Valve amp, little used then stored for 3 years now very low level wanted, undistorted output and constant buzz, minimum wiht middle setting of A/AB pot on rear. Good signal out of SEND and bad output from test signal in RET, so PA problem. Nothing seen weeping nor dodgey solder. I was hoping S/R bypass switch corrossion but not that.
I've not fathomed the schematic, how the relay functions. Looks as though 1 of 3 relays switch over from external to internal and the footswitch socket seems to be involved in that, so perhaps corrossion there or a stuck relay.
Looks as though corrossion of a contact on ECC83 driver valve and the Return tip contact
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