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This is a cathode biased EL34 amp with a jcm 800 sort of setup. NOT the one i always post about, but one a friend has and it's the first one i built. there is a static like buzzing which only happens past a certain level of either gain or volume, tho the volume must be up a bit while it can happen with the gain quite low as long as the master is up a bit. It seems like it must be in the PI or beyond but i'm not sure. I have checked all coupling caps and they seem fine. If i pick the low e with a bit of gain to make it sustain, i can play with the master and make the buzz come and go as i find the point in the master's range at which the signal is strong enough to cause it, and It starts abruptly and cuts off abruptly while playing with the master. Tubes are new so i doubt thats it. Checked ot hit every solder joint in the amp.
Almost forgot....with no bypass caps on the power tube cathodes it doesn't do it. But i tried new caps of the same value (220uf) and even new 33uf's and with both the noise was there. But removing them removes the noise no matter how loud i go. That should be a key clue.
Almost forgot....with no bypass caps on the power tube cathodes it doesn't do it. But i tried new caps of the same value (220uf) and even new 33uf's and with both the noise was there. But removing them removes the noise no matter how loud i go. That should be a key clue.