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Post subject: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Tue Jun 28, 2011 12:58 pm
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As i read in some of posts here and there, a lot of PrincetonReverb (PRRI) amps that suffer from hum issues only when the reverb is engaged, especially noticeable when the knob is anywhere from 3 to 10, even when no instrument is plugged in at all.
Some say it's an issue that can maybe be resolved by replacing the tube before or after the reverb circuit 12AT7 or 12AX7A, and some others say that it could be the reverb tank feeding back.
Can anyone please confirm how he dealt with this issue?
My PRRI is dead quiet when no reverb is engaged but, is too noisy with the reverb past 3, practically unusable for recording purposes.
Any feedback greatly appreciated.
thank you in advance


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Post subject: Re: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Tue Jun 28, 2011 2:06 pm
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Is the reverb tank correctly installed?

It should rest upon a 1/8" sheet of multi-layered cardboard, within a leatherette bag, and the bag secured to the bottom of the cabinet via a neoprene rubber strap. The two screws holding the strap should only be tight enough to hold the bag with the tank in it in position. Cables to and from the tank should be routed down the right side of the cab (as viewed from the rear) using nylex strain reliefs to keep them isolated from the speaker's magnetic field.

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Post subject: Re: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Wed Jun 29, 2011 2:05 am
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Thanks for the feedback!
will try your solution even though i can't really get the cardboard thing. I am not at home at the moment so i can't see if there is already a cardboard installed. If not I'll install one. Is this necessary for magnetic isolation as well? If so, shouldn't it be installed on top of the reverb tank? Will try and keep you posted.
thanks again!

By the way, i haven't made any changes to the amp whatsoever. If the tank is wrongly installed, it's a bad quality control on fender's behalf.


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Post subject: Re: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Wed Jun 29, 2011 9:22 am
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The cardboard acts to isolate the tank from cabinet vibrations. If the physical installation of the reverb tank and associated components is correct then your problem lies within the chassis itself (assuming it's not the tank that's bad).

Arjay

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Post subject: Re: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Wed Jun 29, 2011 1:41 pm
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Well, i opened up the leatherette bag, and all seems ok. The cardboard is there, and the cable is neatly tied and screwed on the right side of the cabinet.
Nevertheless i investigated the issue of magnetic interference by the speaker, by removing the tank from the amp cabinet and placing it the furthest possible from the amp itself (as far as the cables permitted).
There was no change whatsoever on the reverb hum, so that eliminates the theory of speaker magnetic interference to the reverb tank.
Next suspect is faulty tubes. Specifically the ones that deal with the reverb circuit since without reverb the amp performs perfect. Do i try to replace the 12AT7 or the 12AX7A?
If this doesn't work then it could be the reverb transformer...
Any ideas?
thank you in advance


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Post subject: Re: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Wed Jun 29, 2011 2:03 pm
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Either the driver (12AT7) or the recovery tube (12AX7A) might be the cause -- try replacing them individually with known good tubes and note your results. If not a tube per se, the symptoms may yet be tube-related......cold solder joints on a socket, incorrect cathode current, bad coupling cap or resistor, etc. I'm dubious that the reverb tranny is at fault.

Arjay

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Post subject: Re: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Wed Jul 06, 2011 1:42 pm
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First tried to replace the recovery tube (tube 4: 12AX7A with another tube of the same type that was siting in slot 2) no change.
I then bought an electro harmonix 12AT7 and replaced the stock tube ( slot 3) with this one. The hum is still there, (maybe slightly less but then again my ears might be tricking me).
So the problem is still there...
What would you suggest i should check now?


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Post subject: Re: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Wed Jul 06, 2011 9:40 pm
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fotofono wrote:
What would you suggest i should check now?


The Yellow Pages for a qualified amp tech in your area. If the amp is still under warranty, take it to an authorized Fender service center. Bring the original bill of sale or sales receipt with you.

Arjay

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Post subject: Re: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Wed Sep 18, 2013 8:23 pm
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I have had a similar problem with my PRRI. The reverb does not work. Took amp back to Fender Dealer and problem would not occur in shop, very slight hum but reverb worked. Damn intermittent problem.

A day or so later reverb is gone again, only hum. The noise seems to increases in volume when turning up reverb dial. No reverb just hum. I have checked out the tank, everything is set up as it should be.

I thought it was wire and found that when I moved the stock wire from amp to reverb tank I got alot of noise. After replacing cable with after market thing I did not get any noise from moving the wire. It work for a while and then next day it starts humming again. Issue comes and goes.

Any ideas on this one? It is a real disappointment.


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Post subject: Re: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Wed Sep 18, 2013 9:18 pm
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Same hum with a guitar plugged in or not?


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Post subject: Re: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Thu Sep 19, 2013 3:12 am
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Yes, hum is with or with guitar plugged in


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Post subject: Re: Princeton Reverb Reissue (PRRI) reverb hum
Posted: Mon Nov 04, 2013 8:03 am
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Did either of you guys ever get your issue resolved? I recently returned a PRRI for having the same issue. Not long after, I ran across a couple of forums where Princeton owners reported fixing the problem by changing the rectifier tube. I'm curious whether you guys got the issue sorted out. And if so, was the rectifier tube indeed the culprit?


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