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In Reply to: RE: So what have I got wrong this time? posted by vinnie2 on May 24, 2016 at 08:48:37
I now have an all AC filament heated 28-26 DC 45 amp sounding great.
I found I did not need a cap between the two 26 tubes. and I DID NOT bypass the Rk on the first 26. This pretty much follows all the twin input tube sections I found in the archives.
Again here is a copy of my public Domain schematic for my working 26-26 DC 45 stereo amp.
Have fun
Willie
Follow Ups:
Willie,Choke off your rectifier is listed as 320 mHY or 0.32 Hy. If its a Traid, it must be a C-40X and NOT a C-56U as you have denoted on your schematic.
WHICH Traid is it ???
Triad C-56U as I recall is used for " flywheel " supplies ala Pasternak, which is 35 mHY at 2 A. and 0.79 Ohms.
Your notations on "D-Link" caps needs to be corrected to "DC-Link" caps, so people understand. eg :
http://www.vishay.com/capacitors/film/dc-link/
WIMA makes em too.
Where IS Henry Pasternak, Ray Moth, and the ole gang of well-wishers ??
Lovely to my eyes, ( and your ears most likely ), to see you using all sub 10 Ohm DCR Ls in your filtering / supply DrummerWill. You need to teach Vinnie that technique.
Do all 'de Forum members notice you used doubled-up resistors on ALL plates and cathodes, to get the most dynamics possible...closely matched to each other ???
This build technique was likely first seen decades ago in the KILLER MFA Luminescence RIAA ( 70 pound ) preamps. A high-water-mark I'm told in preamp design and performance.
Jeff
Edits: 05/26/16 05/26/16 05/26/16
I am confused Willie. You say you did not need a cap between the 26's, but your schem shows one. Or is this not the schem for that amp?
I finally do have mine working again, but now I need to do some tweaking.
Switching over to dc heating on my 26 preamp allowed me to use ac heating on the amp filaments with virtually no hum. Made a big difference.
Might have to try some of your changes too. Sounds interesting!
Edits: 05/26/16 05/26/16
Oops.... I knew I should have looked at my own schemo , before I tried to tell someone what to do. You are correct, only DC to the 45 !...
Dear Dr. LowMu, the L1 choke is a Triad C-56U as labeled. My mistake was designating it as a 320 mhy choke, it should be labeled as 350mhy. Thanks for pointing that out.
Have fun !
Willie
Triad C-56U is only 35 mHY, so its the start of a Henry Pasternak Flywheel ...fine !!
Rated DCR is only 0.79 Ohms, Current rating is 2 A.
Jeff
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