issues with ac-30 build

[pineapple49]

hey guys i finished my ac-30 build a few months ago, ive gigged it a few times and then this morning while having a quick jam, the volume drops, i check out the tubes and they all seem fine, so i keep playing, about 20 mins later the volume goes back to normal for 10 mins then goes back to being quiet. i have a feeling the power tubes are going, there jj's, but they really havnt been pushed that hard. would there be any other problems i really just dont have enough time to sit down atm.

and also if someone could help me, the cut control doesnt seem to work properly, if turned a quarter of the way up the volume drops, then past that it makes annoying buzzy zippy sounds, is that normal??

the schematic i copied was from hoffman amps/el 34 world.

thanks guys please help me

[trevorus]

I would check for cold/broken solder joints. As far as the cut control, I suspect it's probably not wired quite right. I used a Vox style cut control in my Bogen conversion, and it's basically wired as a variable resistor and a cap of around .0047 uF between the sides of the phase inverter output after the coupling caps, but before the grid resistors.

[pineapple49]

ok i went over all my solder joints and they all seem good and solid, so im unsure of what to check next...and also with the cut control, the leads run pretty close to the heater wires, so im thinking thats the problem there.

[pineapple49]

i did a few measurements this morning... i have a B+ of 324 vdc, which seems a bit low for a gz34...and also i tried playing into the normal channel and it seems to stay on louder then the top....so either a rectifier or preamp tube do you reckon???

[jfutral]

Just to clarify, are you saying the normal channel works fine and the top boost channel is giving you the issue?

Not knowing what PT you have, I would think it is difficult to say if your B+ is low or not. But I could be wrong.

Joe