[avahifi]

The topology is essentially unchanged from the original.  The secrets are the amazingly good sounding parts we use.   

Seriously, the first sentence above is true.  The major differences between our original Super 70 rebuild (which fixed the time constant ratios as described by Bill Thomas a page earlier herein) and the Ultimate 70 is the application of a much more thorough understanding of power supply requirements and then with that issue drastically improved, being able to recalibrate all the pole points even more optimally.

It will be interesting to see if anyone can come up with an explanation as to what is really happening here with the power supply.

Thanks so much Bill for your awesome report.

Would you mind if we used your basic build comments and photos as a supplement to our U70 kit manual?

Best regards,

Frank Van Alstine

[Bill Thomas]

Dear Anand,

     Thank you for your VERY kind comments.  I'm glad you have enjoyed this LONG saga.  It has been a VERY interesting journey, with an EXTREMELY good sounding final result.  I hope the visual aspect of the build does justice to the OUTSTANDING sonic rewards this kit provides.

Dear Frank,

     I hope the final outcome was worth the LONG gestation period.  As you know, the many delays had NOTHING to do with the "Ultimate 70" kit.  *It* was basically completed during the first few days of the project, but I truly wanted the entire project to live up to the EXTREMELY high standards you set in the quality of the "Ultimate 70."  It would be my pleasure and a true HONOR if you decide to use any information contained in the "Rebuild Chronicles" for an addendum to the manual.  I am DEEPLY touched by your request.  You have my sincere thanks and admiration for a truly OUTSTANDING product, as well as your generosity to the audio community in general for so many years.  Thank YOU so VERY much!

Sincerely,

Bill Thomas

[joeriz]

Bill,

I just wanted to join the others and say 'job wonderfully done'.  Another first-class build all the way.  Thanks for the fun!

Joe

[rlee8394]

Bill,

Frank resolves THIS problem by increasing the coupling capacitor size to a total of 6.6 uF of high-quality film capacitors!

Did Frank change the coupling caps from parallel 2.2uF units to 3.3uF units. When I built my two U70's the spec was for parallel 2.2uF/400v film capacitors. From your photos, the brand of caps seem to be EPCOS, possibly B32674D4335K units?

Thanks,
Ron

[avahifi]

No change in these capacitors, they are paralled 2.2uF (4.4 uF total, not 6.6uF total).

Regards,

Frank

[Bill Thomas]

     Oops!  Another "senior moment" on *my* part.  I truly apologize for the error.  (I was working from my faulty memory, rather than actually taking another LOOK at the finished product.)  PLEASE excuse my mistake!  But either way, there shouldn't be any problem with the bass ZINGING right through the amplification chain!

Sincerely,

Bill Thomas

[rlee8394]

No change in these capacitors, they are paralled 2.2uF (4.4 uF total, not 6.6uF total).

Thanks Frank, just checking.
Ron

[Bill Thomas]

Dear Frank and Ron,

     Again, my apologies for the "goof" regarding the capacitor values.  I have corrected the article and made an appointment to be checked for "Early Onset Alzheimers."  (Come to think of it, it just *might* not be "early.")  Please forgive my mistake.  I guess it just proves that we're all human.

Sincerely,

Bill Thomas

[avahifi]

Don't feel bad at all Bill, the overall project looks out of this world good.

You should see some of the rebuild kits we get back for repair because the builder could never get them to work at all.

In some, the wiring work looks like somebody spilled a plate of spaghetti into the works.   

Best regards,

Frank

[Bill Thomas]

Dear Frank,

     I consider that HIGH praise.  You are certainly kinder than I deserve.  That said, I DO understand what you're talking about.  I remember building my first ever kit when I was nine.  It was an Eico 950B Resistance/Capacitance bridge.  The soldering "tool" I used was a Wen 250 Watt gun!  The truly AMAZING thing is, it actually worked!  (And it worked perfectly for MANY years until it was lost in a family move.)  Not exactly a "Lab Grade" piece of test equipment, but it was good enough at the time.

     When I started acquiring a LOT of Dynaco gear, my original goal was to just put together a nice "Vintage System" of a Stereo 70, a PAS-3X, and FM-3 tuner and some sort of Dual turntable - *just* in case I ever needed to play a "record."  (Remember those?)  This a step "up" from the system I had as a teenager.  (I had an SCA-35, rather than the Stereo 70/PAS-3 combo.)  I didn't need anything "fancy", I just wanted something that looked good.  Well... after buying over 20 Stereo 70s and who knows HOW many preamps and tuners, the BEST Stereo 70 was "The 38 Year-Old Virgin", and it *still* had a couple of pits in the plating.  The BEST PAS preamp turned into the "Last of the Dinosaurs."  I DO have a really nice FM-3, but it took buying over 25 of them to find a nice one.

     Most of the units that had been assembled by well-intentioned kit builders had the appearance of a nest of Tarantulas, with solder joints that resembled the appearance of poorly cleaved granite.  One of my "favorites" was the "upgraded Driver Board from the amplifier that turned into our "Ultimate 70."  (Boy, was THAT visually "interesting!")

     I'm a "meat and potatoes" kind of guy.  While I DO like pretty things, I believe that the CORE of the unit should be built for the long-haul.  I don't like stuff that has to be constantly "fiddled with" just to keep it functioning normally.  (That *could be because I used to be a "Corvair Guy.")  A Ferrari may look pretty, but my 1997 Dodge Grand Caravan has over 265,000 miles on it and starts EVERY time.  It also passes emissions inspection EVERY time as well.  It has had one complete valve job.  That's it!  (Synthetic oil!)  I can haul a LOT more Dynaco gear from storage in IT than I EVER could transport in a Ferrari!  (But if you happen to be giving away an XK120 anytime soon, I'll be GLAD to "suffer" with it to take it off your hands! (lol))

     I'm a bit delayed in the "Final Update (covering the tube cage/cover and final assembly).  My MUCH "better half" just had a total knee replacement yesterday, so I'm doing some much-needed "time investment" with her.  I'll be "back on the horse" shortly and we'll finish up the cosmetics soon.  In the meantime, I'm sure enjoying the fruits of our four-month project when I DO get time at home.  In the final report, I'll pass on my "observations" about how the amp sounds loaded with NOS Mullard EL34's!  In fact, one of the things that REALLY surprised me about the "Ultimate 70" was just how really GOOD it sounded with those lowly Electro-Harmonix EL34EH's.  I can't wait to "stuff it full of the GOOD stuff!"

     More to come as soon as I can get to it!

Sincerely,

Bill Thomas

[Brett Buck]

January 25th, 2009 - Update Three:  "It Sounds Like a Stereo 70 - Only Better!"

     Before we get to the discussion of "sound quality", I wanted to report on the initial "turn-on" of the "Ultimate Stereo 70" amplifier.

     I completed the wiring of the amplifier around 2:00 AM Thursday morning.  I simply couldn't wait, so...  I stuffed it with the supplied 6GH8A driver tubes, a NOS Mullard GZ34/5AR4 and added a new factory-matched quad of Electro-Harmonix EL34EH Output tubes.  (These are the tubes I use to "test" new amplifier projects.  In case something goes *drastically* wrong, I'm not out a bunch of bucks.)  I plugged the amplifier into my trusty Variac and slowly brought up the Voltage.  No signs of stress or strain, everything powered up nicely.  But there was no sound!  With a stock Stereo 70, when you put your ear next to the speaker, you can *usually* hear SOME trace of "thermionic emission."  And when you power up a stock Stereo 70 without the bottom cover installed, there is almost always *some* trace of hum.  Not THIS time.  Total silence!

   That's funny, the exact same thing struck me when I first turned on my (well, my Dad's that I had rebuilt and returned to him) U70. Hooked everything up, cringed as I hit the switch (for fear of releasing the magic smoke that makes it work), and, *nothing*. Oh, geeze, I must have really missed something, didn't even hook the power up right. But no, I heard the faint "tinking" of the tubes heating up. So, at least the heater supplies work, but there must be a short or open in the signal path. Fired up a CD, and boom, everything works like it should have, but *no* noise.

  

  Not quite believing that things should be this quiet, I fired up a little portable CD player I had plugged into those nice, new, gold RCA Input Jacks.  And - there it was!  GORGEOUS music from a dead silent background!  Even those "less than perfect" Electro-Harmonix EL34EH's couldn't disguise the fact that something truly SPECIAL was going on!

     I think you will be somewhat surprised how small the improvement with  "better" tubes will be. I used Electro-Harmonix 6CA7s just to start with, in case I did something stupid. Sounded great, but I was sure that original Mullards would be "better". I borrowed a set from a friend, all tested pretty high and matched, but the overall improvement was negligible if at all. In fact, it seems very slightly more "neutral" with the 6CA7s, and a little warm with the Mullards. It may be different in the ear of the "behearer" but it was certainly not a significant difference. It was even less clear when switching to RCA and other tube brands.  I went back to the EH 6ca7s and am not lusting for Mullards any more, at least for this application.

    I would also add that after the thing having run about 8-hours a day for about a year, only one problem - an arcing Sovtek rectifier tube. Everything else has been completely bulletproof.

      Brett

[Bill Thomas]

    I would also add that after the thing having run about 8-hours a day for about a year, only one problem - an arcing Sovtek rectifier tube. Everything else has been completely bulletproof.

     This is the exact reason I simply will NOT use any Chinese or Russian GZ34/5AR4's in ANY of my Stereo 70's.  I have a good supply of NOS Mullard GZ34/5AR4's and have never had one fail in ANY Stereo 70.  I'm not suggesting that a Mullard will NEVER fail, (I did have ONE failure out of several dozen I have sold - which I promptly replaced), but in general, Mullard GZ34/5AR4's are simply MUCH more robust and long-lasting than any of the current-production rectifiers.

     I hear and read reports that "The Chinese tubes are getting better and better these days."  Perhaps so, but my personal experience does not bear that out.  They appear to still have a long way to go before they will be as reliable as a NOS Mullard.

     I hope to report on the difference in sound quality with Mullard EL34's when I get around to our final "update".  If the difference is truly "negligible" then the "Ultimate 70" kit becomes even more "valuable".  Unfortunately, other "outside pressures" are taking my time for the next week or so.  (Family ALWAYS comes first!)

Sincerely,

Bill Thomas

[Brett Buck]

    I would also add that after the thing having run about 8-hours a day for about a year, only one problem - an arcing Sovtek rectifier tube. Everything else has been completely bulletproof.

     This is the exact reason I simply will NOT use any Chinese or Russian GZ34/5AR4's in ANY of my Stereo 70's.  I have a good supply of NOS Mullard GZ34/5AR4's and have never had one fail in ANY Stereo 70.  I'm not suggesting that a Mullard will NEVER fail, (I did have ONE failure out of several dozen I have sold - which I promptly replaced), but in general, Mullard GZ34/5AR4's are simply MUCH more robust and long-lasting than any of the current-production rectifiers.

That has been my (limited) experience, too. I have had several of them go belly-up after a few months in other cases, and have scrounged for older tubes to use. I don't have any Mullards but older RCAs, etc, seem to be far more reliable than the cheap currently-available version.  It's definitely the weak point. The Sovtek was replaced in the U70 with an RCA tube from the pre-rebuild amp, from about '69-'70.

     I hope to report on the difference in sound quality with Mullard EL34's when I get around to our final "update".  If the difference is truly "negligible" then the "Ultimate 70" kit becomes even more "valuable".  Unfortunately, other "outside pressures" are taking my time for the next week or so.  (Family ALWAYS comes first!)

    It will be interesting to hear your insights.

   Fantastic project, nicely executed!

    Brett

[avahifi]

Hi  Bill,

Have you had the opportunity to try any "tube rolling" with your Ultimate 70 amplifier kit yet?  I will be very interested in finding out what you hear and recommend.

With my latest "fun episode" in playing with a new Super Pas Three rebuild here, (adding Insight line buffers and being very happy with the results) think about your Super Pas Three rebuild kit again.  When it is done, send it back for the Insight buffers and then you will have a tube amp and preamp combination that will be hard to beat at ten times the price.

Best regards,

Frank Van Alstine

[Bill Thomas]

Hi, Frank!

     Sadly, I have been totally yanked away from the electronics projects for the past four weeks.  My MUCH better half just underwent total knee replacement surgery and I have had to attend to "patient support mode" for awhile.  But, I'm comin' back with a vengeance!  I should be back in the saddle again within the next week or so.  We'll add the final installment to the "Ultimate Stereo 70" build, we'll finish our second version of the FM-3 tuner and we'll begin a brand new project as well.  We'll also be taking a side trip into the world of "roll yer own" printed circuit boards - it's NOT as hard as some folks might think!

     Hang in there, Friends!  LOTS of good stuff ahead!

Sincerely,

Bill

[Flyquail56]

Hey Bill!

Please give Mrs. Thomas our best wishes for a complete recovery. A lot of us are a little too old now for the 100 meter hurdles (at least I certainly am), but I hope she's better than new very soon 

You are to be commended for being a servant leader!

Best,
Mike

[avahifi]

Yes indeed, best wishes for a good recovery for your wife, Bill.  I had my right hip joint replaced a couple years ago and that went very well but I still can't do high hurdles very well.

However it does give me a nice rest break at airport check in lines when their buzzers go off and I get whisked aside by a couple of pro football linebacker types to be strip searched in spite of my "get out of jail free" card from my doctor.

Best regards,

Frank Van Alstine

[avahifi]

Just in case you missed my post in the AVA circle, I am posted the recent very easy FREE upgrade to the U70 here too:

FREE ULTIMATE 70 AMPLIFIER UPGRADE

If you have an Ultimate 70, here is all you need to do:
1.    Make sure the amp is cold and unplugged.
2.    Locate the six wires connected to the PC board at the hole in the chassis where the quad filter cap once was located.
3.    Disconnect the two red transformer leads from the eyelets marked RED.
4.    Disconnect the wire from the eyelet marked B+.
5.    Connect the B+ wire to either of the eyelets marked RED.
6.    Connect the two red transformer leads to the eyelet marked B+ (two wires need to go into one hole together).
7.    Readjust bias.
8.    Listen again.

This makes a major sonic improvement by connecting the power to the audio board regulated power supplies after the choke instead of before the choke.

Simple and very effective.

Regards,
Frank Van Alstine

[Bill Thomas]

Dear Frank,

     I hope you will forgive me for my delay in responding to you.  I have been a bit preoccupied with prototyping replacement circuit boards for the FM-3 tuners, so I've been going through several YEARS worth of "the midnight oil" over the past two weeks.

     This is a truly OUTSTANDING modification to the Ultimate 70!  I think it is pretty special when a small modification can be made (which costs NOTHING) that can improve the final audio results so much!  It also says a LOT about just how much this "sickness" we call "audio excellence" consumes us.  (You don't get too much sleep either, do you? (lol))

     My life has been in some turmoil for the past few months, but things are *beginning* to settle down a bit.  Once I am able to put this particular FM-3 up "on the bench" for final "burn-in", I'll be able to get back to the REST of my "loose ends" (like spending that quality time enjoying the Ultimate 70 WITH the new "mod" and a set of matched Mullards.  I'm only about a MONTH behind on THAT particular set of events.)  Sorry for the delays.

     By the way, the surgeon's last check-up of the new knee left him ecstatic over her progress!  He released her from further Physical Therapy chores and told her to check back in six months!  It's still tough for her to get down a flight of stairs, but in almost every other respect, her NEW knee is performing like an Ultimate 70 WITH the new "mod." (lol)

     To all who expressed their good wishes, I can only say a VERY humble "Thank You."  And to any who might deny the existence of God, all *I* can say is, "Oh, YEAH?  I have PROOF otherwise!"  *Hopefully*, He will help guide ME through this particular tuner problem.  It's funny how these things happen.  If I had not discovered the problems with using silver-bearing solder mixed with the existing solder, I might never have been "guided" into making new PC boards for the FM-3.  ("Guided" is a euphemism for "forced.")

     I guess this brings me to the final, inescapable cautionary warning:  PLEASE, folks - no matter how much you *think* silver-bearing solder will "improve"  your old electronic equipment, RESIST the temptation to "improve" your equipment this way.  Here is a beautiful Dynaco FM-3 tuner that contains only THREE bad parts - PC-7, PC-8 and PC-12!  While it operated quite well for a long time, over time, the non-homogeneous mix of silver and regular solder apparently had problems due to the heating and cooling cycles inherent in an FM-3.  Silver-bearing solder requires a LOT more heat for a good, non-crystallized joint.  Mixed with regular tin/lead solder, the results are unpredictable over time.  Save the silver-solder for bonding ground straps and radials at AM radio stations.  THAT is what it is truly good for!  (And by the time you solder 180 ground radials to the copper ring at the base of the tower, and the 4" ground strap that comprises the station's main ground connection, you will PINE for tin-lead solder connections!)

     I should also mention that the new "lead-free" solders are NOT a good idea either.  They have been thoroughly examined by the Military and have been found "not suitable" for long-term "survival" of equipment.  The Military won't TOUCH them now.  I recommend that YOU don't either.  Besides, we "Old-Timers" grew up using lead-based solders and WE turned out...  Never mind!

Sincerely,

Bill Thomas

[audiojerry]

I want to thank JerryM for directed readers to this thread from here: http://www.audiocircle.com/index.php?topic=74577.0.

And I also wish to extend a belated thank you to Bill for his generousity for writing this immensely helpful and inspiring narrative. It has certainly piqued my interest in trying to perform a mod myself.