new deluxe reverb style reverb oscillation

[imo1]

Still not sure exactly where the feedback loop is

Fender reverb circuit has some feedback. If there's 20mV signal on the recovery tube grid and the reverb pot is fully turned up then about 1mV gets fed back to the reverb driver tube grid. Even small changes to the circuit can make it oscillate.

I responded to Martin in another reply with a similar, albeit less technical, response. I have a bunch of original Fender blackface amps, and part of that sound is built into the circuit. Mine is stable now, and the issue I had, was simply having an input cap an order too big, with was creating the feedback oscillation.

[imo1]

Eureka!

So obvious now that I can see it. I had a .033 instead of a .0033 off the plate of the recovery valve. Makes total sense. It was letting way too much reverby low end through and the circuit

i saw that was your cap 0.0033 too big for the value

I didn’t, until I did!

[martin manning]

Still not sure exactly where the feedback loop is

Fender reverb circuit has some feedback. If there's 20mV signal on the recovery tube grid and the reverb pot is fully turned up then about 1mV gets fed back to the reverb driver tube grid. Even small changes to the circuit can make it oscillate.

Grounding the pedal jack center pin (recover stage grid) didn't kill it tho...

[martin manning]

I feel like the “loop” was too much low end into a circuit that already, under stock circumstances, pushes the limits of the circuit. The fender blackface circuits with reverb on 10 sound like they are on the verge of feedback. I think my circuit is operating properly. It sounds exactly like any of my blackface Fenders that I have.

Sounds like it's all good now. That low frequency oscillation was an unusual occurrence, not something I've heard before. You've got it working properly now so no problem keeping the sockets even though they do force a different lead routing.

[imo1]

I wanted to post an update, in case it has any bearing or is helpful for anyone else.

First thing- I had a brand new, faulty bias pot. It’s crazy, but I’ve had more issues in my new amps than I have in a career of countless old amps. Really crappy quality control. I currently have a 10k audio pot, just to make sure circuit is solid and it’s holding well. I have a couple of chassis mount 10ks on order.

The other issue I was having was a low level buzz with the reverb maxed. It wasn’t bad, but I knew I could get it quieter. I tried a million different things, but found that running a ground wire from the RVB output rca jack ground back to my ‘BC’ ground, again following Martin’s ground scheme, was the quietest I could get the amp.

I’m so happy with the amp, that I’m using it as a template for some work on my ‘72 Deluxe, which I already loved quite a bit.

[martin manning]

...running a ground wire from the RVB output rca jack ground back to my ‘BC’ ground, again following Martin’s ground scheme, was the quietest I could get the amp.

Do you mean the RCA jack that connects to the tank input or the one that connects to the tank output? Are your RCA jacks isolated from the chassis?

[imo1]

It's the tank output RCA ground, the point where the 220k cap grounds from the reverb pedal. I am using standard, non insulated jacks.