larger wires "fill" the eyelet hole a little more. There is a larger "contact area" due to the larger circumference of the wire, as well as less solder between the surface of the wire and the inside of the eyelet hole.
In "plain-speak", it's just a little easier to work with the larger wire, but it's not really a "critical" concern.
I'll be posting another "update" shortly. This tuner looks like it's going to be purty swell! (Considering what it has taken to get to this point, it had BETTER be "purty swell" or *better!*) We'll find out together soon.
Sincerely,
Bill Thomas
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September 2nd, 2009 - Update: "At Long Last..."
The "Construction Phase" of our tuner rebuild is now complete! Let's take a look at *most* of the finished unit.
Let's start off with a shot of the front panel on our finished tuner.
(http://lh6.ggpht.com/_Xp_4nF2BnZE/Sp7SEWEqc9I/AAAAAAAABLk/aFRyDgU4u2s/s720/Completed%20Tuner%20-%20Front%20Shot.JPG)
Since we're using the same aluminum face plate we started with, this shot looks a LOT like the original "face plate shot" posted earlier. The parts have all been cleaned thoroughly so my grimy fingerprints are a thing of the past. I *did* wind up replacing the Volume Control knob to get rid of a "divot" in the original part.
Here's a picture of the completed tuner "from the top":
(http://lh5.ggpht.com/_Xp_4nF2BnZE/Sp7SEhZ8eXI/AAAAAAAABLo/ljgnkuVYOrk/s640/Completed%20Tuner%20-%20Top%20of%20Chassis%20Shot.JPG)
Looks a bit different than a "stock" FM-3, doesn't it? That "cleaner look" is mainly because these new circuit boards don't have the silk-screened legends on top of the boards. This is probably the only FM-3 with stock-style printed circuit boards that are now made from FR4 fiberglass.
Here's how things look from underneath the chassis:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/Sp7SE90b2hI/AAAAAAAABLs/L29c7ROgGmY/s720/Completed%20Tuner%20-%20Bottom%20of%20Chassis%20Shot.JPG)
Looks pretty much like a "standard" FM-3 tuner with the exception of the added terminal strip and the lack of a quad capacitor.
Let's look at the underside of the PC-12 multiplex board:
(http://lh5.ggpht.com/_Xp_4nF2BnZE/Sp7SFGvyxMI/AAAAAAAABL0/EvuOgL4zu9o/s720/Completed%20Tuner%20-%20Multiplex%20Board%20-%20Under%20Chassis%20Shot.JPG)
Other than the color of the printed circuit board substrate, this too looks quite "normal." Here's a picture of the multiplex board "from the top":
(http://lh6.ggpht.com/_Xp_4nF2BnZE/Sp7SEy8sylI/AAAAAAAABLw/OrysONSk_Ic/s576/Completed%20Tuner%20-%20Multiplex%20Board%20-%20Top%20Shot.JPG)
You'll notice a "mix" of metal-film and carbon-composition resistors. The metal-films are Dale/Vishay and Corning resistors. The carbon-comps are Allen-Bradleys. The metal films are used where carbon-comps might introduce a bit of added noise. The carbon-comps are used in the audio signal path for their "sonic signatures."
I would LOVE to tell you that things are all SWELL. Unfortunately, there appears to be a problem in the IF board. The tuner IS "making music", but attempts to properly align the IF strip have been less than satisfactory. In fact, this "problem" is the main reason it has taken so long to post pictures of the completed tuner.
In order to troubleshoot the IF board, I retrieved an FM alignment generator from storage. It too is a "Vintage Piece." Unfortunately, all these years of simply "sitting" in storage haven't been too kind to the generator either. I basically had to rebuild IT as well before I could use it to find our "alignment problem." Hoping to speed things up a bit, I "borrowed" a Vintage Heathkit FM generator from a local repair guy who was EXTREMELY kind in loaning it to me. Unfortunately, it ALSO has some "age issues." (SOME days, you just can't win!) So where does that leave us? Well, I am *almost* finished rebuilding *my* FM alignment generator and will be using it during the next week or so to FINALLY get to the bottom of the problem on the IF board.
That brings us up to date on the project. We have a completed tuner that plays music, but lacks the sensitivity a "normal" FM-3 should have. That too will be resolved VERY soon and I'll report on the eventual cause of the "difficulties." At least we know that the RF board and the Multiplex board are working properly. As soon as we can certify the performance of the IF board, we'll be ready to call this one "A Wrap!"
It's been a LONG time coming, but I feel quite certain this tuner will be "in the pink" within the next few days. Wish me luck!
Sincerely,
Bill Thomas
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So how is the IF board? Are we "in the pink" yet?
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Friday, January 29th, 2010 - Update: "It's Alive... It's Alive... It's ALIVE!!!"
There has been a LOT going on, personally speaking, so the final chapter on our "Second Dose of Fine Tuning" has been "on hold" - until NOW!
The truly AMAZING thing about Dynaco's FM-3 tuner is that you can properly align it without any expensive test equipment (unless you "tweak" the Primary of the first IF transformer like *I* did while trying to "troubleshoot" the IF problem earlier.) But if the Primary of the first IF transformer is set properly, everything else can be aligned using only the EMM801 tuning indicator. And this isn't a "compromise" situation either. You can get OUTSTANDING results - easily as good as using a whole cadre of test equipment. This also means you can easily KEEP the tuner in optimum alignment later, in case you have to change tubes or other parts. Pretty darned clever!
When we last left our FM-3 with the all new Printed Circuit Boards, we were having a problem with alignment. Between then and now, a bad capacitor was discovered *inside* one of the IF transformers. This rendered the tuner "un-alignable" for some time. The capacitor tested ok using my trusty, old Eico 950B R/C bridge UNTIL the Voltage on the part under test was raised above 200 Volts! Then it showed leakage. This one *teensy* little part had me "chasing my tail" for a LONG time, but the GOOD news is that the new IF circuit board was NOT the source of the problem! (It also meant that my initial fears of installing one of the IF transformers backwards was NOT the culprit.) But during the attempts at alignment, I managed to "tweak" the IF transformers WAY off the proper frequency of 10.7 MHz. It took a crystal-controlled signal source to get us back "into the ballpark" and properly functional again. Once the Primary of the first IF transformer was back "on-frequency", the rest of the IF alignment fell right into place.
IF alignment isn't rocket science. Simply follow the instructions in the FM-3 manual for aligning the IF section. As with most analog gear, it pays to go through the alignment several times in order to INSURE that you have "tweaked" every last bit of possible signal. You won't notice any LARGE changes the second or third time around, but you will probably find a *tiny* bit of improvement. After the third pass, leave it alone. Since these transformer adjustments are all "in-line," you don't really have a problem with adjustments interacting. It's simply a matter of peaking each transformer for maximum signal as shown on the lower portion of the EMM801. Remember to make these adjustments with the tuner set completely "between stations" so the only thing you hear is inter-station "hiss."
Once the IF transformers are properly "peaked" for maximum signal, it's time to move on to the discriminator adjustment. This is an absolutely CRITICAL adjustment and the tuner must be tuned "dead-center" into an FM station. This setting is best accomplished using the EMM801 tuning indicator. With a strong FM signal, the tuning indicator will close completely, but by "rocking" the tuning knob back and forth, you will be able to determine the EXACT center-point for the FM station. make SURE you don't allow this setting to change while making the discriminator adjustments. If it *does* move, you will have to start the discriminator alignment over.
The FM-3 manual describes two methods of aligning the discriminator. The "normal" method involves using the EMM801 as a "Voltmeter." This requires un-soldering and re-soldering several connections. The second method involves the use of a "VTVM" to set the discriminator alignment correctly. Well, things have changed since the days when the FM-3 was originally produced. Modern multimeters generally have a fairly high Input Impedance and will work just fine, but in order to keep the test equipment leads from de-tuning the discriminator due to lead capacitance, connect a 1 Meg resistor in series with the Positive lead of the multimeter. Use the other end of the resistor to connect to the tuner. Now you can back out the tuning slug on the top of the discriminator transformer and peak the bottom slug. Don't be too concerned if you can't get around 8 Volts at the prescribed measuring point - just adjust the lower slug for maximum Voltage. Then, adjust the top slug until the meter indicates as close to Zero as possible when the meter is connected to the other measuring point. That's it! Once this is done, don't forget to install the "gimmick capacitor" to eyelet #29 on the IF board.
Once the discriminator is correctly aligned, you *should* be able to hear local FM stations, but they will *probably* be in Mono. We'll get to the Stereo Multiplex board soon, but first, let's go "by the book" and align the RF board. This will make SURE the FM stations show up on the dial where they are supposed to be. It will also insure that the RF section of the tuner is operating at maximum sensitivity.
Unlike the IF adjustments, the RF adjustments tend to interact - a LOT! You will go back and forth MANY times while setting the oscillator adjustments for proper dial tracking. You will also spend a good bit of time going back and forth between the Antenna Coil and the Mixer Coil. The dial tracking adjustments of the oscillator are pretty sensitive. Small adjustments can make BIG changes in the dial tracking, but the Antenna Coil and Mixer Coil adjustments tend to be VERY broad and are not as "touchy."
Once the RF board has been aligned properly, there's only one section left: The Stereo Multiplex Decoder. Since we're measuring the signal strength of the 38 kHz sub-carrier, we need a Voltmeter capable of responding to MUCH higher frequencies than a typical multimeter can see. Fortunately, our trusty EMM801 can EASILY react to the 38 kHz sub-carrier level. Just follow the manual and make SURE the tuner is tuned EXACTLY to the center of a Stereo FM station's frequency. Temporarily connect the 1.2 Meg resistor to each Test Point and re-connect the EMM801 to the proper test points. When adjusting T71 and T72, you will find that the adjustments interact a bit so go back and forth several times until no further improvement can be made. Next, move the EMM801 connection to the second test point and adjust T73. These particular adjustments are absolutely CRITICAL for best Stereo separation and lowest distortion, so make them VERY carefully.
Guess what? You have just aligned a Dynaco FM-3 tuner! Once you've done it a few times, you'll find it pretty easy to do a full alignment in less than 30 minutes! Honest!
And THAT brings us (finally) to the completion of our "Second Dose of Fine Tuning." It's been *quite* a journey getting here. But the final result is a tuner that is sensitive, stable and sounds REALLY nice! Had I known that the original printed circuit boards were in such unreliable condition, I *might* have made some different decisions, but in a way, this has been a VERY positive outcome. Now, we have the "master artwork" available to produce NEW printed circuit boards that appear to be MUCH more reliable than the original phenolic boards and since those original phenolic boards are now approaching their 50 year anniversary, this is a VERY good thing!
The tuner is currently being "burned-in" for the next day or so to check for any instability or other "glitches," but it *appears* that everything is working just like a NEW tuner!
My SINCERE thanks to this tuner's owner. He has shown INCREDIBLE patience in waiting for his tuner to return from this VERY long odyssey! It will be shipped back home on Monday! I can hardly wait to hear what he thinks about his "new" tuner.
Now that the tuner has been completed, we can head on to our NEXT project! It will be a companion piece to one of our previous "projects" and it has been "waiting in the wings" for quite some time. THIS one will be really SUPER! I'll introduce you to it with a brand NEW thread, coming soon! Until then, keep those old Dynaco units working. If I can help answer your questions, just let me know. I don't have ALL the answers, but with each "project" our "collective knowledge base" increases markedly. Only GOOD can come from THAT!
Sincerely,
Bill Thomas
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Monday, February 1st, 2010 - Update: "One Last Thing..."
I thought it would be good to close our "Second Dose of Fine Tuning" report with the results of the "burn-in" process.
The completed and aligned tuner was "benched" and tested for the past few days. It proved to be totally stable within about two minutes of turn-on. (Dynaco suggests a 20 minute period to achieve full stability.) After numerous "heat-up/cool-down cycles," it appears to be an EXTREMELY stable unit. There is no sign of drift whatsoever. Both sections of the EMM801 tuning and stereo indicator close fully. This is not *always* the case with an FM-3 tuner, but THIS one appears to be operating at the "top of its class."
So how does it sound? Revealing! For those LOUSY FM stations that are compressed so badly they average over 90% modulation at all times, this tuner reveals just how DREADFUL this practice can be! But there is a local station that uses VERY little compression and in THIS case, the sound quality is simply magnificent! My brother decided to take a listen on headphones. He noticed a bit of a "rumbling" sound. I took a listen and realized it was rumble from the station's turntable! Another source eliminated that problem with the next selection. It was a well-recorded choir that was *probably* recorded using an M-S recording technique because every voice was positioned in a unique location in the Stereo sound field!
And WHAT a sound field! Separation is OUTSTANDING. Frequency response seems extended too; serving up the BEST that FM broadcasting has to offer. One of the GREATEST assets of the FM-3 tuner has to do with its ability to achieve full quieting with a poorer signal than other tuners. But THIS unit seems even better than most other FM-3's I have dealt with. Also, there is absolutely NO tendency for this tuner to be microphonic. Even relatively hard "taps" to every area of the chassis seem to be ignored.
So, we'll call this one DONE! The tuner is now on its way back to the original owner. I will relay any further information I receive, when it becomes available.
Sincerely,
Bill Thomas
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Great work, Bill. Nice that you have re-created the PCBs as well. This is something that I have been working on with one of my own FM-3s. The IF strip is a bit more challenging to recreate because if it's length, but it should be done shortly.
I have a question about the gimmick "capacitor".
The alignment instructions tell us to install this gimmick partway through the alignment process but doesn't explain why and doesn't tell us to remove it.
I've heard various responses on whether it is supposed to stay in or be removed after alignment.
What's you take on the situation?
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Actually, Dynaco *does* explain the reason for the "gimmick" capacitor. (sort of). According to Dynaco, "It corrects for the effects of interaction between the adjustments of the two slugs in the discriminator transformer." It is added after the discriminator transformer alignment has been completed. When re-aligning the discriminator transformer, the "gimmick" should be removed. After alignment, it should be replaced. It has no effect on the IF alignment or the RF alignment, but it really MUST be added after properly aligning the discriminator transformer in order to achieve the lowest distortion.
I hope that clears things up.
Sincerely,
Bill
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Bill,
The "gimmick" capacitor is a piece of wire extending 11/16" above PC-8. Is the value of this gimmick cap determined by both the length of the wire as well as the insulation? If so, would a gimmick based on a wire with Teflon insulation be any different than one with PVC insulation as when the tuner was designed? Basically, does the type of insulation matter?
Ron
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I would think technically yes. Most won't dispute that mylar is different from polypropylene which is different from paper/oil and different from polystyrene.
But the value of its capacitance must be infinitesimally small since it's basically sticking out in space and whatever capacitance it does generate would be to ground. A few femtofarads?
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I think that most of the confusion is based on Dynaco's own statement for the use of the gimmick cap. Obviously, the adjustment of the discriminator transformer occurs first. After that process is complete, you install the gimmick cap. Yet, Dynaco states the rationale for the gimmick as,
"... a small value capacitor which corrects for the effects of interaction between the adjustments of the two slugs in the discriminator transformer. At such times as realignment is performed, this "gimmick' should be removed before aligning the discriminator."
These two sentences seem to contradict each other as it would seem to imply that the "gimmick" needs to be present during the adjustment of T5. This of course is not the case, as the "gimmick" is installed after the adjustment process. Maybe Dynaco should have stated that it corrects for interaction of the slugs after adjustment is complete. That seems more accurate.
Ron
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I am thinking of buying a FM-3.
What should I look for. I assume the tuning eye is critical.
These were Kits so I assume quality varies.
Also is there a list of mods with instructions.
I guess the two power resistors and the "Berning Mod" PEC module. Is there a schematic for those modules.
Thanks George
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The PEC module mod is here as well as the power supply capacitor mod:http://quadesl.com/refurb/refurb_dynaFM3.html (http://quadesl.com/refurb/refurb_dynaFM3.html)
The other changes are summed up here including the power resistor mod:http://www.avahifi.com/root/audio_basics/1990-11_fm3_keep_working.htm (http://www.avahifi.com/root/audio_basics/1990-11_fm3_keep_working.htm)
If you are more concerned with functionality rather than aesthetics then you can use a single element EM84 tube instead of the dual element EMM801 but you would lose the stereocator indication. The stereo multiplexer would still work fine, though.
Instructions for that surgery are here:http://www.the-planet.org/dynaco/Tuner/Replacing%20EMM801%20with%20EM84.pdf (http://www.the-planet.org/dynaco/Tuner/Replacing%20EMM801%20with%20EM84.pdf)
PM me for other pitfalls.
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excellent article. one question: the PEC modules have to be adjusted to suit country's where the deemphasis constant is 50uS. doe sthsi also apply to the PEC module on the IF strip or just the PECs on the multiplexer board?
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Just the two PEC modules on the Multiplex board.
Bill
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thank you!
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If you do the "Berning Mod" to replace the original PEC modules (Which can be seen at Sheldon Stokes' website: http://www.quadesl.com/pdf/fm3_pec.pdf (http://www.quadesl.com/pdf/fm3_pec.pdf)), Change the value of the 510 pF capacitors to 340 pF. Since this is a non-standard value, you can either use 330 pF, or a parallel combination that equals 340 pF. Either method will be fine (You'll *probably* never hear the difference between a 340 and a 330 pF capacitor in this application.) This will be the correct value for the 50 microsecond de-emphasis necessary in Europe. Use either mica or polystyrene capacitors here. Works GREAT!
Hope this helps.
Bill
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Hi Bill,
Its great to see you back at AC again. Hope you are feeling much better these days.
For your information, we recently posted a small upgrade to our Ultimate 70, Ultravalve, and even stock Dyna St-70 amplifiers. All that is necessary is to install two 1N4007 diodes, one in series with each high voltage power transformer lead to the 5AR4 rectifier tube. The diodes will mount on unused 5AR4 socket pins. The purpose is to prolong the life of the rectifier by reducing the impact of cold hard turn-on AC voltage to the tube.
We recommend this for any vacuum tube amp using a 5AR4 rectifier tube.
Regards,
Frank Van Alstine
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Thanks, Frank!
I feel like such a stranger nowadays. I've been "tuned in" on the forum, but haven't felt much like any real meaningful *work* until this week.
Needless to say, I'm still a bit tired, but I *am* back and will be finishing up my "lingering projects" very shortly.
At least my "Life Force Meter" is getting LONGER these days. For awhile, I was a bit concerned that it was running out.
Getting old stinks, but there's only one thing worse - NOT getting old.
"Old" Bill
P.S. Thanks for the "mod" details. Makes GOOD sense to me! Especially with the quality of current production 5AR4/GZ34's.
Bill
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Hiya Bill,
thanks for the replies. I have also replaced the stereo PECs with the Berning mods adjusted to 50uS (340pF caps). I now find that there is too much treble (after two days of listening) and a fair amount of hiss. I also find i am getting very little variation when using the mono knob - that is very little stereo to mono change. I am using a strip antenna (not so great) so i wonder if a better antenna would help? Or do you think i should try align the Multiplexer board? I replaced the 47k resistors on the MPX board with 0.1% resistors but have had no change to stereo performance.
I was puzzling over the PEC boards and tried to simulate them in a SPICE program, unfortunately i really know nothing about RF or even complex electronics so could not simulate the input and output impedance's. nonetheless the graphs were quite interesting. i have attached a copy here. the Berning values give a dip at exactly 38kHz, our 50uS values do not dip at 38kHz (more 56kHz) and the dip is much shallower. I found that by adjusting the 100pF cap to 68pF the shape was corrected but i still suffer 8dBs less rejection of 38kHz.
Do you think this could be causing any of the problems i have outlined? Surely any extra bandwidth above 20kHz would not be audible? I would appreciate any input you can offer and any thoughts I am finding this a fascinating learning curve!
(http://www.audiocircle.com/image.php?id=34480)
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I think you're onto something, but first... "It's Philosophy Time!"
When attempting to evaluate a potential "improvement" in a unit's performance, you need to run a "baseline test" on the unit, but you NEED to make sure the unit is operating as well as it can be. (Of course, one could argue that a *true* "baseline test" would include running a test prior to alignment, but we have some "prior knowledge" about the FM-3's alignment.)
Throughout the entire Monaural section of the tuner, adjustments are fairly broad. (It is important to be as accurate as possible with the Discriminator alignment, but otherwise, things are pretty simple.)
When you get to the multiplex board, the adjustment to T-71 and T-72 is broad and well-pronounced. T-73 is a bit of a bear. EXTREMELY small movement of the slugs can make a BIG difference in the Stereo Separation and noise rejection.
So, before you go any further, I would STRONGLY recommend doing an alignment of the Multiplex board. I think you will find the separation will improve - even with the strip antenna.
As for your research, I think you are DEFINITELY on the right track. The earlier FM-3 that I modified for 50 microsecond response didn't seem to suffer from the same issues. Sure, it was "bright" when listening to US stations' 75 microsecond pre-emphasis, but it was no more pronounced than listening to a dolby B encoded tape with the dolby decoder off. (That's probably the closest I can "describe" a sound quality in print.)
By the way, I wouldn't bother aligning the rest of the tuner at this point, but if your Multiplex section is WAAYYY off, I'd consider doing at least a Discriminator alignment before aligning the Multiplex board.
Either way, it *does* appear that the 100 pF capacitor should *probably* be reduced to 68 pF for proper performance. Next time I do an FM-3, I'll try to do a comparison, but in theory, it looks like you're right on this.
I LOVE to learn!
Sincerely,
Bill Thomas
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thnaks for the reply bill.
I did try to realign the mulltiplex board but using a multimeter as described in the application note on replacing the eye tube with an EM84. There the instruction ask one to adjust T72 & T71 until one gets a as high a voltage on TP75 as possible. I started at 14V and ended off with 30V....but it didn't make a huge difference. Some fiddling with T73 made a very small difference. I will return to that. I will also try replacing the 6BL8. By the way my stereo indicator closes fully.
I am beginning to suspect the pull out switch as well. Looking at the schematic surely if one engages the mono switch the PECs are completely bypassed? Then shouldnt their contribution (brightness) be minimised? I briefly measured the resistance of the switch (in circuit) and it appeared a bit high perhaps this is the issue?
I cant say that there was a huge change from the 100pF to the 68pF but i feel more comfortable with it. Still it would be great if someone could work out a PEC layout that matched the 50uS time constant AND suppressed 38kHz.
I have a problem aligning the discriminator; where i live there are no mono stations! Any suggestions as to how i can proceed?
Thanks for the great assistance!
regards
johnny
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The earlier FM-3 that I modified for 50 microsecond response didn't seem to suffer from the same issues. Sure, it was "bright" when listening to US stations' 75 microsecond pre-emphasis,
No sign of 'brightness' here in UK Bill, sound's great :thumb:
Jim
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Hi, I'm looking for files of Dinaco FM-3 circuit boards(Gerber files and drill file) for my project of restoring this receiver. Who can share the link?. Or buy ready-made :D
Thank you.
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The FM3 dates to decades before there was anything like Gerber files, so these probably don't exist.
If you are trying to maintain and/or restore an FM3, I strongly recommend checking out the following resources:
"Keeping the Dyna FM3 Working" (http://www.avahifi.com/images/avahifi/root/audio_basics/ab_pdf/ab1990-11.pdf) By Frank van Alstine (he has a forum here). A MUST-read for anyone trying to, well, keep the Dyna FM-3 working. Article starts at the bottom of Page 4. There is another version with suggestions from a reader for additional "fixes". Not in the linked file or on the website as far as I can tell but I can email you a copy if you PM me.
Link for upgrade parts (EQ modules, power supply etc) (http://quadesl.com/refurb/refurb_dynaFM3.html)
Another great source for parts (http://fm3zone.com/) ranging from substitute PEC de-emphasis modules and an LED pilot light that reduces the load on the power supply all the way up to a full CAD-designed replacement motherboard that replaces almost all point-to-point wiring.
I also have a copy of the Dynaco service bulletin detailing how to substitute the EM84 tuning-eye tube if anyone needs it.
If you really want everything you can get from the stock circuit, you might want to consider pulling the boards and replacing the ancient carbon-comp resistors with modern film types. They have probably all "cooked" out oof spec and there are several places where Dyna originally used tighter-tolerance parts (some in pairs) for performance reasons. If you don't mind spending a little time with a multimeter, you can match these parts much tighter than Dyna was willing to pay for. (Due to the cramped layout, many of these parts are hard to get to with the boards installed.)
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Thank you, this is very useful information!
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One other thing, when I had mine, a little research turned up 'mil-spec' versions of many of the tubes, mainly in the RF and IF sections and the MPX switching tube. I lacked test equipment to validate possible performance improvements, but they worked well and didn't cost much more than the 'street' tubes you find.
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The values of the mica caps inside the I.F. Transformer, Diskcriminator transformer and T71,T72,T73 Transformer is not given on the schematic. My multimeter will measure capacitance, but have had no luck getting accurate values of the existing mica caps so far.
Who knows the exact values of these capacitors?
Thanks!
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Since those caps are not replaceable/interchangeable, I'm not sure what help knowing those values would be, but if anyone would know, it would be this guy. (https://dynacodesigns.com/) He has offered parts and upgrades for the FM-3 (even a replacement motherboard that eliminates most of the wiring) for years.
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Yes, I saw this resource, thank you.
I want to say that the use of UHF blocks on one board is not desirable.
It is also not advisable to use two-sided mounting in devices with a power supply of more than 250 volts.
I made gerber files of PC-7, PC-8, PC-12 PCBs, leaving the correct installation but improving the screening between the conductors. After checking, I'll post these files here.
(http://www.audiocircle.com/image.php?id=165841)
(http://www.audiocircle.com/image.php?id=165842)
(http://www.audiocircle.com/image.php?id=165843)
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Interesting; you're saying there are design issues with the 'uniboard'?
Only curious because I used to own an FM-3.
By 'UHF blocks' are you referring to the chokes on the boards? There are some there that are counterproductive?
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I meant that RF Filter, RF Amplifer, Mixer is better separated from IF Filter and IF Amplifer, which was done in the original receiver design.
There are industry standards for designing printed circuit boards and mounting densities.
Dynaco printed circuit boards are made in category A.
Therefore I think that it is not right to have all the elements of the circuit on one board.
Here are my thoughts on how to improve this receiver.
1.New printed circuit boards with improved shielding of conductors, for better elimination of parasitic capacitances.
2. Replacing the built-in capacitors in the coils and replacing the paper frames with polystyrene ones, this will increase the quality of the coils and selectivity along the adjacent channel.
3. Complete replacement of passive elements by more accurate ones.
4.Change the old capacitor C8
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New design of PEC 555001
(http://www.audiocircle.com/image.php?id=165888)
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(http://www.audiocircle.com/image.php?id=171632)
Hi. My project is moving, today I received a PCB.
As promised I post Gerber files.
Maybe someone from the community will come in handy.
DYNACO FM-3 PC-7 https://www.dropbox.com/sh/gsyg7av81wvm23o/AADBv_BRhmTJboJ37Zdh1KfTa?dl=0
DYNACO FM-3 PC-8 https://www.dropbox.com/sh/u2itpy3n9uwq1a6/AABSdYUF6hwC93mCNf1P5_B6a?dl=0
DYNACO FM-3 PC-12 https://www.dropbox.com/sh/p324rtdt1mspgkn/AAB4wuIYqH2UZw_S5h_-UI30a?dl=0
DYNACO FM-3 PEC 555001 https://www.dropbox.com/sh/wghz1qwtspxdra5/AADpZ-r2lbEalXj71nge4DINa?dl=0
DYNACO FM-3 PEC 555004 https://www.dropbox.com/sh/chamv2lnm108r7q/AACtqSOfsPXz08WF76UlLiZTa?dl=0
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Do your revised PEC modules incorporate the de-emphasis changes I've seen in some other offerings?
Thanks for resurrecting this. Bill Thomas is long gone but there are still some of these around. Back in my day (Pepperidge Farm remembers?), an FM tuner was considered an essential part of an audio system. Now, few seem to use one, there's never any threads on forums about them, and I have never seen one at any of the numerous audio shows I've been to.
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(http://www.audiocircle.com/image.php?id=171646)
PEC 555004 standard
PEC 555001 is upgraded as in the article James Lin.
All PCB in Gerber files reproduce the original as much as possible.
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I found one page on modifying the RF board; is there a complete-article link? Still interested in this classic tuner even though I gave mine away on freecycle a few years ago.
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In the RF Circuit Board, I changed only the C-8 capacitor to a modern GAA 10006 and metalized the holes in the fastening screws to lower the impedance.
Here are all the documents that I have, the rest of the book on the calculation and design of printed circuit boards, but they are in Russian)))
https://www.dropbox.com/s/f5fregrbxhte9c0/d86717_0187c74ac9204e52efd2930399114af3-464168.pdf?dl=0
https://www.dropbox.com/s/svioaiw73tqdce9/EMM801-EM84.pdf?dl=0
https://www.dropbox.com/s/m3ivq3o91zmbog3/FMX%203.pdf?dl=0
https://www.dropbox.com/s/omllwx7dnesz242/Improving%20Dynaco%20FM-3.pdf?dl=0
https://www.dropbox.com/s/6mdspy5oj4vl6ml/Keeping%20the%20Dyna%20FM-3%20Working.pdf?dl=0
https://www.dropbox.com/s/utgjg7igwagh6r8/LED_from_6.3VAC.png%20400%C3%97360%20pixels.pdf?dl=0
https://www.dropbox.com/s/hw7mcnabjzl40ux/MULTICOR_PRIPOY.pdf?dl=0
https://www.dropbox.com/s/fc32fd081buopuk/Untitled%208.pdf?dl=0
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How is the work going? Did you manage to restore the tuner?
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Hi. Now I am working on new inductors made of modern materials. The goal is to increase the quality of the circuits.
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Hi guzeev,
Do you have PCB set for sale ?
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Will be a month later on ebay. My ebay User ID guzeevs
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Having acquired an FM-3, plus a spare EMM801 magic-eye tube, I'm interested in a set of boards.
Rebuilding any formaldehyde-phenolic board is difficult, even with a temperature controlled desoldering station.
Do let us know when these are available.
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Hi, I ordered a batch of 10 pieces, waiting for delivery.
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Hi guzeev,
Any news about PCB set ?
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Could anyone perhaps share the electrical characteristic of the sections of the PA-509 transformer used in the FM-3?
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Yes, I saw this resource, thank you.
I want to say that the use of UHF blocks on one board is not desirable.
It is also not advisable to use two-sided mounting in devices with a power supply of more than 250 volts.
I made gerber files of PC-7, PC-8, PC-12 PCBs, leaving the correct installation but improving the screening between the conductors. After checking, I'll post these files here.
(http://www.audiocircle.com/image.php?id=165841)
(http://www.audiocircle.com/image.php?id=165842)
(http://www.audiocircle.com/image.php?id=165843)
Hi,
Can you please upload the gerber file of PC-7 using GAA10006 trimmer.
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Hi guzeev,
I want to make the PCB set of FM3 but there is an error in top layer of PC12 design top layer PAD incomplete (in Yellow color) and no solder musk on pin of T71,T72,T73 can you please check this ?
(https://www.audiocircle.com/image.php?id=195266)
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Hi, I ordered a batch of 10 pieces, waiting for delivery.
I checked eBay but never saw these listed for sale.
Are these available?
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I checked eBay but never saw these listed for sale.
Are these available?
3 set of PCB available for sale
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New PCB arrived....
(https://i.ibb.co/L569mRW/20190705-115859.jpg) (https://ibb.co/rsM5Y0S)
(https://i.ibb.co/5sgy9Qy/20190705-115930.jpg) (https://ibb.co/8PLpByp)
(https://i.ibb.co/g9Vq0D9/20190705-120326.jpg) (https://ibb.co/yPSvz8P)
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Repost from:
Re: Dynaco FM-3 rebuild - "A Double Dose of Fine Tuning!" https://www.audiocircle.com/index.php?topic=62800.msg1836509#msg1836509 (https://www.audiocircle.com/index.php?topic=62800.msg1836509#msg1836509)
A member over at the The Dynaco Tube Audio Forum named 'Stewdan' set me up with the web files for the threads up to reply 44 of the original 'Double Dose of Fine Tuning!' thread & up to reply 32 on 'Our "Second Dose" of "Fine Tuning" - A TOTAL Dynaco FM-3 reconstruction.
I put them in PDF format on a Google Drive. Here are the links:
Dynaco FM-3 rebuild - _A Double Dose of Fine Tuning!_Full Thread through Post 44
https://drive.google.com/file/d/15B4E107St_x4lreS8CbOvAXRWc03PuEd/view?usp=sharing (https://drive.google.com/file/d/15B4E107St_x4lreS8CbOvAXRWc03PuEd/view?usp=sharing)
Our _Second Dose_ of _Fine Tuning_ - A TOTAL Dynaco FM-3 reconstruction!
https://drive.google.com/file/d/1j6kd8F3-mOOYvZcI69YVaoRzha4uJ-id/view?usp=sharing (https://drive.google.com/file/d/1j6kd8F3-mOOYvZcI69YVaoRzha4uJ-id/view?usp=sharing)
Hope this helps!
Cheers,
Aguaazul
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Coming to the party very late, but here goes.
I have a pair of working FM3s. I would like to rebuild one completely, starting with new PCBs.
I have several options for PCBs, the first being to buy some from someone. Sadly, I can't find anyone selling them.
Next option is to have some made. This of course requires some Gerber files. Now, I could lay out some boards myself, but that's a lot of work and lots of room for error.
I see that someone DID lay out some boards and even made the files available here. That's probably a better option than doing it myself. More sadness though: those links are now dead.
So, can anyone help me with a source for boards or links to those old gerbers or ...
Thanks in advance.
Alan
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Maybe you could google Dynaco FM3 or Dynaco FM 3 price.
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Maybe you could google Dynaco FM3 or Dynaco FM 3 price.
Ahh, why? Neither would get me a link to FM3 PCBs, which is what I'm looking for.
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Ahh, why? Neither would get me a link to FM3 PCBs, which is what I'm looking for.
Feel free tô google FM3 PCB or anything else. :thumb:
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Try here:
https://dynacodesigns.wordpress.com/fm-3-kits-and-parts/
I used the single board and other parts from them. The single board looks out of stock. May want to contact them for an ETA.
Ron
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Repost from:
Re: Dynaco FM-3 rebuild - "A Double Dose of Fine Tuning!" https://www.audiocircle.com/index.php?topic=62800.msg1836509#msg1836509 (https://www.audiocircle.com/index.php?topic=62800.msg1836509#msg1836509)
A member over at the The Dynaco Tube Audio Forum named 'Stewdan' set me up with the web files for the threads up to reply 44 of the original 'Double Dose of Fine Tuning!' thread & up to reply 32 on 'Our "Second Dose" of "Fine Tuning" - A TOTAL Dynaco FM-3 reconstruction.
I put them in PDF format on a Google Drive. Here are the links:
Dynaco FM-3 rebuild - _A Double Dose of Fine Tuning!_Full Thread through Post 44
https://drive.google.com/file/d/15B4E107St_x4lreS8CbOvAXRWc03PuEd/view?usp=sharing (https://drive.google.com/file/d/15B4E107St_x4lreS8CbOvAXRWc03PuEd/view?usp=sharing)
Our _Second Dose_ of _Fine Tuning_ - A TOTAL Dynaco FM-3 reconstruction!
https://drive.google.com/file/d/1j6kd8F3-mOOYvZcI69YVaoRzha4uJ-id/view?usp=sharing (https://drive.google.com/file/d/1j6kd8F3-mOOYvZcI69YVaoRzha4uJ-id/view?usp=sharing)
Hope this helps!
Cheers,
Aguaazul
Thanks for this....just bought an FM3....and the pics will be very helpful
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Coming to the party very late, but here goes.
I have a pair of working FM3s. I would like to rebuild one completely, starting with new PCBs.
I have several options for PCBs, the first being to buy some from someone. Sadly, I can't find anyone selling them.
Next option is to have some made. This of course requires some Gerber files. Now, I could lay out some boards myself, but that's a lot of work and lots of room for error.
I see that someone DID lay out some boards and even made the files available here. That's probably a better option than doing it myself. More sadness though: those links are now dead.
So, can anyone help me with a source for boards or links to those old gerbers or ...
Thanks in advance.
Alan
I have 3 set of PCB and also have the Gerber file if you need please let me know.
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I am interested in purchasing the FM3 pc boards or the gerber files that arindamcc has. I’m a new member who doesn’t have my 3x posts so I can’t direct message. : )
I’m rebuilding an FM3 to go along with the Fisher X-202-B I listen to every day. My FM3 works, but the PC-8MX is warped and I don’t think it will survive the rebuild. I’m looking forward to finally having a good valve-tuner.
Thank you!
- greg
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I finally managed to buy an FM-3, I want to completely restore it, but here in Hungary it is not easy to get parts for it. My other problem is that the PCBs are damaged (cracked and burned) in several places and need to be replaced. I could create it myself if someone could share the PCB plans or gerber file with me.
I am interested in purchasing the FM3 pc boards or the gerber files that arindamcc has. I'm a new member who doesn't have my 3x posts so I can't direct message. :)
Thanks in advance for your help...
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A big shout out to arindamcc for passing on the FM3 Gerber files.
Thank you!!
- g
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Hi,
Many thanks to BuddyDave for his offer to send the gerbers. I redrew the PCBs for myself and rebuilt them. Unfortunately, the original stereo decoder could not be revived. I built a commonly used solution instead. It works great.
There is a 200V stabilizer on the panel, the tuner and the output adjustment work from this, there is an auxiliary power supply for the TA7343AP, and the ST decoder ( TA7343AP )
( Sorry for my bad English, but unfortunately I can only communicate with a translator.)
Attila
(https://www.audiocircle.com/image.php?id=252374)
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Hi All
Can someone please send me a copy of the Gerber files for the 3 FM3 boards
Sincerely
Michael Heit
mheit61@gmail.com
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I'm looking for information about coils (number of turns, wire, dimensions)
I am very interested in information about IF transformers (photos, what kind of wire they are wound with, the number of turns, the dimensions of the frames).
Can someone please send me a copy of the Gerber files for the 3 FM3 boards
Help who has information....
pkuz82@gmail.com
Sincerely
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Tell me the size of the printed circuit board, I determined it to be 120mm * 80mm, is it the right size?
(https://www.audiocircle.com/image.php?id=259573)