[Bill Thomas]

     Allow me to introduce you to our second Dynaco Stereo 70 re-build - "Don't Call Me 'Dimples'!"  (This is the classic "Open Cover" shot!)  As shown, this amplifier is equipped with a NOS Mullard-manufactured, GE-branded GZ34/5AR4 rectifier, two NOS Sylvania 7199 driver tubes and a factory-matched quad of NEW Electro-Harmonix EL34EH Output tubes.  This is the configuration I used to "burn-in" the completed amplifier.

     This amplifier is very similar to our first re-build called "Nothin' Fancy", but differs in a few respects.  First, this re-build used ceramic tube sockets, rather than "Micanol" sockets for even MORE reliability over the stock plastic tube sockets.  Here is a picture taken with the octal tubes removed.



  The Driver Board features Illinois Capacitor MWR series 1.0 uF capacitors to couple to the Output tubes for a bit MORE improvement in the bass response.  Here is a picture:



     Note that every 1/2 Watt carbon-composition resistor on the Driver Board has been replaced with NOS Allen-Bradley carbon-composition resistors that were carefully matched to better than 0.1%!  As with "Nothin' Fancy", the 1 Watt resistors were checked and found to be very close in value so they were not replaced (except for the 1,000 Ohm resistors in the feedback circuit - they WERE replaced.)  The 82 pF and 390 pF capacitors were also in fine shape, so they were retained as well.  Here is a picture of the original Driver Board:



     And here is a picture of the completely rebuilt and restored Driver Board prior to installation:



     Quite a difference, wouldn't you say?  All traces of contamination have been removed and the new parts really make it visually "pop!"

     Now, on to the "meat" of the project.  Here is a picture of the under-chassis wiring:



     If you followed our first rebuild, "Nothin' Fancy", you will notice that they are quite similar.  (Here's a picture of the under-chassis wiring on "Nothin' Fancy" for comparison purposes):



     Again, the wiring is based upon Dynaco's original "factory-wired" scheme.  Eagle-eyed viewers will notice that the left-most resistor on the bias supply terminal strip has been  changed in value from "Nothin' Fancy."  "Don't Call Me 'Dimples'!" uses an 8.2K resistor in this location, while "Nothin' Fancy" used a 4.7K resistor.  ("Nothin' Fancy's" 4.7K resistor has now been changed to the same value - 8.2K)  This change was made to accommodate a broader selection of EL34 Output tubes.  It was discovered that *some* current-production tubes require a *bit* more  negative Voltage in order to properly set the "idling current" so the value of the resistor was changed.  (We live and learn, don't we?)

     Here is a picture of the back of the amplifier. 



     Notice the slight "dimple" around the fuse holder (Thus, giving "Don't Call Me 'Dimples'!" its name!)  The amplifier was seriously damaged in transit when I purchased it due to insufficient packaging.  The fuse holder was "punched-in" so far that the top of the fuse holder cap was flush with the rear edge of the bottom cover!  The Left Channel speaker Output terminal board was broken.  It took a LOT of straightening to return the back panel of the amplifier to a reasonably "flat" configuration.  While there is still a "dimple" around the fuse holder, it is only a "slight" distortion to the metalwork.  Any further straightening would have caused a LOT of damage to the rear panel's plated surface, so we opted to "quit while we were ahead."  I think it was a "reasonable trade-off.  Don't you?

     Finally, here is a picture of the completely assembled amplifier with the tube cage/cover installed:



     Note that this amplifier was originally produced around 1962 or 1963 (according to the transformer date codes) as a kit.  The tube cage/cover has a slightly "coarser" hole pattern than later amplifiers from the 1970's and is equipped with a foil labeled logo that reads "Dynakit" rather than a plastic sticker that reads "Dynaco."  Yes, it has the more desirable cloth-covered wires on the transformers.

     How does it sound?  Simply WONDERFUL.  It actually has just a *tiny bit* more "definition" in the bass region.  I would chalk that up to the 1.0 uF coupling capacitors.  Of course, it has that "Magic Middle" that Stereo 70's are FAMOUS for.  The top end is smooth and not the least bit "constricted."  This is one truly "musical" amplifier.

     While I offered "Nothin' Fancy" either fully tubed, or as a bare amplifier (YOU supplied the tubes), I would prefer to sell "Don't Call Me "Dimples'!" with a MINIMUM configuration as shown in the first picture.  It is CRUCIAL to use a high-quality rectifier tube in a Stereo 70 due to the high Voltages involved.  Chinese rectifiers are NOTORIOUS for arcing over, even in normal operation.  Russian rectifiers are a *little* better, but NOTHING compares to the sturdiness of a NOS Mullard.  Since a serious arc-over can kill the quad cap and destroy the Power Transformer in short order, I must STRONGLY recommend the use of a Mullard-manufactured rectifier.  When the Stereo 70 was FIRST introduced, it was equipped with Sylvania 7199's as Driver Tubes.  This was a direct result of comparing every known 7199 that was available back "in the day."  The Sylvania was simply the quietest tube available.  Later versions of the Stereo 70 were equipped with RCA 7199's and I will be happy to let you choose which NOS 7199 tubes you desire.  PLEASE don't even CONSIDER using Sovtek 7199's.  They really weren't very good when new, and there is really no reason to "pinch pennies" and use them now.  The Electro-Harmonix EL34EH Output tubes were factory-matched and are a "good (but not BEST)" Output tube.

     Now, here is the pricing:

As shown, with all pictured tubes included:          $550.00 (due mainly to the ceramic tube sockets)

As shown, but with NOS Mullard-manufactured matched EL34 Output Tubes:  $850.00

As shown with only the NOS Mullard/GE GZ34/5AR4 (YOU supply the 7199's and EL34's):  $500.00.

     I REALLY can't stress enough the importance of the rectifier tube!  IF you can somehow convince me that you have a suitable NOS unused rectifier, and will sign a release form stating that any damage to the amplifier caused by a bad rectifier YOU supply will NOT be covered by my guarantee, I will allow the bare amplifier to be sold for $400.00.  I can ASSURE you this WON'T be an easy job "convincing me."

     I will guarantee the amplifier (except tubes and transformers) for a period of one year from the date of purchase.  This covers all new parts and workmanship.  Tubes are guaranteed for 90 days.  The guarantee is voided if tubes have OBVIOUSLY been abused.

     This turned out to be a really BEAUTIFUL amplifier.  The ceramic tube sockets will ELIMINATE any worries about "socket deformation" for decades to come.  The sound stage is wide and detailed, and the music appears from a black background; all the things you WANT an amplifier to do well.  Contact me at nostubesforyourdynaco@gmail.com for more details, or to purchase the unit.  If you would like to find out more about the rebuild, I have detailed the build at: http://www.audiocircle.com/index.php?topic=58731.0

     We'll give Stereo 70's a rest for now.  Our NEXT rebuild will be a Dynaco PAS-3X preamplifier - complete with those "special" tone controls in NOS condition (I just happen to have ONE set that has NEVER seen a soldering iron!  It will soon!)  It should be interesting so:

     Stay Tuned!

Sincerely,

Bill Thomas

[cryoparts]

Bill,

I've been really enjoying the "diary" you have kept on the rebuilding of the last two ST-70's, keep it up!

Peace,

Lee

[Bill Thomas]

Dear Lee,

     Thanks for the feedback.  Sometimes I wonder if anyone really wants to see this stuff.  But there are SO many of these amplifiers still around and they really ARE better than their cost would lead one to believe, that I simply HAD to let people know that restoring them is within the capability of almost ANYONE here.  These articles show some of the problems, and how to resolve them and the pictures can help potential "restorers" avoid excessive hum and noise.

     I'm really hoping that this is a SERVICE, not a dis-service! (lol)

Sincerely,

Bill Thomas

[jon_010101]

Great work! 

[cryoparts]

Dear Lee,

     Thanks for the feedback.  Sometimes I wonder if anyone really wants to see this stuff.  But there are SO many of these amplifiers still around and they really ARE better than their cost would lead one to believe, that I simply HAD to let people know that restoring them is within the capability of almost ANYONE here.  These articles show some of the problems, and how to resolve them and the pictures can help potential "restorers" avoid excessive hum and noise.

     I'm really hoping that this is a SERVICE, not a dis-service! (lol)

Sincerely,

Bill Thomas

I, for one, enjoy the updates and look forward to more.   

Lee

[richidoo]

The before and after driver board pics are COOL!    I love the look of those old black caps, but probably not the way they sound!

I had to do a double take on the prices, at first I thought it was just tubes, or maybe just the service fee to build a customers amp. Man there is a lot of brand new crap out there for $850 - what a bargain for a classic tube amp in new condition and with a warrantee???! This is obviously a labor of love for you, truly beautiful work. Congrats!!
Rich

[Bob01605]

Bill,

   Nice job on the rebuild - another amp saved from the scrap heap created by a few misguided souls who specialize in "parting out" old Dynaco amps.

I do have to take issue with Rich's comment about "Man there is a lot of brand new crap out there for $850" - Some of the new amps presently being offered as kit and wired units are most definitely not "crap". The power transformers available from Triode and Dynakitparts run much cooler, quieter and have much greater power transfer capabilities. I have to also wince every time I hear about the wonders of the "cloth lead output transformers" that Dynaco made. Those ouput transformers were good - no doubt about it  - BUT - those output transformers have been reverse engineered and now Triode and Dynakitparts sell output transformers that, not only IMHO but in the opinion others who have done blind listening tests with me, sound every bit as good as the original transformers.

I suggest to Rich that he not paint all newer versions of the Dynaco ST-70 with such a broad brush and make implications that these newer amps are ALL "crap".

Bob Latino

[cryoparts]

We'll give Stereo 70's a rest for now.  Our NEXT rebuild will be a Dynaco PAS-3X preamplifier - complete with those "special" tone controls in NOS condition (I just happen to have ONE set that has NEVER seen a soldering iron!  It will soon!) 

Sweet...

Lee

[Bill Thomas]

     Thank you all for the positive (and most kind) comments.  I certainly DO enjoy doing these "projects, Lee."  Rich, this IS a labor of love.  I've been a Dyna-Fan since the early 60's.  Bob, I consider that VERY high praise.  Your work is certainly impeccable and I am a BIG fan of your "projects" as well.  As you might guess, I have seen these amplifiers turn into some pretty *strange* creatures before they wound up in my storage units.  Most of them have been "improved" by well-intentioned "tinkerers" until they either didn't work anymore, or have been turned into something that is either unreliable, or even dangerous!  I have kept "improvements" to a minimum because I wanted folks to have a chance to see the real "genius" of Dynaco's engineers (not MINE, THAT'S for sure! (lol)) in being able to produce an amplifier of real audio "quality" at an astronomically low price-point.  The only real changes I have made have to do with the size of the Output coupling capacitors.  When these units were originally produced, a 1.0 uF capacitor was the size of a "C" cell battery and cost more than an EL34, so they "skimped" on the size.  The changes to the bias supply are simply to enhance the reliability factor.  Nobody *I* know would even consider using a selenium rectifier in this day and age.  (Yes, I actually DO have a few NOS selenium rectifiers in my NOS "parts stash" but they will remain there unless someone INSISTS on getting one.  I can assure everyone that this would NOT be a good idea!)

     By the way, if you're an "Eagle-eyed" viewer of the pictures, you *might* notice that I used a D.P.D.T. slide switch for the Stereo/Mono switch, but left one side unwired.  This was actually VERY intentional.  I have done this so people can add a proper bandpass filter to the input while still maintaining the ability to switch the input to Mono operation, yet still accept an input signal from both input jacks.  I leave it to future "tinkerers" to add the filter.

     I will be getting into an interesting Stereo 70 build later.  It will NOT be a "stock" Stereo 70 by ANY means.  But it WILL feature "state of the art performance" with a new Driver Board that simply has to be seen to be believed!  That's all I'm saying for now.  Yes, there will be more (relatively) stock Stereo 70's to come as well.  And just wait until we start tackling an FM-3 Tuner rebuild later in the year!  Right now, we're waiting for some parts for our current PAS-3X project, but I will have an update coming up VERY soon.

     Just remember, ALL of these "projects" are available for purchase at "reasonable" prices.  (If you can tell me where someone can actually BUY an equivalent Stereo 70 equipped with NOS matched Mullard EL34's for under a thousand Dollars, I'll EAT it!)

     By the way, I received a report yesterday from our purchaser of "Nothin' Fancy."  He purchased the amplifier and a pair of 7199's only, because he had both GZ34/5AR4 rectifiers and EL34's available.  As it turned out, his rectifiers were old and fairly used up.  Also, they were the Japanese-manufactured versions.  Needless to say, after three of his used-up rectifiers arced over, I supplied him with a NOS GE USA-manufactured NOS 5AR4.  (I would consider it the "second-best choice" in NOS rectifiers for these amplifiers.)  No arc-overs, no added drama.  Everything looks and sounds SUPERB!  (Yeah, I was kinda "sweatin' bullets" on THAT one myself! (lol))  NOW you understand why I so STRENUOUSLY recommend using a NOS Mullard rectifier for these amplifiers.  PLEASE don't even CONSIDER using a Chinese GZ34/5AR4 in a Stereo 70.  It certainly won't survive very long.  But it could also destroy the quad capacitor AND blow the Power Transformer due to arc-overs.  MANY of these Chinese "so-called" GZ34/5AR4's are really re-branded 5Y3's.  (Want one?  I have several "Westinghouse" branded tubes that actually have a faint "5Y3" printed on top of the tube!)  Needless to say, a 5Y3 can't even come CLOSE to handling the Voltages AND the current drain of a Stereo 70.  PLEASE don't even try them!

     That's all for now.  Comments (and opposing viewpoints) are welcome.  MUCH more to come!  Stay tuned!

Sincerely,

Bill Thomas

[Bill Thomas]

     OK folks!  In order to "keep the stories coming", "Don't Call Me 'Dimples'!"  NEEDS to find a new home.  (I'm using the proceeds from each amplifier to fund the next "project).  So, to make it even easier for SOMEONE to enjoy that wonderful "Tube Goodness" a Stereo 70 can offer, I've decided to offer a "Labor Day Sale" price reduction of $50.00 on each configuration of the amplifier.  I have changed the original ad to reflect the changes in pricing.  This sale price will only last until 11:59 PM EDT on September 1st.  After that, it's back to the original price.

     You won't find a cheaper price ANYWHERE for a completely restored Stereo 70!  And the ceramic sockets mean THIS amplifier would be an IDEAL foundation for someone who wants to "hotrod" a Stereo 70 with a replacement Driver Board.  By the way, the ceramic sockets I used are NOT current-production sockets.  These are ex-US Military sockets, and THAT means they have the cast-in "wiggle room" for the locating keyway.  I'm not saying you *can't* break off a keyway, but it's a LOT harder than with the current-production versions.  (And the contacts grip the tube pins like the "Governator's!" handshake!)

     Remember, this is a VERY limited-time offer.  The price goes back up on Tuesday morning.

Sincerely,

Bill Thomas

[Rocket]

Hi Bill,

Wonderful work and great post.  Yes we are interested in your posts regarding your restoration projects.

Btw at some point in time could one of these amps be configured for 240V.

Best wishes

Rod

[Bill Thomas]

Dear Rod,

     Thanks for the kind words.  In order to produce a unit that will work on 240 Volts, the Power Transformer would have to be replaced.  The current US Price on a 240 Volt Primary Power Transformer is $159.95 (plus shipping from Chicago, Illinois).  That would turn a $400.00 amplifier into a $600.00 amplifier.  I would need a firm order (with a $200.00 deposit) in order to put one together.  (I would also want to find a source for a suitable Power Cord with the proper plug for your location - I would think Jaycar would have them.)  Other than that, it's a (relatively) trivial matter.

     I Hope this is useful information for you.  Again, thanks for the positive comments.

Sincerely,

Bill Thomas
     

[Bill Thomas]

     Yes, in just a few hours, your chance to get a Classic Dynaco Stereo 70 will get $50.00 more expensive!  At 11:59 PM tonight, the price for "Don't Call Me 'Dimples'!" goes back up to its original price.  If you have been *thinking* of getting a Stereo 70 to play with, NOW is the time to "take the plunge."  Don't spend this much (and MORE) on a beat-up old unit from eBay.  I stand behind my work with a one year guarantee on new parts and workmanship, and I guarantee all tubes for 90 days as well.  (You won't find many folks on eBay who will do THAT!)

     Seriously, "Dimples" needs to GO, so I can move on the the next projects.  You won't find a better price on a restored Stereo 70 ANYWHERE.

     Just e-mail me at nostubesforyourdynaco@gmail.com and I'll do the rest.  I'll be counting down the minutes! (lol)

Sincerely,

Bill Thomas

P.S. I hope all the US residents had a WONDERFUL Labor Day today.  It's back to the salt mines tomorrow!

Bill

[Bill Thomas]

     "Don't Call Me 'Dimples'!" is still available.  She's a pretty sweet sounding amplifier - complete with original Dynaco transformers!  Precision-matching the resistors results in a VERY balanced sound between channels.  (And I'm running low on "project money"), so if you have ANY thoughts about finding a "good tube amplifier" to play with, this would be a GREAT choice.  Also an IDEAL foundation to do your own "mods" with upgraded Driver Boards, etc.  She deserves a good home!

Sincerely,

Bill Thomas

[Bill Thomas]

     It appears that "Dimples" is about to find a new home.  I want to thank everyone for the words of encouragement and the MANY who just "window shopped."  The sale of "Dimples" will allow me to get knee-deep into our next project VERY soon.  Our next project will be Frank Van Alstine's "Ultimate Stereo 70".  Since I have not had the opportunity to build one before, this will be new territory for me as well.  I will be documenting the build, just as I have with our previous builds.  I have heard SO many WONDERFUL things about Frank's take on the Stereo 70 that I feel like a kid in a (ear) candy store.  More details to come.

     Thanks again!

Sincerely,

Bill Thomas

[Gvt1911]

Bill, Now you are finally going to build a NICE st70 with Franks board !!  You won't believe your ears !! 
Best of Luck !

[Bill Thomas]

September 20, 2008 - Update:  "Dimples" is heading to her new home!

     I would like to thank everyone for their interest in "Don't Call Me 'Dimples'!"  She is now heading on a LONG voyage to a distant land.  (*I* should be so lucky!)  Our next *mostly* stock Stereo 70 is already spoken for as well.  But before that happens, we will be building a VERY special amplifier.  We'll be taking a badly modified Stereo 70 to new heights of functionality with Frank Van Alstine's "Ultimate Stereo 70"!  We will begin on Monday, September 22, 2008, with construction of the OUTSTANDING Driver Board.  We will also be installing Frank's upgraded Input and Output connectors.

     THIS project will be something truly WONDERFUL.  Meanwhile, stay tuned for our final report on "The Last of the Dinosaurs!"  One last (mostly) new PAS-3X preamplifier.  It is finally finished, tested and reproducing some very beautiful music, as we speak.  It will be available for purchase as well.  I will reveal our final surprises in the "Construction Chronicles" in the "Vintage Circle" on Sunday, September 21, 2008.  This is truly as close to a new PAS-3X as you are likely to get.  The modifications we have made can be applied to any existing PAS preamplifier for improved performance and increased functionality.  Watch for the Classified Listing, no later than Monday, September 22, 2008.

Sincerely,

Bill Thomas