My twin reverb, which is based on the Hoffman AB763, sounds wonderful (other than nearly no tremolo which we have gone over a dozen times) but when I turn it on, after about 5-10 minutes a wash of band limited pink noise comes up. Its not super loud but its quite obvious to me. SHHHHH not SSSS. Its not there when the amp is cold (but working) so it must be something getting hot. Any advaice on where I should expect to find this? This sort of thing drives me nuts.
My Princeton Reverb which is mostly stock bbut has the reliability mods has a 60Hz hum with some harmonics, but not much, on the REVERB return. This is there if the reverb switch is on or off. It is there if the reverb return is unplugged. The noise increases with the reverb plugged in, but that is to be expected. What is not acceptable is the hum that is just steady and increases with volume just by turning up the knob. The reverb otherwise sounds great. The reverb transformer is slightly microphonic but it hasn’t proven to be an issue. Basically if I tap hard on it, it will put a bit of sound into the springs which returns as reverb. This issue with the hum is on the return side. It is a very stock layout since the board is a Mojotone kit. I put the amp together in 2014. All the resisters are metal film and the caps are mostly orange drops, sprague, and it has the stock cap can which I think is TAD. The amp is nearly dead silent other than the tiny bit of hiss, if the reverb return is turned all the way down. Clearly I am picking up hum in the reverb recovery. Where should I be looking for that?
Topic: 2 issues, 2 different amps (Read 1574 times)