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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Failing and Exploding EH 7591s posted by Lee of Omaha on May 15, 2015 at 09:59:22:
What was the cathode current the tubes were running at? It is entirely possible the tubes were running over their dissipation limit which will cause what you described. With 440 volts or so on the plate 40 ma. per tube is as hot as I'd go.The stock 800C has non-adjustable bias, did this unit get a bias adjustment setup?
Also, were the 330K grid resistors and the .047 output coupling caps replaced with proper values? I have been saying for years that this needs to be done. Was it done on this amp?
Unless you did the above, the tubes were not likely the cause - they were the victims.
FWIW, I have near zero trouble with the EH. But I only sell cool biasing 7591As, many are too hot to be used in units like the 800C especially with todays higher line voltages. And I always recommend the grid resistor and coupling cap value be changed, and it's not a bad idea to make the bias adjustable.
I would also add screen stopper resistors and 10 Ohm cathode resistors if I was inside an 800C.
Edited to fix typo
Edits: 05/15/15
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- RE: Failing and Exploding EH 7591s - Jim McShane 11:23:32 05/15/15 (0)
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