[Bill Thomas]

December 18th, 2008 - Update:  "A Little Bit of History!"

     Dynaco's FM-3 tuner is a thoroughly REMARKABLE piece of electronic engineering.  Not because it provides the highest sensitivity of any tube-based FM tuner (It doesn't!)  Not because it has greater ability to separate closely spaced signals on the FM band.  (It doesn't do that either!)  So why on earth would ANYONE be interested in such a tuner?  Because it is one of the most truly *musical* tuners on the planet!  So, is *that* what makes it so remarkable?  Nope!

     What makes the Dynaco FM-3 tuner so thoroughly remarkable is that ANYONE who is able to solder can build one from scratch, and then completely ALIGN it with absolutely NO test equipment of any kind!  Now *that* is TRULY remarkable.  Of course, it doesn't hurt that a properly constructed and aligned tuner simply sounds SO good!

     The FM-3 tuner was actually an update of Dynaco's FM-1 tuner.  The FM-1 was introduced in 1961 as a monophonic tuner.  It was based on a design by Stewart Hegeman, and Ed Laurent (the "father" of so many of Dynaco's "classic" tube components) made the design a reality.  It featured a brass face plate and brown plastic knobs, very similar in styling to the PAS-2 preamplifier.  In kit form, the FM-1 sold for just $79.95!  (That's $560.05 in today's Dollars.)  If you weren't very good at soldering, you could purchase a factory-wired version for $99.95  ($700.15 in today's Dollars.)

     The FM-1, while a Monaural tuner, was designed with Stereo in mind.  Space was reserved on the chassis to add one of two "accessory modules."  One of those modules was a 17 Watt amplifier module that turned the FM-1 into a complete table-model radio - all you had to add was a speaker.  But the other module was a multiplex adapter that turned the Monaural FM-1 tuner into a complete Stereophonic tuner.  It was pretty easy to tell which module Dynaco had in mind.  The metal plate that covered the hole in the chassis had "reserved for multiplex adapter" printed on it!

     The multiplex adapter was designed by Sid Lidz and provided greater than 30 dB of separation.  This may not sound like a lot, but back "in the day" it was common for tuners to really *struggle* to provide more than 25 dB of separation.  To put things into perspective, it is very UN-common for a phono cartridge to provide more than 35 dB of separation, even today!  Here's a picture of the front of an FM-1 tuner that has been converted to Stereo operation with the addition of the multiplex adapter:

                   

     The FM-3 tuner was introduced in 1964 and basically took all the elements of the FM-1 (with the Stereo adapter included) and put them into a restyled unit featuring Dynaco's "Champagne Gold" face plate.  It also added a new twist:  By pulling on the Volume Control knob, you could activate a switch that forced the Stereo tuner into Monaural operation - VERY handy during low-signal conditions.

     This is a *bit* of a "simplification."  There were actually two versions of the FM-3 tuner, but for all practical purposes, they were quite similar.  Dynaco even sold "upgrade kits" that allowed FM-1 owners to replace the face plate and knobs with the more modern "Champagne Gold" versions.  Here's a picture of an early version of the FM-3 tuner:

                   

     Today, FM-3 tuners are commonly sold on eBay at rock-bottom prices.  The problem is, many of these units (if they work at all) suffer from "rock bottom performance" as well.  They hum, they drift and have little or no stereo separation.  Why?  As with most tube-type electronics, HEAT is thy enemy!  After many years of faithful service, an FM-3 tuner will suffer from poor alignment, resistors that have drifted in value, bad tubes and one more "little" problem:  The FM-3 tuner uses a dual "magic-eye" indicator tube that was discontinued by 1970!  In fact, Dynaco sent out a letter to it's dealers and even some of the purchasers of its tuners offering to buy "any and all" EMM801's that might be available - even a quantity of ONE!  Sadly, they were unable to procure enough of them to continue production and the FM-3 was quietly discontinued around 1970.  So why even bother trying to restore one today?  Because when properly operating, they simply sound SO good!

     Restoring an FM-3 tuner today is complicated by the fact that MANY of its parts are now made of "unobtainium."  If you happen to own an FM-3 tuner, or are considering buying one, do yourself a favor and also buy a "parts unit" in order to have replacement parts available to properly restore and repair your existing tuner.

     If you are thinking of buying an eBay unit, here are some things to watch out for:  Does the tuning capacitor operate smoothly with no "play" in the tuning knob?  Do the plates of the tuning capacitor mesh without touching?  Does it have all of its original tubes?  (This is ONE time you certainly hope it does!  Dynaco used two Telefunken 12AX7's in the FM-3 - needless to say, they are VERY desirable, but chances are, they were "harvested" by the eBay seller and sold for BIG bucks elsewhere!)  Are all tube shields present?  (Every tube except the rectifier and the tuning indicator should have a shield).  Is the tuning indicator tube present and does it light up with a normal blue-green glow?  Replacements ARE available, but they are expensive!  (I may possibly have the largest stock of NOS Telefunken EMM801's in the WORLD - about thirty!)  Does the unit pick up ANY signals and play them?  If it DOES make SOME sound, when you tune it, is there a "scratchiness" to the audio when tuning?  Is there ANY stereo separation at all?  What about cosmetics?  Does your potential "candidate" have a nice looking face plate and knobs, with all lettering intact?  And here's one more tip:  Do the IF transformers have a flat top, or a "sloped top?"  (You want the ones with the "sloped top.")  If the answers to the above questions are in the affirmative, there is "probably" no reason why you can't restore your FM-3 tuner back into the "picture of health!"

     In response to our "poll question" we are going to be restoring an FM-3 tuner - just to see exactly how difficult it will be.  But not only that, we're going to be rebuilding TWO of them at the same time.  One will feature Allen-Bradley carbon composition resistors (much like an original FM-3), while the other one will feature more modern metal-film resistors.  There are reports that metal film resistors have a tendency to compromise the performance of an FM-3 tuner, and I wanted to see for myself if this is actually the case.  When we're finished, we'll have at least ONE (mostly) new Dynaco FM-3 tuner!  With REAL luck, we'll have TWO of them!  Cross your fingers and hold on tight, this is gonna be REALLY fun!

Sincerely,

Bill Thomas

[Bill Thomas]

December 19th, 2008 - Update:  "Let's Look Under the Hood!"

     Just a brief update to give you an idea of what you may expect to find once you pop the cover off an FM-3.  The FM-3 pictured in our first update isn't going to be the "foundation" of either of our finished builds.  It's one of our "parts units."  First, take a look at the overall look of a typical FM-3 in "as found" condition - complete with dust and dirt!

                   

     The first thing you'll probably notice is a couple of missing tubes.  Yep!  The Telefunken 12AX7's (and their shields) were "harvested" by the previous owner.  Since even used Telefunken 12AX7's are going for more than a hundred bucks a pop, it's to be expected.  Since I purchased this particular unit as a "parts unit" several years ago, I won't hold it against the seller.  The price was right - this particular unit cost around $30.00!  But there are other problem areas to look out for.  Besides the dirt and discoloration of the metalwork, the MAIN reason I won't be using this as the "foundation" for a rebuild is shown here:

                   

     Notice the IF transformers?  They are the "flat top" versions.  These were used in the FM-1 and early versions of the FM-3 tuner.  The problem with these particular transformers is that they have a tendency to "open up" due to the high heat inside the tuner.  They also have a tendency for the tuning slugs to "jam" rendering them "non-adjustable."  The IF transformers we *want* look like the discriminator transformer at the far left side of the photo.

     Here's another "problem area":

                   

     You have to wonder how the inside front panel got bent this way.  Simply bizarre!

     On the positive side, the tuning capacitor has NO play to speak of.  It operates smoothly and it *appears* that it will be suitable for transplanting (if necessary).  We can't give it a TOTALLY clean bill of health yet, but initial appearances are encouraging.  We'll know more once we remove the capacitor's shield.

     Also on the positive side, our previous owner left the EMM801 tuning indicator tube in place.  To be honest, it really doesn't matter because our completed tuner will have a NOS EMM801 installed, but at least this thing wasn't COMPLETELY stripped.

     So, we won't be using this tuner for anything more than parts.  But, it's good to know that it's fairly complete.  There are other parts that are impossible to find today and this tuner has them all.  (We'll cover those "other" parts as we progress with the build.

     By the way, since the FM-1 pictured also contains the same "flat top" IF transformers, we won't be using it as the "foundation" for one of our builds either.  Its tuning capacitor has a bit of "wobble" to it as well.  We'll look further and see if there's a better unit to use for our build.  I'll report my findings in our next update.  Watch for it!

Sincerely,

Bill Thomas

[avahifi]

Just wondering when you are going to finish the Ultimate 70 rebuild you started in November?

Regards,

Frank Van Alstine

[WGH]

Wow, I built an FM-3 when I was in high school in '65 or '66. Great sound but as you mentioned it had terrible station drift as it warmed up. I wonder what happened to it? Maybe it is one of your parts units.

I also built a Dynaco SCA-80, also missing - those 10 years after high school are pretty foggy (for many reasons).

I'll be following the re-build, looks like fun.

Wayne

[Bill Thomas]

Hi, Frank!

     We've had a long string of rainy or cold days, so I am stalled on the final painting of the Transformers.  I have made arrangements to do the painting at another location, but that has to wait until the "keeper of the shop" returns from his Christmas break!  I'll be wrapping things up on the "Ultimate Stereo 70" before the year is out - PROMISE!  (I'm REALLY "itchin'" to get it finished myself!)

Hi, Wayne!

     Sorry to hear yours drifted.  There are LOTS of potential causes, but the most common reasons are a few "critical parts" on the RF board.  That little "ceramic trimmer" is one of the most likely culprits.  We're going to try to work around that problem on our builds.  No promises, but we'll see if my "solution" has any merit.

Sincerely,

Bill Thomas

[Bill Thomas]

December 19th, 2008 - Update #2:  "Presenting: Our Candidates!"

     In our last update, we showed you what turned out to be our "parts unit."  Now, let's look at the "real deal" - I'm calling this one "Candidate Number One."  Here's a picture from the top of the chassis:

                   

     This unit has the desired IF transformers.  Notice the sloped tops on ALL of the IF transformers.  These are quite a bit more reliable than the "flat top" versions.  The REST of the chassis is nothing to write home about.  This unit was *obviously* stored in a "less than desirable location.  The metalwork shows signs of SERIOUS oxidation.  It would be a royal PAIN to get this cleaned up.  On top of that, it has other problems.  The tuning capacitor has too much play, so the end result would be a tuner that "jumped stations" when you tapped on it, or when it warmed up.  Fortunately, we have a GOOD one available on our FM-3 "parts unit."

     Taking a look "under the hood" we see the probable reason this unit was retired.  Here's a picture:

         

     It's pretty obvious the quad capacitor is "toast!"  That crusty leakage is a "classic" sign of a REALLY bad electrolytic capacitor.  No worries!  We'll be replacing it in our rebuild.

     Taking a look back on top of the unit, here's a picture of the Multiplex Board:

                   

     This board appears to be in pretty good condition.  The tube shields aren't great, but fortunately, we have some prettier ones available.

     Now, here's a picture of the RF board:

                   

     There's something funny going on here.  Most FM-3's of this vintage have a Printed Circuit board made of Epoxy/Fiberglas.  THIS one is a MUCH earlier phenolic version.  It looks like someone replaced the RF board with one from an earlier tuner.  I'm betting this was an attempt to solve a problem with drift.  MAYBE it helped, but I'm betting the REAL cause was the tuning capacitor.  Nice try!  Still, we'll need this board for the first IF transformer.

     Interestingly, this tuner was a factory-wired unit.  It's a pity it is in such poor overall condition.  It would have been nice to use this one for our "mostly stock" rebuild.  Oh well.

     So, out of three tuners (so far), we have enough reasonably decent parts to make ONE completed tuner.  NOW do you see why I SERIOUSLY recommend buying some "parts units" before beginning YOUR restoration?  The GOOD news is that many of the "wear items", like that special Volume Control/Stereo-Mono switch will be replaced with NOS originals from my Dynaco "parts stash."

     Now, let's take a look at "Candidate Number Two."  Here's a picture from topside:

                   

     Not exactly something that would instill a lot of confidence, is it?  But, there are LOTS of good parts here, as well as the desirable IF Transformers.  Unfortunately, the main Tuning Capacitor is NOT one of the usable parts.  Take a closer look:



     If you guessed that was a finishing nail holding the planetary drive together, you guessed right!  On top of that, this capacitor has lost some ball bearings.  It's is a GONER!  You'll also notice that the plastic tuning dial has a big ol' crack.  It's destined for the garbage can.

     Here's an overall picture of the RF board:

                             

     THIS one has the Epoxy/Fiberglas board.  It's a little "crusty", but it *should* clean up pretty well.  Let's *hope* so - we're gonna need it!

     Here's the Multiplex board in all its "radiant glory":

                   

     And finally, here's a picture of the underside of this chassis:

                   

     This was a kit version and whoever built it wasn't *quite* as neat as he should have been.  When dealing with frequencies in the MHz range, sloppy wiring (and a VERY loose main filter capacitor) don't help the cause a lot.  No biggie.  We'll take care of it all in our rebuild!

     Well, out of FOUR tuners, we have all the necessary parts needed to build - ONE tuner!  Yep!  It's gonna take one MORE "parts unit" to get another good Main Tuning Capacitor!  But that's enough for today's updates.  Now, it on to the "unbuilding process" and selecting the metal parts to clean up for two tuners.  More to come - Stay Tuned!

Sincerely,

Bill Thomas

[Bill Thomas]

December 19th, 2008 - Update Three:  - "Sad News!"

     It is my sad duty to inform everyone that at least one of the Epoxy/Fiberglas PC-7 RF circuit boards is now dead!  It did not survive the removal of the tuning capacitor.  Even using UTMOST care, the circuit trace that lead to the Mixer (Center) Section of the Tuning Capacitor wound up damaged beyond repair.  There is actually a 1/8" gap between the capacitor pad and the rest of the circuit trace.  (I'll post a picture when we have some daylight.)  It's a shame, but those are the "breaks of the game."

     I won't shed *too* many tears.  That little ceramic trimmer (C8) had been "kluged" as well.  Instead of the original triangular spring-steel mount, a standard 6-32 nut had been soldered to the foil and a long 6-32 screw had been soldered to the nut.  This was the circuit board that was in "Candidate Number Two."  I *TOLD* you it looked pretty crusty!  Looks were not deceiving.

     The GOOD news is that all of the impossible to find parts DID survive.  We already knew the tuning capacitor was bad, so it needs to be replaced anyway.  (This was the one that had a finishing nail used in the non-functioning planetary drive part of the tuning capacitor.)

     There is one more bit of good news.  I have a brand new (NOS) Virgin PC-7 Epoxy/Fiberglas circuit board available.  I guess it's time to press it into service.  Too bad I only have ONE.

     More to come.

Sincerely,

Bill Thomas

[Bill Thomas]

December 21st, 2008 - Update:  "Circuit Board Circus!"

     As promised, it's time to take a look at some of my *less* than "handy work!"  In our previous update, I mentioned that I managed to DESTROY one of the RF Printed Circuit boards.  We already know that Dynaco's circuit boards are pretty fragile, but this update will show you just HOW fragile.

     First up:  Here's a picture of the RF Circuit Board I managed to turn into "Landfill Fodder" even though I was EXCEPTIONALLY careful with the de-soldering process.  This is what NOT to do:

                   

     On the bottom of the picture, you'll see the traces that go to the three-sections of the Tuning Capacitor.  Make that TWO traces.  The middle one is destroyed!  Here's a close-up of the carnage:

                        

     GREAT job!  Again, I really DID use EXTREME care in trying to "liberate" that Tuning Capacitor.  It just goes to show you that having "parts units" available can keep you from calling the "Suicide Prevention Hot Line."  Fortunately, we have other boards available, and even one absolutely un-touched NOS board available (if necessary.)  I'm going to *try* to use a board from one of our other "Candidates" before I resort to using that NOS board.  The reason is simple:  I want to save it so I can use it as a pattern to churn out some NEW boards at a later date.  (I have no timetable set for actually MAKING those boards yet, but when I do, I'll let everyone here know about it, ok?)

     Ahhh, but there's MORE "great news!" (Not!)  Remember that "Candidate" with the desirable IF transformers?  To refresh your memory, here's a picture:

                   

     Looks pretty good, doesn't it?  But as they say, "looks" can be VERY deceiving.  But to understand WHY we have problems with this board, we need to look at a "problem area" with ALL of the Dynaco tube-type tuners.  Two little parts on the IF board cause SERIOUS problems.  Here's part number One:

                   

     And here's part number Two:

                   

     Gee, they don't *look* like "problem children" - they look FINE!  But again, looks are VERY deceiving.  These are 10 K 2 Watt resistors and these are actually "upgraded" parts from the original 2 Watt carbon-composition resistors used in the original FM-1 tuners.  The problem is: Dynaco's circuitry pushes these parts WAY too hard.  One of them dissipates 1.9 Watts, while the other one has to dissipate almost exactly TWO Watts of power.  Now you *might* think that it's no big deal, but good engineering practice *usually* suggests that a resistor should be rated at least DOUBLE it's expected dissipation.  That means BOTH of these resistors should be rated at 4 Watts or better!  In the FM-1 tuner, Dynaco had a rash of failures because the old carbon-composition resistors would actually burn up!  So, they went to the more "robust" parts shown above.  The trouble is, these are still Two Watt resistors.  Yeah, *they* survive, but they generate WAY too much heat and the result of all that heat brings us to the next "disaster."

     After removing those two resistors, we get a clearer picture of the damage they caused.  Here's the area under Resistor Number One:

                   

     And here's the area under Resistor Number Two:

                        

     By removing the resistors, we can see that the Printed Circuit board substrate is actually blackened from the excessive heat, this caused the boards to become TERRIBLY brittle and they developed cracks.  (I have flexed the circuit boards slightly to exaggerate the cracks for the photos.)  While you can't really see it in the photos, those two cracks continue underneath the tube socket and join together.  OBVIOUSLY, we don't want to build a tuner using this circuit board.  We want a tuner that will last for years and years without potential problems that would be nearly IMPOSSIBLE to find later on.  Using this circuit board *might* work, but it also *might* lead to serious instability problems and increase the likelihood that our finished product would drift when it warmed up, or maybe even a unit that would stop working completely when it warmed up.  Nope!  This board is now "landfill fodder" too!  I have already removed those IF transformers for use on a different circuit board.

     So you might wonder, "Isn't there any GOOD news?"  You BET!  Here's a picture of some VERY good news!:

                   

     Cleaned up pretty nicely, don't you think?  Here's the "head-on" shot:

                   

     And here's a picture of the rear of the chassis:

                   

     Here's the shield for the Tuning Capacitor:

                        

     And here's a picture of the Front Panel:

                   

     Quite honestly, I was surprised these metal parts cleaned up this nicely.  At least we have a SOLID foundation upon which to build our FIRST tuner.  Now all we need is the circuit boards to go with it.  As James Garner said in "Support Your Local Sheriff",  "I'm workin' on it!!  I hope to show you the results of that work in our next update, along with a recipe for my "secret sauce" for tuning capacitors!  Stay Tuned!

Sincerely,

Bill Thomas

[Bill Thomas]

December 25th, 2008 - Update:  "All I Want For Christmas Is My RF Board!"

     Whad'ya Know?  I GOT one!  And here it is:

                   

     This is the overall shot of our completed RF board with C1 (the main Tuning Capacitor) attached.  This turned out to be a hard-fought battle.  Of course, you already know that I toasted one previous RF circuit board when attempting to remove the bad tuning capacitor.  While that didn't happen with *this* board, there were other "issues."  Here's a closer look at the completed board:

                   

     Notice that all of the ceramic disc capacitors are standing straight up.  This is important to minimize stray capacitance that could easily make the board "un-alignable."  But we still have one potential trouble spot - that funky little adjustable dial-tracking capacitor called "C8".  Here's a closeup photo:

                                                 

     In rebuilding the RF board, I removed EVERY part *except* this little trimmer capacitor.  It is VERY difficult to install this part so it is stable and doesn't "self-adjust" due to vibration.  This particular part had been installed VERY solidly, BUT it was originally installed 180 degrees from the proper position.  Notice how the wire comes off the opposite side of the capacitor, while the silk-screen printing on the circuit board indicates a (correct) straight path from the side closest to the tuning capacitor.  Oops!  But since this came from a tuner that HAD worked in the past, I chose to leave this alone - for now!  When we get to the alignment stage, we *may* have to fix this goof, but if we're lucky, it'll operate properly even though it is installed incorrectly.  (PLEASE, Santa?)

     On this board, we also had a problem with one broken circuit board trace.  Here's a closeup picture of the repair:

                                  

     You can see where the trace USED to be, but there was a crack in the trace and it wasn't making a good connection to that capacitor.  No such problem now.  The lead from the new capacitor was used to connect to the other components.  All other circuit board traces and connections are solid, but there was another *interesting* problem with this circuit board.

     Dynaco's circuit board supplier applied a "solder mask" over the foil traces.  While this *normally* leaves exposed copper where components are to be soldered, there were NUMEROUS places where the solder mask completely covered the copper foil pads, making soldering impossible.  In "de-construcing: this circuit board, I noticed at LEAST 15 solder joints where the solder "balled-up" and made a VERY poor connection to the actual circuit traces.  I used fine sandpaper (1000 grit) to remove the solder mask at these locations so all joints are now clean, shiny and have excellent integrity.

     In our previous update, I mentioned my "secret sauce" for tuning capacitors.  If you've ever run onto a tuning capacitor that is electrically noisy, but none of the plates rub or touch, chances are your problem exists because the capacitor has lost its lubrication.  How can that be?  Simple.

     A tuning capacitor consists of two sets of plates; a set of fixed plates called the "stator plates" and a set of rotating plates called the "rotor plates."  The stator plates are insulated from the frame of the capacitor, but the rotor plates MUST make good electrical contact with the capacitor's frame.  Yet, they still must turn freely in order to operate properly.  In the FM-3 (as with most tuning capacitors) ball bearings are used to minimize friction, but they also minimize the electrical contact area to a few very tiny points on each ball bearing.  Add a little normal grease, and those points of contact are almost eliminated and the capacitor won't work!

     We need a SPECIAL kind of grease.  While most greases are insulators, we need one that is an EXCELLENT conductor!  Do they make such an animal?  You bet they do!  Here's a picture:

                                       

     This is my "secret sauce" for tuning capacitors.  It allows us to *carefully* clean out the front and rear bearings of the tuning capacitor and then re-lubricate them properly.  This stuff is VERY conductive, so don't smear it on any of the capacitor's insulators!  It is a lithium-based white grease with silver particles added.  That also means it isn't cheap!  This little 6.5 gram applicator costs around $25.00!  Fortunately, there's enough grease here to lubricate approximately 20 tuning capacitors.  If you need some of this stuff, it is available at Grainger Industrial Supply.  Your local store *probably* won't have it in stock, but they can *usually* get it from their warehouse and have it at the local store a day later.

     Once the ball bearings are completely cleaned, apply a small dot of this grease to the balls, and the spaces in between the balls and rotate the capacitor.  You have enough if you can *just* see a coating of gray between the tuning capacitor shaft and the frame of the capacitor.  If it begins to "ooze" out the front of the capacitor, clean it up!  You DON'T want this stuff dripping on your RF circuit board!  Apply some at the rear bearings of the capacitor as well.  If you get a reasonable coating on the bearings, it will spread around as you "tune" the capacitor and all will be well.  Again, not TOO much!  Just enough to grease the bearings for proper operation.

     That's it for our Christmas Day Update!  I hope yours was filled with joy and warm feelings all around!  In our next update, we'll cover the rebuilding of the IF circuit board, as well as our initial assembly of the Main Chassis and the Front Panel.  Stay with us - there's LOTS of "Fine Tuning" to come!

Sincerely,

Bill Thomas

[bregez]

Bill,
That chassis looks fantastic. 
Did you use a common brillo pad to clean them up like on the SCA-35 rebuild?
Have a Merry Christmas!
Brad

[Bill Thomas]

Hi, Brad!

     Yep!  SOS pads plus a solid workover with Wright's Brass Polish.  It took awhile, but things turned out a lot better than I *thought* they would.  If you look closely, you can still see some staining on the top of the main chassis, but it is minor.

     I'm about halfway through the IF board as we speak.  I won't have any "before" pictures of the blank PC board, but the "after" pictures will follow sometime Tomorrow.  Hopefully, we'll be tuning in some stations by Friday night.  Then I'll begin the build on the second tuner.

Sincerely,

Bill Thomas

[Thol]

Bill: Outstanding as usual Bill. I never thought I'd see the FM-3 get this kind of detailed coverage. I think that your introduction is a great service to the Dynaco community for this reason: anytime some attention is brought to a vintage unit, the resale punters start jacking up the market value on available specimens. Your article clearly points out the problems associated with putting your hopes into any one unit that needs restoration. Using two or even three units will be necessary in many cases. Your descriptive approach will provide a sobering moderation for any such commercial activity. Decades ago, van Alstine was already calling attention to some of the points you covered. Since then, time has enlarged the same faults in so many examples.

I agree with your assessment of the FM-3 entirely. So much about the tuner can be bettered by even modest solid state units — including a number of them from the same period. (This is usually evident when all their caps have been changed out.) But, nothing exceeds the musicality of the Dynaco. This tuner literally served me as a teacher for years, because it presented music genres that I neither liked nor understood in such a way that I listened and learned to appreciate. I say that after running one continuously from 1971 until 1992 ... and in some years on and off since then. And BTW, those more than twenty years just mentioned involved just one factory-wired unit that saw NO service or adjustment of any kind!   Cheers Lorne in Sendai, Japan 

[Bill Thomas]

Hi, Lorne!

     It is always a true pleasure hearing from you.  For one, you share this "sickness" for Dynaco gear that I caught years ago, but you have also "been there and done that" with these units.  I think we need to form a "12 Step Club!"

     Regarding Frank Van Alstine's article in "Audio Basics", there is no question that Frank covered *almost* every detail regarding "Keeping the FM-3 Tuner Alive."  As usual, we owe Frank SO much for sharing his knowledge and insight AT NO CHARGE!  What a truly magnanimous gesture!  (The only thing he *didn't* cover in his original article was covered by the "follow up" letter from Carlyle Rabe, which Frank also published.)

     I wrapped up the IF board earlier this evening and am now tackling the Multiplex board - the most fragile of ANY printed circuit board I have seen in ANY Dynaco gear.  If you just *look* at it funny, traces will mysteriously lift from the substrate.  The board I chose was apparently built by someone who owned stock in a solder company!  He wasn't very careful to make certain each joint was properly made, however.  I wish I could have snapped a few photos, but the weather here has been simply terrible and I am on a VERY tight schedule on this unit.  I really NEED to complete the first unit before the weekend is out and start the "burn-in" process on Monday because this really NEEDS to be shipped to a gentleman by Wednesday.  Hopefully, I'll be able to spend a little time on the alignment procedure.

     There is ONE suggestion for anyone who is attempting to rebuild one of these tuners.  Make SURE that each of the tuning slugs in the transformers is not "frozen" in place BEFORE you install the transformers.  If you have to remove one later, chances are the IF or the Multiplex board will be ruined!  You can also check the integrity of the coils with an Ohm meter BEFORE you install one that might be open.  "Measure twice - Cut Once!"

     Well, time to round up the resistors and capacitors.  I also have to spend at LEAST an hour just cleaning up the leftover flux and crud on the circuit board, so I'd better get crackin'!

Sincerely,

Bill Thomas

     

[Bill Thomas]

December 27th, 2008 - Update:  "In the Immortal Words of Mr. Loaf..."

     The title of this update refers to a review that appeared in the New York Times.  When Meat Loaf made his initial appearance on Broadway, the New York Times had *some* difficulty in deciding how to refer to him.  I'm sure there was quite a bit of consternation over THIS one, but the reviewer *finally* decided to refer to him as "Mr. Loaf."  (By the way, the review of "Mr. Loaf's" performance was EXTREMELY positive - as it *should* be!)  "Mr. Loaf's" breakthrough recording was, of course, "Two Out of Three Ain't Bad" which happens to describe our current "state of affairs" quite nicely.

     We've already covered the completion of the RF Circuit Board.  Now, here's a picture of the (almost) completed IF Circuit Board:

                   

     There's a reason there are a few parts missing from the upper-left part of the board.  There are two coupling capacitors and one PEC module yet to be installed.  The reason they are "un-installed" is that I may have to "juggle the values" of the coupling capacitors a bit.  The PEC module is not installed because I will be replacing the stock part with a replacement that uses different values because THIS tuner is going to be "traveling abroad."  I will be testing it using a new stock PEC module, but it will be "tack soldered" in with full component leads.  Once testing is complete, the replacement will be permanently installed.

     The modified PEC replacement will give the L+R main channel of the tuner a 50 microsecond de-emphasis curve, rather than the usual 75 microsecond curve.  This will make it sound a bit *bright* when listening to US stations, but everything will sound perfectly normal once this tuner winds up in its new home in England.  (We'll cover the construction of the module in a later update).

     If I were building an FM-1 Monaural tuner, we could stop here, but this one will be an FM-3 Stereo tuner.  That means we need one more circuit board.  Here's a picture of the board under discussion:

                             

     This is a picture after removing all the passive components (except the two transformers and the tube sockets).  This is also after spending over two hours cleaning and cleaning and CLEANING a TON of crud, excessive solder and leftover flux.  Whoever originally built this board must have had NO soldering experience whatsoever.  There's a *little* more cleaning to do, but we're almost ready to begin populating the board with new parts.

     There's light at the end of this tunnel and I don't hear a train coming!  As "Mr. Loaf" once sang,  "Two Out of Three Ain't Bad" see?

                   

     In our next update, we'll cover the completed Multiplex board as well as the next step:  Putting it all together!  There's a LOT of fine tuning to come.  Stay with us!

Sincerely,

Bill Thomas

[Bill Thomas]

December 30th, 2008 - Update:  "Now Appearing at Your Local Multiplex..."

     This will be a rather short update covering the construction of the Multiplex Adapter Board for our FM-3 tuner.  Rather than keep you in suspense, here's a picture of the final product (with two small exceptions):

                             

     You'll notice a few "upgrades" to our Multiplex board.  The Output coupling capacitors have been increased in value from 0.1 uF to 1.0 uF.  This will help our tuner deliver much better bass response.  Also note that while I had planned to use metal film resistors throughout, I ran low on a couple of values and my local parts store was also out, so there are three carbon films on the board.  (I just wanted to let you know - in the interest of "full disclosure.")  Carbon films are substantially less noisy than typical carbon composition resistors, so our finished tuner should still sound better than a "stock" unit.

     There IS one area where tighter tolerance resistors are REALLY important.  For BEST stereo separation, the four 47K resistors associated with the diode bridge should be matched as closely as possible.  The actual value of the resistors can be off quite a bit, but they really DO need to be VERY closely matched.  Here's a close-up of the resistors in question:

                             

     As you can see, we wound up using four 1% 46.67K resistors - WELL within the "margin of error" of our original 10% carbon composition resistors, but the IMPORTANT thing is that they are all absolutely "dead-on" identical!

     If you'll look up and to the left, you'll notice that the PEC modules haven't been installed yet.  That's because we are modifying this tuner for proper decoding of European FM standards.  This means we will be building our own PEC modules.  In the interest of better frequency response, we will be using Sheldon Stokes PEC module "upgrade" for our tuner.  Here's a picture of one of the modules designed for the US de-emphasis curve:

                             

     Not much to see is there?  OK, here's a look without the covering:

                         

     In order to conform to European transmission standards, we need to reduce the  3 angled capacitors from 510 pF, down to 340 pF.  By reducing the capacitance by a third, we will also reduce the de-emphasis time-constant from 75 microseconds, down to 50 microseconds - in other words, by one third.  The only problem is:  340 pF capacitors are an "oddball value" - NOBODY makes them!  So, to get the right value, we'll have to combine two capacitors in parallel in order to get 340 pF!  In our case, we'll use a 100 pF in parallel with a 240 pF and *VOILA!* - 340 pF!  Multiply that by a factor of six, and we'll have our European de-emphasis curve taken care of!  It may not be completely "elegant", but it WILL be accurate!

     Notice anything else missing on our completed boards?  Yep!  Those grounds for the tube shields are missing!  I WILL install them when I wire the adapter board into the chassis.  I just didn't want to heat, and then REHEAT the circuit board.

     By the way, those 1.0 uF capacitors are quite a bit bigger than the original 0.1 uF parts, To make SURE things don't "short out", the four capacitor leads have been insulated with *tiny* tubing.  Take a look at how close things are around the Left Output capacitor:

                             

     And here's a look at how close things are at the Right Output capacitor:

                               

     All things considered, it looks like this will be a pretty nice tuner.  All we need to do now is "Wire it all together!"  We'll do that AND we'll correct a mistake Dynaco made when they designed this unit "back in the day."  That little "mistake" meant that nearly every FM-3 tuner has more hum than it needs to.  This one WON'T!

     There's still a LOT of "fine tuning" ahead.  Don't give up now, we're in the "home stretch!"  Stay with us!

Sincerely,

Bill Thomas

[Bill Thomas]

December 31st, 2008 - Update:  "Creatively Ignoring Construction Instructions"

     The FM-3 Construction Manual suggest wiring the bulk of the connections to the EMM801 tube socket on the front panel when attaching the Front Panel.  They do this by installing wire "stubs" in some of the eyelets on the IF strip board.  Unfortunately, this leads to a pretty messy outcome at the tube socket, so throwing all caution to the wind, I have decided to attack things from a different direction.  Here's what I mean:

                                       

     It gets pretty crowded around the front of the IF circuit board, but with care (and a little luck) we *should* be ok.  The end result will be a MUCH neater wiring job at the EMM801 socket.  Here's a closer look:

                             

     The heat-shrink tubing adds a little extra "insurance" against short circuits due to socket pins touching.  Looks pretty decent.  I'll let you know how this "different tack" works out!

     Now, here's something you won't see every day.  Here's a NOS Volume Control-Stereo/Mono switch assembly.  Solder hasn't touched this assembly - Yet, but it soon will:

                   

     Now, here's a picture of the Main Chassis with all our circuit boards installed:

                   

     If I didn't know better, I'd say this is *beginning* to look like a completed tuner!  Of course, looks are often deceiving.  Here's a picture of the underside of the Main Chassis at this stage:

                   

     All we need now is about 12 feet of wire (properly installed, of course) nine resistors, fourteen capacitors and a bit of alignment and we'll have us a tuner!  We'll cover all that pretty soon, as well as our "fix" for Dynaco's *teensy* little "goof" that caused excessive hum.  Stick around - the BEST is yet to come!

Sincerely,

Bill Thomas

[avahifi]

Question Bill; do you have a source for the necessary Germanium diodes used on the MPLX board?

Frank Van Alstine

[Bill Thomas]

Dear Frank,

     I had a matched set of four in my "parts stash" and am working on another source for more.  My problem is going to be how to properly match sets of four.  My brother has an old H-P semiconductor curve-tracer *somewhere* in storage, but he is out of town for another week.  I do have some "culls" available from FM-3 "parts units" if you have an immediate need for a set.  Just let me know.

Sincerely,

Bill

[rlee8394]

Frank,
Check out NTE110MP on this page:

http://www.nteinc.com/Web_pgs/GenPurpD_R.html

This is what Chauncey from FM3 Zone uses in his upgrade kits. They seem to work well in my FM-3.

Ron

[salb203]

Hi Bill,
Your timing is perfect as I have 2 FM-3's I want to rebuild.

I also happen to have a unbuilt FM-3 in my posession including the 2 errr, make that 1 Telefunken 12AX7, I dropped the one of the 12AX7s when I took it out of the box and sheared the tip off causing a vacuum leak, I am still sick to my stomach when I think of it...

Sal