[Bill Thomas]

     Thanks, Lee and Joe!

     Joe, I've been signing the praises of Nev-R-dull in the rebuild articles as well, but Wright's Brass Polish actually works quicker and better than Nev-R-dull on the knobs.  That's why I made such a big deal over it, specifically.  Nev-R-dull is my choice for the Stereo 70 chassis', but Wright's gets the nod for regenerating those knobs.

     Of course, this is just *my* humble opinion.  I am ALWAYS willing to investigate other solutions.  The idea is to pool our collective knowledge "for BEST results", right?

Sincerely,

Bill Thomas

[k-man]

I've been slowly rebuilding my SCA35 the last year or so and am following your project with great interest.  How did you get the chassis so clean?  I cant figure out what type of metal it used but it's very hard to remove oxidation from.  Does yours have a ground wire from your filter caps going to the line level inputs and grounding at the chassis there?  From what I've read the SCA-35 is the only one where they went to this strange grounding scheme but it's seems to work good so long as you don't add a three prong power plug.

[Bill Thomas]

Dear k-man,

     The chassis parts are made from cadmium-plated steel.  You'll be really surprised about the method I used to clean the metal parts.  Total cost? Under a Dollar!  Common SOS pads and water!  Of course, the chassis has to be totally stripped of parts before doing this, but it produced the BEST results with the LEAST amount of effort.  It won't fix corrosion problems, but it WILL make the parts shine where the plating is still intact.  Some staining is reduced or removed, but deeper staining will remain.  It always pays to start with the best metal parts you can find.

     Yes, the grounding arrangement *seems* a bit weird, but if you follow it around the unit, it's not *quite* as crazy as it seems.  The common "audio ground point" is indeed at the RCA Line-Level jack field.  This connects (via the black ground wire) to the mounting tab of the first can capacitor, which also happens to be the ground point for the center-tap of the Power Transformer.  This is the main grounding point for the High Voltage Power Supply as well.  The grounds for the Output Boards also connect to one of the first can capacitor mounting tabs.  These two grounds are kept totally separate and also connect to the front panel ground points for each channel on the balance control.  The ground for the equalized preamp board comes from the second can capacitor mounting tab.  Another mounting tab on this capacitor is connected to a mounting tab on the FIRST can capacitor, so "ground is still ground."  The grounds for the low level inputs come from the equalized preamplifier circuit board.  The ground for the Output Transformer feedback network goes to the terminal strip ground.  (It isn't quite as important to ground this at the can capacitor due to the levels and impedances involved.)

     NEVER replace a two-wire Power Cord with a 3-wire Power Cord on any of the Dynaco equipment that uses unbalanced audio connections.  You will most CERTAINLY wind up with a ground loop, once all the associated source components are connected to it.  (Of course, you can STILL wind up with ground loops anyway, but the chance for serious hum is MUCH less with a 2 wire Power Cord.

     Hope this helps.

Sincerely,

Bill Thomas

[Bill Thomas]

November 12th, 2008 - Update:  "Remember the Main (Chassis)!"

     "Life is what happens to you while you're busy making other plans!" - John Lennon.  Well, "Life" has been really HAPPENING around here!  But now that there's a *bit* of a lull, let's bring things a bit farther along with our SCA-35 rebuild project.

     As I mentioned in our last *real* update, there's a good deal of wiring involved around the four Output tube sockets.  Here's a picture of the completed wiring:

                   

     Things get pretty crowded around those little tube sockets.  Use EXTREME caution to make sure you aren't going to have intermittent short circuits due to the closeness of the tube socket lugs.  The black and green twisted pairs are for the tube filaments.  They are the HARDEST parts of this wiring to keep from touching.  One word of advice:  Add another 1/4" to the length of the wires Dynaco specified for these connections.  It will allow you to more closely route the wires according to the Dynaco pictorials for minimum hum.

     The Yellow wires connect the Cathodes of all four Output Tubes together.  Then the Cathode Connections are returned to the last section of the first can capacitor (and the small additional capacitor), as well as the 95 Ohm resistor going to the mounting tab of the capacitor.  This provides the necessary negative bias Voltage for the Output Tubes.  But, it depends upon all FOUR Output Tubes being installed in order to derive the proper Voltage.  The Capacitors across the 95 Ohm resistor actually provide TWO functions.  First, they act as a filter capacitor for the bias Voltage, not unlike the two filter capacitors in the Stereo 70 bias supply.  The capacitors also provide "audio decoupling" of the Cathodes.  In other words, while the DC Voltage of the Cathodes winds up around 14 Volts, the AC Impedance to ground is kept low because of the 120 uF of capacitance.  This increases the gain of the Output Section.  So, the Cathodes of the Output Tubes are at +14 Volts.  The grids of the Output Tubes are returned to ground via the grid resistors (470 K each).  Since there is no grid current, those resistors have no Voltage drop, which puts the grids at NEGATIVE 14 Volts with respect to the Cathodes.  In other words, proper bias for normal operation.  With these values, each Output tube is drawing just under 37 mA each.  That's just under 74 mA for each pair.  That's under 148 mA for all four Output tubes.  Pretty neat, huh?  And no bias adjustments to worry about.  As the tubes age, the current draw will gradually decrease, but as that happens, the bias Voltage becomes a little less negative, so the tubes conduct "heavier" restoring the proper current draw AND the proper negative bias Voltage.  Of course, EVENTUALLY the tubes will not conduct enough; even with significantly less negative bias Voltage.  At THIS point, it's time to replace the Output tubes, otherwise you'll be treated to the sight of all four tubes glowing with cherry-red plates!  Remember, all four Output tubes should be matched as closely as possible for proper operation.

      With the Output Modules completely wired in the Main Chassis, here's a picture of our wiring progress on the Main Chassis so far:

                                                  

     If you look at the black and green twisted pairs of wires going to the Phono Preamp Circuit Board, notice that they are kept  away from the circuit traces as much as possible to minimize hum.  The connections for all the tube filaments are complete, but there is more to connect to the filament windings of the Power Transformer at the terminal strip.  When we finish the wiring, those four terminals will be PACKED!  (The actual wires from the Power Transformer aren't REALLY connected yet, they are just routed to the terminal strip area until we get to the final connections at the terminal strip.)

     We're making good progress now.  Here's a picture of things "topside" - it's *beginning* to look like a real amplifier:

                 

     Now, all we have to do is slap the front and rear panels on, add the selector switch, wire it all together and we've got an update!  And our NEXT update will follow tomorrow.  Honest!  Don't miss it!

Sincerely,

Bill Thomas

[Bill Thomas]

November 12th, 2008 - Update Two:  "Time For a Panel Discussion!"

     Yes, Boys and Girls, it's time for us to talk about panels - Front and Rear!  Let's get into it by attaching the Front Panel to the Main Chassis and wiring it in.  Let's "cut to the chase" and show you the end result of this step:

                             

     Wiring in the Front Panel is actually pretty easy since there are only two shielded cables and two green wires from the Pilot Lamp to connect at this time.  The two black wires from the Power Switch route under the cable clamp and head to the back of the Main Chassis.  We'll connect them when we attach the Back Panel.  The two shielded cables I mentioned are the audio feeds to the Output Modules.  But, these are pretty important because they provide the ground connections for the Left and Right Channel Circuitry on the Front Panel.  We already looked at the connections at the Balance Control.  Now, let's take a look at the other ends of those two shielded cables.  First, here's the connection at the Right Output Module:

                                       

     If you'll look closely where the Shielded Cable is soldered to the Output Module, you'll see three wires coming out of the shielded cable.  One is Red and connects to Eyelet #7.  The other two wires are Black and the shield connection (inside some clear shrink-wrap tubing).  The Black wire is the Low or Ground side of the audio connection from the Right Channel audio circuitry on the Front Panel.  The Red wire is the "Hot" lead.  The Shield wire is connected at this end only.  The thicker Black wire comes from the Mounting Tab on the First Can Capacitor.  That's where our "Ground" comes from.  The Green wire that is soldered to Eyelet #2 is the feedback connection from the Output section of the module.  The Black and Green twisted pair are the Filament connections.  The empty Eyelet #1 will be connected when we attach the Rear Panel.  The other Shielded Cable in the picture is the wire to the Left Channel Output Module.  Here's how IT is connected:

                                   

     Looks a lot like the connections in the previous photo, doesn't it?  That's because it IS the same.  It just goes to the Left Channel audio circuitry on the Front Panel.  Here's a picture that shows why the PEC modules are stacked on top of each other:

                         

     Not a whole lot of extra room between the PEC modules and the Main Chassis shield.  But that's NOTHING compared with the lack of room  at the Selector Switch!  Take a look:

                                       

     Part of the preparation for wiring in the Selector Switch involves soldering in TWELVE wires from the chassis Eyelets before the Selector Switch is mounted.  (You could NEVER solder them AFTER the switch is installed!)  One "construction hint" that may help you "do the deed" is to add 1/4" of length to each of the wire lengths specified in the manual.  It makes a nearly IMPOSSIBLE job *barely* possible!  We've deviated from the manual in one other way:  Rather than using a twisted pair of wires for the connections to the switched equalization circuitry, we've used two more shielded cables.  Yes, space is at a premium, but the shielded cables are MUCH more tolerant of routing "differences" than the twisted pairs are.  (And they won't pick up any additional hum either!)  Those two "Orange Drop" capacitors are part of the switched equalization circuitry.  Yes, they're bigger than I would like, but there's *just* enough room for them.

      Here's a picture of the Rear Wafer of our NOS Selector Switch:

                                             

     While it IS a brand NEW, never used switch, it was pretty badly oxidized after sitting "on the shelf" for 44 Years!  But it certainly cleaned up quite nicely, didn't it?

     Gee, I seem to remember saying that attaching the Front Panel was EASY!  Yeah, RIGHT!  Wiring in the PANEL is easy, but that Selector Switch is a BEAR to deal with!  And we'll have to have MORE dealings with that "bear" when we wire in the REAR Panel.  We'll cover that in our NEXT update coming up tomorrow.

     We are REALLY close to "Firing it up" now.  One last panel to go and we're THERE!  You won't want to miss our next installment.  It'll REALLY "deliver the goods!"  ('Bout Time!)

Sincerely,

Bill Thomas

[Bill Thomas]

November 13th, 2008 - Update:  "Advance, to the Rear!"

     Well, we're down to the final assembly and wiring of our SCA-35:  The Rear Panel!  Here's a picture of our current "nemesis" - now fastened to the Main Chassis:

                   

     It *looks* innocent enough, but to get to this stage you almost need to grow another pair of arms!  The reason is, you have to wire most of the Rear Panel BEFORE fastening it to the chassis!  But here's a tip:  If you connect the black ground wire from the RCA Jack Field, you can then "finagle" the whole assembly on TOP of the inverted Main Chassis, and it'll STAY there while you complete the wiring.  More productivity - Less "cussin'!"  I'll buy that ANYTIME!

     Here's a picture underneath our Main Chassis with the Rear Panel attached:

                   

     The wiring to the Speaker Output Terminals is *probably* the most challenging; mainly because we're reusing original Dynaco Transformers and the leads of the rear transformer had already been pre-cut to 3"!  But with enough patience, and understanding, (and some SERIOUS "CUSSIN'!") it all went together quite neatly.  (I need some NEW cuss words now!)

     Once the Output Transformer wiring is complete, you can THEN mount the Rear Panel to the Main Chassis.  You DID remember to tie-wrap the Shielded Wiring to the RCA Jack Field, right?  No?  Well, you're in good company, I forgot too!  Here's why this is important:

                             

     At this angle, it's pretty easy to see why you NEED to "clean things up" with the wiring to the RCA Jack Field.  You can *barely* see the wiring to the Left Channel, but the Right Channel wiring is REALLY buried between the Rear Panel, and the back of the Main Chassis.  You can mark the wires, or just use your Ohm Meter to sort them out later, when it comes time to wire them to the Selector Switch, but a few strategically-placed cable ties really help to keep things together, neatly.

     One area where we deviated from Dynaco's original instructions has to do with the wiring of the AC Receptacles on the Rear Panel.  Take a look:

                             

     In the original instructions, Dynaco wired the receptacles opposite each other.  Now, the Neutral is on the same side on BOTH Receptacles.  Also, our new fuse holder had the side lug on the opposite side.  No biggie!  Another inch of wire solves THAT "issue!"  The Power Cord is an original Dynaco cord that has been cleaned and reconditioned.  Rather than subject this "busy" wiring area to additional stress, I used a strain relief, rather than a grommet.  This also meant that I didn't need to tie a big knot in the Power Cord.  It's just a *little* neater that way.  Let's go Topside!

     Here's a picture of the shielded wiring to the Selector Switch:

                             

     Again, it's easy to see why you want to keep the shielded wiring together with cable ties.  We can ALSO be thankful that the connections are on the TOP of the Selector Switch!

     Hey!  Guess what!  We've wired an amplifier!  Here's the "overall" picture from the top:

                  

     This picture was "posed" with a couple of mis-matched 12AX7's, but the rest of the tubes are PRIMO for this particular amplifier.  The 7199's are NOS RCA Black Plates and the Output Tubes are a matched quad of NOS GE 6BQ5's.  (We'll go into further detail in our FINAL installment.)

     We've still got more work to do before it's REALLY a "wrap!"  Take a look at our Face Plate in "as found" condition:

                             

     We'll show you how this all cleaned up and give you a report on what happens when we "give it the smoke test!"  (That's when you turn it on and see what "smokes!")  This is all coming up in our FINAL Update, later tonight!  (Aren't you excited?  *I* am!)

     Stay Tuned!

Sincerely,

Bill Thomas

[Bill Thomas]

November 13th 2008 - Update Two:  "The Finishing Touches!"

     At LONG last, our "Final (mostly) NEW Dynaco SCA-35 Integrated Amplifier" is complete!  I won't keep you in suspense.  Here's how our Face Plate cleaned up:

         

     Yes, it's the same Face Plate!  It's not absolutely *perfect*, but it's a FAR cry from what we started with.  Notice how nicely those old die-cast knobs cleaned up too.  Wright's Brass Polish is to blame.  GREAT stuff!  This *obviously* came from a well-used amplifier, since some of the lettering around the Power Switch is worn, but all things considered, this is one mighty pretty amplifier.  Take a look from a higher angle:

                   

     Trying to get the "knurling" on the knobs clean is quite a challenge, but the end result is well worth the effort!  The Pilot Lamp amber "jewel" is a NOS part from my Dynaco "parts stash" since the original wasn't exactly "pristine."  THIS one absolutely IS!

     Now, here's a picture from an even higher perspective so you can see the "innards" through the perforated cover:

                   

     Not bad at all.  I don't know about you, but *I* wouldn't be the LEAST bit ashamed to display THIS unit in a "Vintage System!"  And let me tell you, this amplifier simply REEKS with that "Vintage 6BQ5/EL84" goodness!  So let's talk about what we discovered when we started bringing the amplifier "back to life!"

     Once the amplifier was wired, I installed a 1 Ampere fast-blo fuse and with all tubes removed, I g-r-a-d-u-a-l-l-y began applying Voltage with a Variac.  Since the SCA-35 uses silicon diodes, the High Voltage supply will begin delivering "juice" with even the LOWEST Voltage from the Variac.  This made it easy to see just how well the Filter Capacitors were working.  With no load from the tubes, there is no current (or *nearly* no current) drawn from the High Voltage Supply.  This causes every section of the Can Capacitors to charge up to (nearly) the same Voltage.  There was less than a 1 Volt difference from the First capacitor section to the last.  Since these capacitors are really "overkill" for the SCA-35 (they're rated at 525 Volts!) we didn't have to worry about exceeding any Voltage ratings.  After "cooking" the Power Supply for awhile (and after making SURE the Power Transformer windings were delivering the proper Voltages), I powered things down and added some tubes.

     I picked up a couple of used 7199's I had lying around and a couple of mis-matched 12AX7's as well.  But, for the Output Tubes, I wanted to make SURE they were matched, so I went with a matched NOS quad of GE 6BQ5/EL84's.  A new Pilot Lamp finished the procedure.  (Boy, are those things hard to seat in such cramped space!)  Once again, I used the trusty Variac to GRADUALLY begin applying power again.  What can I say?  It all went totally uneventfully!  Everything came to life without a hitch!

     When I originally built my SCA-35 WAY back in 1965, I coupled it with a pair of AR-4x speakers.  As it so happens, I actually HAVE a pair of AR-4x speakers available so, what the heck!  Why not?  I connected them up before the first REAL Power-up, added a little audio once things were up and running, and Voila!  Suddenly, it's 1965 again!  You wanna talk about how "sound" can trigger memory?  I was STUNNED just how much I remember how this combination sounds!

     So, feeling a renewed sense of "well-being", I Powered-down and pulled the 12AX7's and the 7199's and replaced them with a matched pair of NOS RCA Black Plate 7199's from the 60's.  Then I searched my stock for the final touch:  A pair of VERY lightly-used Dynaco-branded Telefunken smooth plate 12AX7's!  When I tested them in my Hickok, they tested higher than a NOS pair of RCA gray plates.  The life test showed NO indication of any problems at all.  These are true GEMS!

     Feeling REALLY good, I flipped the Power Switch on and promptly blew a fuse!  Oh, GREAT!  What could be wrong?  Then I remembered:  I still had the original 1 Amp fast-blo fuse installed!  That means the amplifier was delivering full power earlier on a 1 Amp fast-blo fuse!  Not Bad!!!  Replacing the blown fuse with the proper 2 Amp slo-blo fuse ended the problem.  The reason the fast-blo fuse didn't blow in the original test was because I gradually brought the amplifier up with the Variac.  When I just "flipped" the Power Switch, the entire inductive "kick" hit all at once and the 1 Amp fuse simply surrendered.

     So, how does it sound?  "Heavenly" simply doesn't do it justice!  There is something truly WONDERFUL about the sound of a 6BQ5/EL84 amplifier.  There is a sense of intimacy that many other tubes seem to lose sight of.  When Roy Orbison was singing "Crying", he was right THERE, in the center of the mix - singing right to ME!  But when Norah Jones leaned into the mic, I thought my head would explode from ecstasy!  A little Elton John was next, then Randy Travis.  The SCA-35 didn't miss a lick.  Randy's and Elton's vocal gymnastics just SHINED!  I wanted MORE!

     But, it's time to conclude THIS listening session.  I have one more test to go and it's going to require a bit of "setting up" before I can comment on the Phono Preamp.  Time to drag out my reference vinyl cuts and see how our SCA-35 stacks up against the PAS-3X recordings I made earlier!

     That means, we're going to have ONE more report, but as far as I can tell (so far), the BIGGEST surprise is that there are NO surprises.  Everything just sounds GREAT!  In our last little report, I'll post pictures of the tubes (I ran out of good light this evening) and I'll give you the verdict on the Phono Preamp.  If all goes as I *think* it's going to go, *SOMEONE* is going to have a seriously DELICIOUS amplifier to play with VERY soon!

Sincerely,

Bill Thomas

[joeriz]

Man are these threads fun!  Bill, sometimes I think we should be paying you for these posts!

Joe

[Bill Thomas]

Dear Joe,

     I REALLY appreciate that Joe, but I don't want a nickel for these posts.  The only way I want to profit from these posts is to sell the completed units in the classified section.  Actually, that is a CRUCIAL part of the whole process.  Each unit that is sold generates the necessary funds to head into the NEXT "regeneration project."  The "Construction Chronicles" are simply a way for me to do my part to help other Dynaco fans get their gear up and running again.

     As I have mentioned, I'm "clearing out my closet" to get rid of dozens of Dynaco units.  But since these units are in varying states of decomposition, I simply can't "dump 'em" as-is on potential new owners.  It would be HORRIBLE to sell someone a unit that is just going to tarnish Dynaco's reputation and leave a bad taste in someone's mouth regarding Dynaco gear.  They deserve MUCH better.  (And quite honestly, my personal standards won't allow me to just dump garbage on someone.)

     The Hi-Fi Industry has changed SO much since those days.  Many parts are now IMPOSSIBLE to find.  I am trying to show people how to repair some of the original parts (like selector switches and the like) and how to "improvise" using parts that are currently available, without compromising the original design (unless the unit in question is profiled with one of the "upgraded" circuits from the aftermarket.)

     Granted, I DO have a bit of an advantage, since I have quite an inventory of original NOS Dynaco parts, but even if Radio Shack is your ONLY local source for electronic parts, quite a lot can be accomplished.

     I just hope folks enjoy these "rebuild chronicles" whether they have Dynaco gear, or not.  While I DO try to display the process, I also try to be completely truthful (especially regarding my own "stupidity" as it surfaces) in EVERYTHING I do.  It's a matter of personal integrity and as we all know, integrity takes a LONG time to establish, but it can be lost in an instant.  I think most people are getting tired of the excessive "hype" and "stretching of the truth beyond all reason" that we are "hammered" with every single day.  I hope enough people will appreciate the "honest approach" instead.

     That's MY story and I'm sticking with it!

Sincerely,

Bill Thomas

[Bill Thomas]

November 18th, 2008 - Update:  "All Good Things MUST Come to an End!"

     "It's the same with the 'Wildwood Weed'..."  Wait a minute!  THAT'S not what we're talking about here!  We're talking about our SCA-35 project: "E Pluribus Unum!"  And after MANY delays and interruptions, we are FINALLY finished!

     I mentioned that we were going to stock this amplifier with a couple of VERY desirable tubes.  I wasn't kidding!  Here's a picture:

                             

     These are Dynaco-branded, "VERY lightly-used", Telefunken smooth plate 12AX7's and we're stuffing them in our SCA-35's Phono Preamp section.  (You'll notice they were made in WEST Germany.)  Here's a picture of a *positive* identifier:

                   

     This little "diamond" is formed in the glass on the bottom of the "bottle" between the tube pins.  It's pretty hard to "fake" this identifier.  It's also impossible to fake the "magic" these tubes provide.  I went through my stock of "pulls" from several PAS preamps to find the *best* (and least used) of the Telefunken 12AX7's in my collection.  These test EXTREMELY closely and the transconductance figure is substantially higher than a pair of NOS RCA gray plate 12AX7's.  These are BEAUTIFUL tubes and they sound just as beautiful.

     So, how does the Phono Preamp sound?  Pretty darned nice!  No, it's not *quite* as nice as our "corrected" PAS-3X preamplifier (If you didn't get a look at it, here's a link to that project:http://www.audiocircle.com/index.php?topic=58900.0), but it certainly DOES sound EXTREMELY nice.

     Back "in the day", Dynaco advertising tended to suggest that the SCA-35 made the *ideal* system for College Students.  I couldn't agree more.  Couple this amplifier with a pair of high-efficiency speakers and the typical dorm room will have MORE than enough volume to drive folks out of the room!

     The SCA-35 amplifier is NOT without compromises.  For one thing, unlike almost every other Dynaco amplifier, the SCA-35 *does* have a *teensy* bit of residual hum, since the filaments of the Phono Preamplifier tubes are supplied with AC, rather than DC (as in the PAS-3X).  But the hum-adjust potentiometers allow the user to reduce the hum to inconsequential levels.  You *might* hear it if you put your ear right next to the speaker with the Volume Control WAY up, but at normal listening levels, it won't intrude in your musical enjoyment in the slightest.

     One other thing to mention is that it is somewhat easier to hit the overload point with the Phono Preamp section.  But the SCA-35 is designed to "compress" rather than "clip" the audio past the point of overload.  In a "real-world situation", you'll have a hard time finding a phono cartridge that will hit that overload point.  I'm not saying it's *impossible*, but even with my HIGHEST output cartridge, it never became a problem.

     The reason for all of this has to do with the topology of the equalized preamp section.  Dynaco actually used a bit of Positive Feedback to increase the gain of the Phono Preamp section in order to have enough gain to drive the tone control circuitry.  It's a VERY clever combination of Positive Feedback for gain and Negative Feedback for the equalization circuitry.  The end result is a truly musical Phono Preamp section.

     The SCA-35 Line Stage isn't the most sensitive, so you may find yourself raising the Volume Control a bit higher than you might on other Integrated Amplifiers.  But the *upside* is that it is pretty hard to overload the Line Stage unless you're really TRYING to.

     All in all, the SCA-35 is a truly remarkable amplifier.  No, it's not the greatest, nor the most powerful, nor the most sensitive of amplifiers, but what it DOES do is make about 33 Watts of BEAUTIFUL music with a minimum of noise and distortion.  Dynaco may have made some compromises to hit a price point, but they did everything possible to make SURE they didn't compromise the MUSIC.  (They NEVER did!)

     So let's recap.  Remember where we started all this?  Here's the picture of the "starting point" of this amplifier:

                             

     And here's how we finished up:

                   

     Here's where the "guts" started out:

                             

     And here's a look at our final result:  (Well, MOST of it, anyway.)

                                       

     To fit SO much "tube goodness" into a chassis that is only a little deeper than a PAS-3X preamplifier was a "magic act" that needed no encore.  Perhaps that's why Dynaco never made another tube-type Integrated Amplifier.  They didn't NEED to.  THIS one was "Good Enough" to stand the test of time!

     Thanks to everyone who has been following our saga, and a *special* round of thanks for all the wonderful comments.  This has truly been a "blast from the past" for me.  The SCA-35 was my very FIRST Dynaco kit back in 1965.  To be able to "recapture the moment" (at my "advanced age") served to show me just how important our "formative experiences" are in this "obsession" we call "Hi-Fi!"

Sincerely,

Bill Thomas

[bregez]

Thanks Bill,
Some of your tips and advice in this post have proven invaluable in my attempt to rebuild a PAT-4.  Your workmanship is truly top notch
Brad

[Bill Thomas]

Dear Brad,

     THAT is the kind of result I have always hoped for.  If these "Rebuild Chronicles" can help others restore their Dynaco gear back to good operating condition, then it is all worthwhile!  Thanks for the comments on the build quality.  It's always nice to hear, but YOU are the one who deserves an "attaboy" for tackling your OWN "project."  When you get finished, snap a few pictures and let us see your results too!

Sincerely,

Bill Thomas

[bregez]

Bill,
The project is taking longer than I anticipated.  The solder used by the original builder requires lots of heat and falls off in clumps!  I am trying to get every last bit of this old solder off so it doesn’t contaminate the new solder joints.  All components needed replacing as the resistors have drifted and the capacitors have leaked.
Once the project is complete I will post a few pictures.  The main lesson I have learned is restoring a stereo component is a lot more work that building a new one from scratch.
Thanks again,
Brad

[kurtbauer]

Hi Bill,

This project was really fun to watch.  I just rediscovered it whilst looking for a good choice for coax or shielded input cables.  I'd like to cut down on the crosstalk on some of my DIY equipment. 

What shielded cable are you using here?  How did it sound?  Was it worth the hassle? 

The few in-the-box terminations I've done don't look anywhere near as good as yours!

Thanks,
KB

[Bill Thomas]

     The shielded wire is nothing fancy.  It is a generic equivalent to Belden #8451.  It's a 2 conductor, 24 ga. stranded cable with full foil shield and a stranded drain wire.  In places where only one conductor is used, the second conductor is simply slid out from the jacket.  If solid conductors are more to your liking, the Belden equivalent is #8450.

     Again, this is nothing fancy.  We used to use this stuff frequently when wiring in audio consoles at recording studios many years ago.  There are much better cables available today, but this goes under the heading of "good enough" for the purpose.

     As for sound quality, it is an improvement over the unshielded wiring.  Crosstalk is reduced by a significant margin.  The capacitance of the cable is not especially low, however; it did not appear to cause any significant "tilt" in the high-frequency response in high-impedance areas of the unit.  Was it worth the hassle?  I *think* so.  You should be advised that it does not totally ELIMINATE all crosstalk because of other factors in the original design of the SCA-35.  But it definitely improved the situation, so I DO think it was worth the trouble.

     Hope this helps.

Sincerely,

Bill Thomas

[orthobiz]

Is this unit for sale? Spoken for?

Paul

[Bill Thomas]

Dear Paul,

     Sorry, this one has already been sold.  However, I am currently searching through my "Dynaco Parts Stash" for another set of controls.  I am ONE tone control away from having one more complete set of NOS controls and I *think* I have that last control (somewhere) in this *mess* of parts.

     If you'd like to talk about building another one, feel free to e-mail me at nostubesforyourdynaco@gmail.com.  (We really shouldn't discuss "items for sale" here, since this is a non-commercial section of the 'circle.)

     I *can* tell you that I will only be able to come up with two more of these units, and only ONE of them will feature all NOS controls.  The other one will have to be assembled with "used but good" controls.

Sincerely,

Bill Thomas

[kurtbauer]

Thanks for the background on the cabling.  It's really helpful.  On a related note, can you tell me how you terminate the coax?  I tried to glean your method from the photos but no dice. I've also been searching my fingers off but can't seem to find it.  I'm thinking you simply solder a wire to the braid with heatshrink in key locations and that's it.  But what do I know?!?!

Secondly, I think I've got a used, working SCA-35 control switch around here if it's of any use to you.  Volume and balance too. I'd be happy to send them your way.  I know you're looking for NOS parts but let me know if you'd like me to dig them out.

Kurt

[Bill Thomas]

Dear Kurt,

     Since all the wires in the shielded cable are stranded, I tin the length of the exposed drain wire and then use small heat-shrink tubing to insulate it.  I then use a larger piece of heat-shrink tubing over the end of the jacket of the cable to "make it pretty" and hold everything together.  Since the drain wire is *usually* only connected at one end, at the other end I wind up cutting the drain wire flush with the stripped jacket of the cable.  Then another piece of heat-shrink makes the other end neat as well.  But, it explains why you will see three wires at one end, and only two wires at the other.

     While it probably isn't *completely* necessary to insulate the drain wire, I think it is better to be safe than sorry in order to avoid any potential for "temporary" ground loops or momentary noises.  On the next rebuild, I'll try to take some pictures of the "process" in order to make it all a bit clearer.

     You mentioned a "braid", but this particular wire uses a foil shield for 100% coverage.  Braid is a bit less complete in coverage (and a LOT harder to work with)!

     In doing one of these rebuilds, the most time-consuming part is cleaning up the metal parts, but properly terminating the shielded wires is the *second* most time-consuming part of the job.  Still, I DO think it's worth it.

Sincerely,

Bill

P.S. Don't make a "special" effort to locate those spare parts, but I can *always* use additional parts.  If you happen to run into them, let me know.

Bill

[avahifi]

Bill, I have referred a couple of people who have e-mailed me for hard to find old Dyna parts to you.

I have used up all decent replacements years ago and feel bad that I no longer have any inventory of some of the pots and switches, etc.

Is it ok if I refer them to you?  I know you won't have everything, but there is always a chance.

Regards,

Frank