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In Reply to: piercing sound from amp posted by blur on April 14, 2003 at 20:27:49:
If so try feeding the amp a 1K square wave and see how the output looks. If the leading edge has a peak, which I expect, you might wish to play with the feedback loop or to "roll off" the first stage with a cap from plate to ground. But without some test gear you are stumbling around in the dark.
Russ
Follow Ups:
hi russ,thanks for the reply. too bad i don't have access to a scope. the caps he used wimas. i changed some of them to auricaps but the problems with the highs are still there. there are still some wimas in there. wondering should i change them all?
but then you are right. it could be feedback. so do you mean increasing the amount of feedback? what do you mean by rolling off the first stage? cap from plate to ground? or is it cap from grid to cathode?
thanks.
blur
Well like I said without test gear you are shooting in the dark. Assuming everything is correct and in good working order then slightly reducing the feedback might help but again without test gear....OR you can "compensate" by rolling of the voltage gain stage high Hz with a cap from plate to ground....some use one from plate to cathode. Do a web search for compensation of tube circuits. This is something you need to reasearch before you try implementing. Putting the wrong parts in the wrong place can lead to diaster. Sounds like you need to find someone local who can help. Any audio clubs....ham radio guys? Do keep in mind that your problem may be entirely different.
Wish I could help more,
Russ
Russ,Have you tried biasing the 6L6GC a bit hotter? Then check the tone. (-) 36 volts may be a bit cold, depending on the plate voltage used.
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