Just Joined, Building a Dyna ST-35

Hi. I am Dan from Fort Worth. I recently built Steve Deckert's ZEN Triode (picture below), and now I am building an ST-35.

In my youth, my first good stereo was based on an SCA-35, which I built from the Dynakit.

Any way, I am going to read everthing here and get started on my build. I will do my own chassis, and point-to-point wiring, BTW.

Expect many questions, and thanks for being here.

Danner

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Thanks for that.

My first order of business is output transformers. I need 8 ohm, and don't care about the other tap(s). The transformers I have found so far are from Triode Electronics, which are claimed to be made to Hafler's specification, excepting the 4-ohm tap. They look OK, I guess. I was wondering if Edcor could make some for me? Or, is there something truly unique in the OEM transformers?

I will take a look at Dynakitparts, who I have no knowledge of.

Danner wrote:Thanks for that.

My first order of business is output transformers. I need 8 ohm, and don't care about the other tap(s). The transformers I have found so far are from Triode Electronics, which are claimed to be made to Hafler's specification, excepting the 4-ohm tap. They look OK, I guess. I was wondering if Edcor could make some for me? Or, is there something truly unique in the OEM transformers?

I will take a look at Dynakitparts, who I have no knowledge of.

About three years ago, I also built a Dynakitparts ST-35, except for the (Triode) transformers which I already had on hand. I fully agree with Peter Capo's comments and I too am extremely pleased with this amplifier! I would seriously consider the Dynakitparts or Triode reproduction transformers. I think you will be very pleased. Just FYI, Kevin at Dynakitparts is very courteous and always goes out of his way to please his customers. All of his products are truly top-notch and all of the parts including chassis and covers are fully interchangeable with the originals.

Best Regards,
Charlie

Last night I went all through the dynakitparts.com website. Wow! It's like Dynaco is still in business

Thank you, this is going to be much easier than I expected.

Edcor does make a suitable transformer, the CXPP25-MS-8K/23%. I have a pair that I had ordered for a ST-35 because it has a 16 Ohm output for my JBL 2420 16 Ohm compression drivers. The problem is that they are somewhat larger than the Z565. I tried them on a standard ST-35 chassis and thought the layout was much too crammed together. I could have made it work,however.

I, instead, purchased a pair of Z565's from Triode. (And a Diytube chassis and board for the Edcors, not yet finished.) The Z-565 transformered ST-35 has been running for about 2 months and sounds amazing. Much better than any of my SS power amps, of which I have a few.

The only real change that I made, from stock, was a set of Mundorf silver-in-Oil coupling capacitors which had to be mounted under the standard ST-35 chassis. (They just barely fit). The amp sounded a little bright and somewhat harsh until everything settled in. Never has any single component improved my hi-fi- setup as much.

You've made a good choice in the ST-35 Dynaclone

Stevedel

The diytube site is another with lot's of info under the ST-35. The EFB mod by Dave Gillespie is well worth it for output tube life and sonics. It can be added to either the diytube board, SCA-35 or ST-35.

It will work better than the adjustable cathode bias std on one of the boards and an optional add on on the other. Many have tried it in the last 2 yrs. and go to post #5 here to download his paper on it.

http://www.diytube.com/phpBB2/viewtopic.php?t=4374&sid=cd2d759434dfb8bb8480ae6bea354317

Besides improved sonics it allows any EL84 tube to be used without danger of shortening it's life. You can set the dissipation to a safe level lower than 12 watts. Back in the day they ran the tubes hot as they were cheap and max power with the low cost cathode bias was the order of the day to keep the price of the amp low. Also today the line voltage is usually too high.

Another improvement is to add a good choke and there are affordable ones from Gregg @ Classic Valve Design & Edcor. They can replace the 50 ohm resistor in the PS.

If you haven't ordered Output Trans, another well recommended Z-565 clone is from Mike @ Magnequest , and he has them in Nickel Lams also. He does runs every so often. They have the stock 8 & 16 ohm output impedance of the originals and the second hand set I found are beautifully done.

Hope that helps!

Randy

Full agreement with the above post. The EFB was incorporated in my build and it works great. Be sure all the output tubes are carefully matched if using the "simple" version of the mod. I used Magnequest OPT's as well since I needed the 16 ohm tap.

I'll 3rd adding Dave Gillespie's EFB to your ST-35. It's inexpensive, easy to do, and took the SCA-35 (same output circuit as the ST-35) from a dull amp I never used, to a very listenable amp. Output tube life is extended, the amp puts out more power, and sounds far better. What's not to love?

Here's a link to EFB (Enhanced Fixed Bias) implementation in a ST-35, as well as a general description of why it works and how to do it: Dave's Lab

Edit: A copy / paste link for those not logged in...

http://www.tronola.com/html/dave_s_lab.html