My 1974x amp is quiet when nothing is plugged into it, but as soon as I plug my intrument cable into the non-tremolo channel, I get this awful cyclic noise. Does anyone know what to do? I replaced the ECC83 tubes one by one (testing it between each tube replacement), but it didn't fix the problem.
Here's a video of my problem.
Thank you for details on you issue, it sounds like it could be a power supply issue, have you tried another guitar and lead, we would recommend it is looked at by an engineer to check this over.