I'm getting ready to button op a hybrid push-pull design that uses a sand-state front end with EL84 output. At present I'm using the JJ tubes. My power supply transformer came from a Fisher console, and its B+ is on the frisky side of 400V. This may quiet down a bit when I get around to loading it down, but in case it's still on the high side, can I preserve tube life by lowering the screen voltage and observing dissipation limits?
I think 400V B+ is no problem as long as screen is held at about 300V and plate dissipation is observed. SY somewhere here stated of obtaining 25+W using 500+V B+ and 300V Screen on his RLD. Roger Modjeski's RM10 is 35+W with 700V B+ and 350V screen with an estimated 5000-10000hr tube life due to low 15 ma bias.
I built an amplifier a few years ago that ran EL84 / 6BQ5's with 430 volts on the plate, 320 volts on the screen, and a 6600 ohm OPT. Power transformer was an Antek toroid.
It made 60 watts per channel with 4 tubes in PPP and still has the same tubes in it (Baldwin branded Sylvanias from an old organ amp) . JJ's, old Sylvania or RCA 6BQ5's were the only tubes that I tried that lived at those levels. Modern Russian or Chinese stuff red plated, red screened, or just went poof!
It made 60 watts per channel with 4 tubes in PPP and still has the same tubes in it (Baldwin branded Sylvanias from an old organ amp) . JJ's, old Sylvania or RCA 6BQ5's were the only tubes that I tried that lived at those levels. Modern Russian or Chinese stuff red plated, red screened, or just went poof!
Well George, I was also astonished when I first found out, and RM10 is still Roger's current product. In 2009 he also claimed "I have tried EL-84s from Russia, China, USA and Eastern Europe." I guess for PP EL84, he went a bit further than the rest of us. You can find more details here, perhaps you can dig something useful, some of the things he said are over my head.
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