Fender Deluxe Reverb High Pitch Squeal when turned on

[nevetslab]

This is the other Fender Deluxe Reverb I found in the road case that had the previous one I just replaced the heater fuse on/posted about. The description of the problem was familiar, so looked thru my service notes spreadsheet, and found it was the same one I saw May 7, 2021, just as I was about to start the work on the Mike Campbell vintage amp restoration project. I didn't get the amp to misbehave for me at all. I then had looked at the history of this amp, and found it had been sent to the shop with the same problem back in October 2020. Never heard the amp produce it then, nor in October 2020. Looked for other Fender amps having that problem, finding it in a Princeton Reverb, a Twin Reverb with a whistle, and a Vibrolux Reverb with reverb squeal, that had so much gain in the reverb circuit, I turned it down 10dB. But, this seems to be one of those bad pennies that only misbehaves outside of the realm of a shop.

I moved the amp's AC Mains connection from my variac/power analyzer to a different source, that does pass thru an older Weston Ammeter, which can be bypassed, with the mains being monitored with an older Weston meter...opposite wall in my narrow/long shop. As before (both times), repeated powering up cold start has yet to have the problem show up. This being the third time back for the same symptom, what am I missing? All that is required to have it occur is to plug it in, power up, let it warm up for a minute or two, and switch out of Standby. Instant loud squeal. Reverb set around 2-3 on the front panel. Not set for Surf Music...just mild reverb. If it is from the Reverb circuit.

I can think of more effective use of my time than trying to induce this repeat-offender (from the same Guitar Dept's AC Mains source) to produce the offending squealing. Is it selective with regards to where it's plugged into AC Mains?

[nevetslab]

When I sent an email to the current manager of the Guitar Dept, as well as the previous mgr who I had been working with while I was set up in my temporary shop at the inventory warehouse, asking about the date that was taped onto the top of this amp, being 4/12/21, when I had received it and last serviced it May 7, 2021. The tape had been left on the top of the amp, which was confusing finding it now in August. Several of the Guitar Dept staff had hear it, and reliably occurred switching out of Standby.

I never heard it happen. It occurred to me after sending it back that every time I looked at it, I had it on the test bench and NOT on the concrete floor. Every time they looked at it, it was on the floor. I don't know if that has anything to do with it. And, to my knowledge, it's only done this there in the Guitar Dept, plugged into the same AC mains. I'm not ready to believe there's a problem with their AC mains, as I was powered from a similar branch there in that building.

So, I'm still waiting for more of this misadventure to continue.