Princeton Reverb 65 Howling feedback

adampeter

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?

Wazmeister

Adam,

If the tank is in a cover, try taking it out...

adampeter

Wazmeister said:

Adam,

If the tank is in a cover, try taking it out...

Thanks @Wazmeister but i did try this, took out the bag, check connection and springs, etc, checked feet and cardboard, 

Alex2678

I’ve seen people talking about the transducers coming loose, not sure if that’s what it might be but could be worth a google 

noisepolluter

Have you tried a different 12at7 reverb driver/12ax7 recovery valve? (I think it’s that way round)

adampeter

noisepolluter said:

Have you tried a different 12at7 reverb driver/12ax7 recovery valve? (I think it’s that way round)

I haven't but will try this

adampeter

Alex2678 said:

I’ve seen people talking about the transducers coming loose, not sure if that’s what it might be but could be worth a google 

will have a google mate, ta

snowblind

Sounds like something has gone very microphonic. Start by just tapping the valves to see if it a bad tube although this isn't necessarily the cause. If the tubes check out ok then just tap around on the board. I had a bassbreaker which rang like a bell if you tapped on one end of the board. It was just a bad joint on a capacitor but anything that allows mechanical interaction can cause the kind of feedback you describe. 

nero1701

I'm based in Ipswich, not far down the 14.

I've the 68 princeton, feel free to give me a shout to pop down with it. You can try my tank, I've a few spare valves which you can use to check. 

ICBM

Try the valve first - it will be the recovery valve if it’s affected by the control level - the valve is the 12AX7 next to the reverb transformer on the side nearest the power valves. If you don’t have a spare, swap it for the one next to the power valves which is the phase inverter and tremolo driver (the same half as the reverb recovery is the tremolo).

If it’s not that, something may have come loose in the reverb tank.

TeleMaster

Is it used or new? 

adampeter

nero1701 said:

I'm based in Ipswich, not far down the 14.

I've the 68 princeton, feel free to give me a shout to pop down with it. You can try my tank, I've a few spare valves which you can use to check. 

Thanks bud, will let you know if i need your help

adampeter

ICBM said:

Try the valve first - it will be the recovery valve if it’s affected by the control level - the valve is the 12AX7 next to the reverb transformer on the side nearest the power valves. If you don’t have a spare, swap it for the one next to the power valves which is the phase inverter and tremolo driver (the same half as the reverb recovery is the tremolo).

If it’s not that, something may have come loose in the reverb tank.

Thanks mate, will try this out

adampeter

TeleMaster said:

Is it used or new? 

used

adampeter

Update- tried a new 12Ax7 in the recovery spot as per @ICBM no change.
Checked over the tank, looks ok, certainly nothing obvious.
Mucked around with the controls and found the following.
Even with the volume on 1 the feedback is there once the reverb is past 4, the volume has no effect on the loudness of the feedback.
Knock around on the tubes, does nothing, tubes all look fine to me ( being me probably means nothing)
If i touch both the springs in the tank the feedback stops, if either one is no touched the feedback starts
If i listen VERY hard i can hear the trem in the background (i think) this seems to be sympathetic (if thats the correct word) with the feedback 
Gut feeling is the tank, is there a simple way to check this?



 

ICBM

The volume will have no effect on the feedback since the volume pot is before the reverb circuit. The tremolo should affect it since the tremolo is afterwards.

If you don't have a spare 12AT7, try removing the driver valve - the one on the other side of the reverb transformer. I don't think it is this, but it's worth eliminating since it's so easy.

adampeter

ICBM said:

The volume will have no effect on the feedback since the volume pot is before the reverb circuit. The tremolo should affect it since the tremolo is afterwards.

If you don't have a spare 12AT7, try removing the driver valve - the one on the other side of the reverb transformer. I don't think it is this, but it's worth eliminating since it's so easy.

Don’t have a spare 12AT7, do you mean just removing the driver valve and trying the amp without anything in it place? I do have another 12AX7, could I try that in the driver spot?
TIA

ICBM

adampeter said:

Don’t have a spare 12AT7, do you mean just removing the driver valve and trying the amp without anything in it place? I do have another 12AX7, could I try that in the driver spot?

Just remove it - don't put a 12AX7 there.

vivalacoulter

I had something similar with my supersonic, I insulated the tank from the cab with some foam sheeting between the two on a whim and it resolved my issue.

adampeter

vivalacoulter said:

I had something similar with my supersonic, I insulated the tank from the cab with some foam sheeting between the two on a whim and it resolved my issue.

Hi mate

I’ve run the tank as far as possible away from the cab and sat it on carpet, etc, seems that it does extact the same thing regardless of position 

adampeter

ICBM said:

adampeter said:

Don’t have a spare 12AT7, do you mean just removing the driver valve and trying the amp without anything in it place? I do have another 12AX7, could I try that in the driver spot?

Just remove it - don't put a 12AX7 there.

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