ST 35 Finally Powered.

for the DIY ST35, the Dynakit and every other PP EL84

ST 35 Finally Powered.

Postby andrewbee » Sun Jan 19, 2014 11:29 am

Hi all,

long time lurker here with first post. Started out with KT88 PP then been using SE for maybe the last 10 years or so but have been contemplating a PP EL84 for awhile,(EL84 is great sounding, easy to drive and cheap - whats not to like!) as I have parts build it easily (could almost open a store with my parts collection over the last almost 30 years :)) but as I get older I grow more lazy so and was going to order a Dynaclone ST35 kit instead but changed my mind. Ordered a ST 35 board and parts from Triodeel in the middle of September last year, received it about 10 days later (Cayman Islands) and built it maybe 2 weeks later. Finally powered it up yesterday, its just been sitting on my bench while I have been busy with life.
I used Hammond 300 series Power and 8H choke, F&T filter caps, Hexfreds, Hovland for coupling and cloth lead Z 565's which I had to renew the leads on as the insulation left a lot to be desired after 50 years. JJ 12AX7 / 12AU7 and Sovtex EL84's.
So far so good, my PS voltages are about 5% high so as good as perfect (AC outlets are ~123 VAC). Had a little hum, ground loop, but since I had out my meter I put in my shorting jacks and measured the noise on the outputs 1.35mV & 1.44mV Left and Right respectfully.
I was surprised at the bass, quite good, actually sounded a little more solid than an EL34PP AMP I built using same tube compliment.

Next up is a Tele 12AX7 and RCA 12BH7 and then not sure yet with the outputs and let it play. Then a clean up on the wiring.

Also built one of David Gillespies EFB circuits which I need to test. Its already installed but not connected. I think I need to get some tightly matched tubes even though my board has individual VR's for each tube beforehand.
I have some matched EI's somewhere but could not put my hand on them yesterday. Not sure what I did with them.

Any suggestions for current production EL84's?
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Re: ST 35 Finally Powered.

Postby jgf » Tue Jan 21, 2014 12:03 pm

Not new production, but affordable: I'm running 6p14p-ev in my EFB-ized stereo 35, they work great! I think sovtek EL84M is equivalent. A while ago before installing the EFB circuit I had JJ's in there, they sounded good too, but tested well used when I replaced them.
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Re: ST 35 Finally Powered.

Postby andrewbee » Tue Jan 21, 2014 2:17 pm

Hi JGF,
Thanks for the response.

Sill cannot find my Ei's.

I have read about the 6p14p-ev but have never laid eyes on or heard one. I took a look at Jim McShane's site, the only matched quads I saw were the JJ's and Gold Lion re issues. The JJ's are good $ wise but the Gold Lions were $120.00 for the quad. I thought this was expensive. Went looking at a few other sites , Tube Depot and Kevin Deal and saw some EL84's for $150.00 each! Went back to Jim's but he is out of town for a few days.

Read a post from Jim on AA where he had a substitute for the 6p14p-ev or EL84 coming in soon so will contact him to see what he has in the pipeline. Will probably take a quad of the Gold Lions and maybe the new tubes if he has them. At current tube prices it seems to only make sense to buy extras and put away but don't put them away too well, you may not be able to find them like my E.I.'s (lol)

Did you notice a significant difference of sound with the E.F.B.? It certainly reads well technically and the figures seem to back it up.



Thanks

Andrew
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Re: ST 35 Finally Powered.

Postby jgf » Wed Jan 22, 2014 2:52 pm

Gold Lion seems to be the top of the New Sensor line, especially for hifi use, whether it's worth it for your system and your ears I don't know. All I've tried is what I listed, plus a random collection of ones and twos of various older American and European makes. You're probably seeing new old stock at the $150 price, that just doesn't seem necessary to me, I'll go with new production instead.

The EFB mod is a big difference in distortion, power, and bass slam. I like it. Some don't. I suggest you try it with the tubes you have now and see how you like it. Take heed of Dave's recommendation to add grid and screen stoppers to the power tubes. Are the sovteks you have now EL84 or EL84M? They might be the same as 6p14p-ev anyway. The SCA35 which I converted to the stereo 35 EFB circuit had 3 old "Made in Germany" EL84s in it when I got it, which on closer inspection look to be actually Russian. They sound about the same as the new quad I put in, but I firgured a new matched quad was a good idea.

Give Mr. McShane's recommendation an ear!
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Re: ST 35 Finally Powered.

Postby andrewbee » Thu Jan 23, 2014 11:15 am

Hi,
Yes the $150.00 were N.O.S. but still way too much. My Sovteks are not the M versions, at least they don't have an "M" on them, just the plain old cheap ones I got for A.E.S. many years ago as test tubes more than anything else as I had my favorites. Truth be told at this stage they sound fine. My board is the Rev "E" so the grid /screen resistors are in place. I have a concern about the grid resistors value which exceeds the recommended maximum for fixed bias operation. I seem to remember Dave Gillispie addressing this somewhere saying its okay as the published data is at maximum dissipation which would be true. I could always just change them to ~240K and double the coupling caps value, no big deal.

I am kind of on a roll so maybe this weekend I will connect up the E.F.B. and test if I get a chance. Once that is done I can consider the Gold Lions.

Andrew
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Re: ST 35 Finally Powered.

Postby andrewbee » Wed Jan 29, 2014 5:40 pm

diytube st35.jpg
Diytube ST-35
diytube st35.jpg (973.57 KiB) Viewed 9064 times
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Re: ST 35 Finally Powered.

Postby andrewbee » Wed Jan 29, 2014 5:42 pm

diytube st35 cathode bias.jpg
This is what it looked like on Sunday before last A.M. EFB board in but not connected. Sorry about the cellphone pics.
diytube st35 cathode bias.jpg (94.68 KiB) Viewed 9063 times
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Re: ST 35 Finally Powered.

Postby andrewbee » Wed Jan 29, 2014 5:46 pm

efb 2.jpg
EFB installed and running.
efb 2.jpg (92.77 KiB) Viewed 9061 times
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Re: ST 35 Finally Powered.

Postby andrewbee » Wed Jan 29, 2014 6:09 pm

Need to clean up the wiring and replace the spst power switch with a dpdt (I prefer to switch both live and neutral) and insulate the fuse leads etc. Also found the E.I.tubes. Have two matched quads..... almost. I found one quad and 3 of the other quad, of course the missing tube is enjoying hiding itself.

The EFB was easy, the quad is perfectly balanced for now ;) . I installed individual adjust pots for each tube but so far not necessary.

I reused the 10R resistors from E.G. R43 and placed in R17 however they are all 11.6R measured so after the tubes run in will adjust to compensate for the slightly higher resistance, at least the 4 resistors are consistent!

I can't say how it sounds in comparison to stock as it was stock for just a few hours and after the EFB installation just had it going long enough to verify operation, still sounds good to me. Hopefully will get sometime later this week to give it a listen and maybe replace the driver and phase splitter tubes at the same time.

Andrew
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Re: ST 35 Finally Powered.

Postby jgf » Thu Jan 30, 2014 1:44 pm

Congratulations on your successful build. It looks like you have an extra large power transformer and an added choke, that should improve the sound quality. One of the standard upgrades is a 12bh7 for the 12au7, if your transformer can handle the extra heater current. I haven't tried that myself, I'm using individual stereo 35 clone boards.
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Re: ST 35 Finally Powered.

Postby andrewbee » Thu Jan 30, 2014 3:57 pm

Thanks. Yes, power transformer (250mA) and choke (8H 200mA) are overkill. I have a 150mA power transformer and 5H 150mA choke to replace them with. I did not use them to begin with as they would both have been near the limit current wise (and particularly with an AB class amp you need a stout power supply) but with the EFB and lowered current demand I can use them now.

I have a 12BH7 at home, think its an RCA and some Telefunken 12AX7's so will be replacing the voltage amp and phase splitter tubes. I borrowed the two in there now from my EL34PP amp anyway so have to put them back.

Andrew
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Re: ST 35 Finally Powered.

Postby Shannon Parks » Sat Feb 01, 2014 5:12 pm

Datecode '66 on the Z565s? I love seeing that stuff. Good year by the way - my ruby red '66 Fury III will always be my first love.
Congrats on the build and EFB mod.

Shannon
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Re: ST 35 Finally Powered.

Postby andrewbee » Sun Feb 02, 2014 5:47 pm

Hi Shannon,

Thanks.

Date code? Not sure. They were cloth leads with 16R tap. I can barely make out what appears to be a stamp in white paint on the top of one transformers that appears to be P or F 11 and below it what might be 66 so you may well be correct. It is so light that its hard to read.

Don't know if you ever saw this before http://www.one-electron.com/Trans_Tests.html. Dated but still good information.

Really nice board you made available for us.

Andrew
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