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I've got a 1992 Rose Morris "Vintage" AC30 here. The nearest schematic I could find is this one:
http://www.voxamps.com/downloads/circuits/ac30vrev.jpg
(This is from the official Vox Support site. It's partially hand drawn and the numbering doesn't correspond to this amp. But it does seem to be more or less the same circuit.
The amp has a low level pop and crackle similar to the sound you get from a deteriorating carbon comp resistor.
I've pulled the valves one at a time, and it seems to dissappear when I pull V6, which is the ECC81 which drives the reverb.The reverb recovery gain control doesn't have any effect on the sound when its there.
I've tried poking with a chopstick. Found and replaced several microphonic ceramics.
I've tried replacing resistors around V6. I've tried replacing the B+ dropper resistors
I tried a fresh set of valves.
I note that the schematic shows that ECC81 driving the reverb transformer in push pull with 11 ohms of cathode resistance. That seems a little low. Vk is around 2V so each half is conducting 100mA at idle...
http://www.voxamps.com/downloads/circuits/ac30vrev.jpg
(This is from the official Vox Support site. It's partially hand drawn and the numbering doesn't correspond to this amp. But it does seem to be more or less the same circuit.
The amp has a low level pop and crackle similar to the sound you get from a deteriorating carbon comp resistor.
I've pulled the valves one at a time, and it seems to dissappear when I pull V6, which is the ECC81 which drives the reverb.The reverb recovery gain control doesn't have any effect on the sound when its there.
I've tried poking with a chopstick. Found and replaced several microphonic ceramics.
I've tried replacing resistors around V6. I've tried replacing the B+ dropper resistors
I tried a fresh set of valves.
I note that the schematic shows that ECC81 driving the reverb transformer in push pull with 11 ohms of cathode resistance. That seems a little low. Vk is around 2V so each half is conducting 100mA at idle...