Princeton Reverb 65 Howling feedback

ICBM

adampeter said:

I tried both taking out the 12AT7, and also i tried a new 12AT7 in the driver, no change.

Also tried a different new tank, same issue
I guess i'm out of amateur avenues and need an amp tech?

Probably nothing but with the tank disconnected if i touch the ends of both rca cables the amp feedbacks

That’s normal.

My best guess at this point is something like a shorted cathode cap in the reverb return circuit which is creating too much internal gain when the pot is above 4 - but that’s definitely a job for a tech if you’re not familiar with checking and repairing stuff like that.

adampeter

ICBM said:

adampeter said:

I tried both taking out the 12AT7, and also i tried a new 12AT7 in the driver, no change.

Also tried a different new tank, same issue
I guess i'm out of amateur avenues and need an amp tech?

Probably nothing but with the tank disconnected if i touch the ends of both rca cables the amp feedbacks

That’s normal.

My best guess at this point is something like a shorted cathode cap in the reverb return circuit which is creating too much internal gain when the pot is above 4 - but that’s definitely a job for a tech if you’re not familiar with checking and repairing stuff like that.

Thanks mate, i will see who's recommended in my neck of the woods

nero1701

At this point, I'd be sending it back to where it came from. 

Wazmeister

Send it back mate… there are 100s of these out there to buy.

adampeter

nero1701 said:

At this point, I'd be sending it back to where it came from. 

Courier insurance has made this a very economical repair proposition for me

nero1701

Well, my offer still stands if you want to pop down.

adampeter

nero1701 said:

Well, my offer still stands if you want to pop down.

Thanks mate, it’s going to a tech tomorrow, I tried different tanks and valves so it’s something out of my skill set, will update thread on the outcome and if I’ve made a costly error or had a result 

Soreeyes

adampeter said:

Picked up a Princeton reverb 65 reissue, was delivered today, 
Cannot get the reverb above 4 without it howling and screeching, this happens regardless of guitar being plugged in, and positions of the other controls.
Checked the tank, took it out of the cab, check the tank connections, all did nothing to stop the issue.
Apparently this didn't happen before posting
Any ideas of what to try next before it gets sent back?

mine did that, I wrapped the tank in bubblewrap, put it back in its cover and now it doesn't 

adampeter

Update for those interested, Tech said its Reverb Transformer, apparently if you ground out the centre tap it stops the oscillation (none of that means much to me), so this part is getting replaced

ICBM

adampeter said:

Update for those interested, Tech said its Reverb Transformer, apparently if you ground out the centre tap it stops the oscillation (none of that means much to me), so this part is getting replaced

There isn't a centre tap on a Fender reverb transformer.

If it has one, someone has already replaced it and used the wrong part.

nero1701

ICBM said:

adampeter said:

Update for those interested, Tech said its Reverb Transformer, apparently if you ground out the centre tap it stops the oscillation (none of that means much to me), so this part is getting replaced

There isn't a centre tap on a Fender reverb transformer.

If it has one, someone has already replaced it and used the wrong part.

Interesting twist to the tale!!!

adampeter

ICBM said:

adampeter said:

Update for those interested, Tech said its Reverb Transformer, apparently if you ground out the centre tap it stops the oscillation (none of that means much to me), so this part is getting replaced

There isn't a centre tap on a Fender reverb transformer.

If it has one, someone has already replaced it and used the wrong part.

mmm, interesting, the plot thickens

adampeter

nero1701 said:

ICBM said:

adampeter said:

Update for those interested, Tech said its Reverb Transformer, apparently if you ground out the centre tap it stops the oscillation (none of that means much to me), so this part is getting replaced

There isn't a centre tap on a Fender reverb transformer.

If it has one, someone has already replaced it and used the wrong part.

Interesting twist to the tale!!!

I suppose there is always the chance the tech isn't being totally upfront

adampeter

Update, amp is back, has a new reverb driver transformer and he replaced a 100k resistor on the phase inverter which was adding distortion to the decaying notes, anyway amp now sounds fantastic and the tech bill was very reasonable