Stock ST-35 power supply choke question

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Stock ST-35 power supply choke question

Postby Mossback » Sun Nov 02, 2008 1:25 am

My first post. Thanks for all the useful information here it has been very helpful to me.
Recently I bought an unbuilt Dynakit ST35 sans transformers and PS off epay. Mike (MagneQuest) made me a pair of nickel output transformers four or five years ago so I am now building a “new” old ST-35. It should be working in a few days.
After the Dynakit arrived I discovered this forum and the DIYtube ST-35. I may build the DIYtube ST-35 later using the nickel outputs and a hot rod PST if they sound as good as I think they will.
I have a power supply question and hope someone can please help me.
In my stock ST-35 can I replace the 50 ohm 10W power supply resistor with a ST-70 C-354 choke? This choke has been used in the Diytube ST-35 from what I have read here. Ned is selling an enclosed choke on epay that would look good atop the stock amp.
Thanks Mossback
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Postby Ty_Bower » Sun Nov 02, 2008 6:11 am

Yes, the C354 choke can drop right into the ST35 power supply in place of the 50 ohm cemented resistor. Most people do not report much audible difference. I've assembled two ST35 amps, neither of which have the choke. I can't say I miss it much. I suspect Shannon's power supply kills most of the hum with lots of capacitance. What little is left probably gets canceled out in the push/pull finals. Somewhere I read the choke might help reduce solid state rectifier switching noise. I wonder if there is any merit to that.

If you're looking for something on the cheap, I think a Triad C-24X might be a close substitute for the C354. They're under $8 from Allied Electronics.

http://www.alliedelec.com/Search/Produc ... KU=9671004
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Postby Mossback » Sun Nov 02, 2008 10:10 am

Thank you Ty. I do have an old beat up used one to try first.
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Postby EWBrown » Mon Nov 03, 2008 5:35 pm

I got ahold of one of those unbuilt ST35 kits five years ago, and built it up 100% stock original, in order to use it as a "control" to which other amps could be compared.

BAck to the PSU choke question:

Hammond also has a C-354 equivalent in their "156" series of chokes. Just look for 1.5H, 200 mA, with 56 ohms DCR (maybe 156R, I don't have my catalog here in NH).

The original Dynack ST35 had a just barely adequate power supply, and the original shared 95 ohm cathode resistor was a real "penny pincher", I'd go with individual 390 to 430 ohm, 2W resistors, bypassed with 100 to 470 uF, 35V cap for each 6BQ5. THe Triode ELectronics PA-774 is good unit, and fits the original chassis perfectly. And it runs somewhat cooler than the original PA774s.

Those MQ 565s are "awesome" I've built up a Rev D DIY35 with the MQs and Auricap coupling caps, and it sounds truly , and I did use the C354 choke in place of teh 50 ohm 5E resistor. I built it up on one of the now-unobtainable "soundtastick" chassis, however TRiode has a very similar stainless steel chasis. .

There are "aftermarket" ST35 cap boards available on e-bay, abd there is room on the original ST35 chassis to mount the C354 and cap board on top of the chassis, between the two OPTs.

HTH

/ed B
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Postby Mossback » Thu Nov 06, 2008 4:40 am

Thanks for the useful tips. :) I will hold off on the R13 and C8-D EL84 cathode rework because I may sell this one and swap the MQ’s over to a DIYtube ST35 board.
I did use the Triode PA-774. I read about that here before starting my project.
Ned has a nice shielded choke on epay so I ordered it. It will fit atop the case safely and look stock.
OK good, you liked the MQ output I figured they should be sweet. Were yours nickel? I hope to finish it this week.
Thanks Mossback
PS Thanks for the cathode info I never would have thought to do that.
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Postby EWBrown » Thu Nov 06, 2008 10:51 am

My MQ565s are not the nickel core version, but they still sound beyonf great! The handcrafted quality definitely shows up well with these. The original Dynaco Z565s and the Triode Z565s are also very good, and at a fraction of the cost of the MQs, they deliver a very good "bang for the buck".

I have had "mixed" results with the later model Japanese made, plastic insulated lead OPTs, as they tended to be more ""variable" in quality.

I like the shielded / enclosed chokes, I haven't yet tried the C354 version, but I have used the 4H / 90 mA / 110 ohms DCR "Fender" chokes from Triode in my 13EM7 SET amps, with very good results.

With a bit of layout and grounding care, using Trafomatic toroid power tannies, and the Fender choke, I was able to attain hum-free performance, even with series-connected AC filaments.

/ed B
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