The vibrato channel hums when the volume is around 2 o'clock and higher. Also it is not as loud as the normal channel (no hum there, even all the way up). Voltages on all plates are in line with the schematic (factoring in modern line voltages). I don't have a tube tester and no EF86 to substitute but I would like to eliminate the tube as the cause. I did short the input to ground just in case it was the jack but it still hums. I wonder also if the ECF82 may be the problem. The pentode side of that tube is the oscillator for the vibrato and I suppose it could introduce hum as well. I wonder if It could be pulling the volume down too. On these amps you have to pull the chassis to get to the tubes. I will pull that tube when I get the chassis out and see if the hum goes away.
This is a sweet sounding little amp with great vibrato. It needs a voltage selector switch which I have no idea where to get.
60s Vox AC-10 Twin issue
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