Fender PRRI squeals on high volume

keliway

Member
Messages
3
So I have a fairly new Fender Princeton Reverb Reissue, after some some time at bedroom level it was time to crank it. Exactly after 5 on the volume knob there is a terrible squeal that starts with a crackling noise and changes frequency slightly as I turn the knob. It stops after around 8-9. This squeal appears always, even with no guitar plugged in and reverb and vibrato off. Usually I would think it’s a preamp Tube issue, but no - I replaced all tubes one by one and the squeal is still there. Also all tubes are shielded and not microphonic. I also cleaned the volume knob and tube sockets with no success.

Also tried different wall outlets and cables. If I connect it to my spare 1x10 cab the squeal is still there.

Before sending it back for repair (which will take at least 6-8 weeks according to the shop) I would like to fix that problem by my own. I also have another output transformer for a Princeton that I would try if nothing else helps.

I can also take a short video if that helps anyone.

Did I miss out on anything?

Maybe helpful, if I turn on the vibrato when it squeals, the squeal is vibrating just like the guitar signal - same for the reverb. That’s why I’m assuming the issue is in the pre amp area, maybe even before V2?
 

mikey69

Member
Messages
852
wow that is horrible, never experienced that before, wish I could help but it maybe better to let the warranty repair center take care of it, if you mess with it too much it may void the warranty, which would suck ..the local shop didn't have any ideas? maybe time for a new shop ..most good shops have an amp guy that can do some basic trouble shooting from experience and could swap out some power tubes for example to help avoid being without you amp for 2 month
 

esowden

Platinum Supporting Member
Messages
270
So I have a fairly new Fender Princeton Reverb Reissue, after some some time at bedroom level it was time to crank it. Exactly after 5 on the volume knob there is a terrible squeal that starts with a crackling noise and changes frequency slightly as I turn the knob. It stops after around 8-9. This squeal appears always, even with no guitar plugged in and reverb and vibrato off. Usually I would think it’s a preamp Tube issue, but no - I replaced all tubes one by one and the squeal is still there. Also all tubes are shielded and not microphonic. I also cleaned the volume knob and tube sockets with no success.

Also tried different wall outlets and cables. If I connect it to my spare 1x10 cab the squeal is still there.

Before sending it back for repair (which will take at least 6-8 weeks according to the shop) I would like to fix that problem by my own. I also have another output transformer for a Princeton that I would try if nothing else helps.

I can also take a short video if that helps anyone.

Did I miss out on anything?

Maybe helpful, if I turn on the vibrato when it squeals, the squeal is vibrating just like the guitar signal - same for the reverb. That’s why I’m assuming the issue is in the pre amp area, maybe even before V2?

Sounds like a microphonic tube - power tubes can be microphonic as well. Could be a microphonic component but that tends to be a bit on the rare side.
 
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Webfoot

Silver Supporting Member
Messages
2,924
I had something like that on a new PRRI and it was not tube based but was a function of the reverb when set to high. Did the bench thing but it was never really solved and did not want to spend money replacing everything non tube. Best of luck.
 

guitarjazz

Gold Supporting Member
Messages
24,442
So I have a fairly new Fender Princeton Reverb Reissue, after some some time at bedroom level it was time to crank it. Exactly after 5 on the volume knob there is a terrible squeal that starts with a crackling noise and changes frequency slightly as I turn the knob. It stops after around 8-9. This squeal appears always, even with no guitar plugged in and reverb and vibrato off. Usually I would think it’s a preamp Tube issue, but no - I replaced all tubes one by one and the squeal is still there. Also all tubes are shielded and not microphonic. I also cleaned the volume knob and tube sockets with no success.

Also tried different wall outlets and cables. If I connect it to my spare 1x10 cab the squeal is still there.

Before sending it back for repair (which will take at least 6-8 weeks according to the shop) I would like to fix that problem by my own. I also have another output transformer for a Princeton that I would try if nothing else helps.

I can also take a short video if that helps anyone.

Did I miss out on anything?

Maybe helpful, if I turn on the vibrato when it squeals, the squeal is vibrating just like the guitar signal - same for the reverb. That’s why I’m assuming the issue is in the pre amp area, maybe even before V2?
You are going to try changing the output transformer? Please get a second opinion.
 

HotBluePlates

Member
Messages
13,902
So I have a fairly new Fender Princeton Reverb Reissue ...

If it's "fairly new" then this should be a warranty-claim thing.

I would tend to look at the reverb, and ask if having the footswitch installed and turning off the reverb with the switch kills the noise when it happens.

However, anything more than padding the reverb tank more (if that even turns out to be the problem) would probably be invasive enough to void your warranty. And if you're right that it's not a microphonic preamp tube, the solution will probably be beyond the scope of an average player.

I'd suggest sending it in for repair, with detailed information on the conditions when the amp does/doesn't act up.

... I also have another output transformer for a Princeton that I would try if nothing else helps. ...
You are going to try changing the output transformer? Please get a second opinion.

It's almost certainly not an output transformer problem. The tremolo is applied to the signal path before the output transformer, and so tends to eliminate the transformer as a problem (apart from the fact a "bad output transformer" is almost never the problem in a malfunctioning amp).
 

fiveightandten

Silver Supporting Member
Messages
6,157
If the amp is new it should be under warranty. What you’re describing could be a HF oscillation. The only thing I might suggest that wouldn’t void your warranty is checking the lead dress in the amp. Sometimes OT leads or connectors between boards are placed in a very strategic location and the amp can be unstable if they’re not placed perfectly.

If you’re familiar with working inside a tube amp, it will be obvious to you what leads could pose a problem and may be worth playing with. If you’re not familiar with that stuff, leave it to a tech and get the work done under your warranty.

Outside of a lead issue, messing with anything else is likely to void your warranty, so I’d recommend against it unless you want to forego the warranty.
 

keliway

Member
Messages
3
Thanks a lot for all the replies!

Sounds like a microphonic tube - power tubes can be microphonic as well. Could be a microphonic component but that tends to be a bit on the rare side.
I see if I can get my hands on some Powertubes, thanks!

I had something like that on a new PRRI and it was not tube based but was a function of the reverb when set to high. Did the bench thing but it was never really solved and did not want to spend money replacing everything non tube. Best of luck.

If it's "fairly new" then this should be a warranty-claim thing.

I would tend to look at the reverb, and ask if having the footswitch installed and turning off the reverb with the switch kills the noise when it happens.

The squeal also appears with reverb turned off with the switch. I recorded a short video so you can hear it as well. I used an attenuator so not kill my ears but the issue appears without the attenuator as well.


If you’re familiar with working inside a tube amp, it will be obvious to you what leads could pose a problem and may be worth playing with. If you’re not familiar with that stuff, leave it to a tech and get the work done under your warranty.

I'm not an expert for sure, I installed new OTs, new pots and jacks (not in this amp) but nothing besides that. Would it help to post a picture of the insides?
 

gldtp99

Member
Messages
4,341
It's almost certainly not an output transformer problem. The tremolo is applied to the signal path before the output transformer, and so tends to eliminate the transformer as a problem (apart from the fact a "bad output transformer" is almost never the problem in a malfunctioning amp).

This.

Agree 100%.
 

keliway

Member
Messages
3
So well.. something strange just happened. I was already mentally preparing myself to be without an amp for the next 6 weeks and maybe as an act of frustration I opened up the amp one last time to see if my untrained eyes can spot something bad in there (idk, a mouse that was squealing because of my terrible playing?). I turned the amp on, terrible squealing. I touched some stuff (cables) with a chopstick, squealing doesn't even change. I turn the amp off, touched some more stuff with a chopstick, like the blue wire from the v2 socket that looks like the isolation on the solder joint is a bit off, turn it back on and well there is no squealing anymore.
So I guess I can open an amp tech shop now?

Jokes aside, wtf? I really don't now if this was related to the said cable, but even if it was, isn't V2 only for reverb and the squeal also appeared with reverb off? Anyways the cable doesnt look fine at the solder joint:

ikmGGJ9.jpg


So, what would you recommend doing now? Send the Amp back and wait 6 weeks telling them I can see a poorly isolated cable in there? Do nothing at all because now it works? Fix it by my own by resoldering or just put a tip of hotglue on the joint just like all the other wires have (i found another picture of an PRRI PCB and they have hotglue all over the cables)?
 
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HotBluePlates

Member
Messages
13,902
Sounds like a microphonic tube - power tubes can be microphonic as well. ...
... I see if I can get my hands on some Powertubes, thanks! ...

Microphonic power tubes (and rectifiers) generally have a metallic rattling sound, like the snares on the bottom of a snare drum, or brushes on the top of a snare drum.

Anyway, your follow-on test appears to prove this isn't power-tube-related:
... I turn the amp off, touched some more stuff with a chopstick, like the blue wire from the v2 socket ... turn it back on and well there is no squealing anymore. ...

... I really don't now if this was related to the said cable, but even if it was, isn't V2 only for reverb and the squeal also appeared with reverb off? ...

So, what would you recommend doing now? ...

You said, "touched some more stuff like the blue wire ..." So at this point, no one knows what was moved and why the squeal stopped.

However, let me point out a few things I see from the photo & video:

- There is popping when the volume control is turned that you didn't mention before, along with the extremely high-pitched squeal.

- The Volume control sits between the halves of V1, so its influence on the squeal is important.

- The Blue Wire you mentioned is after the 2nd half of V1, and is the Plate (output) for V2. This wire also connects (ultimately) to the Reverb Transformer and part of the power supply.

- In your photo, this Blue wire is laying on a Green Wire that runs to Pin 7 (grid input) of the 2nd half of V1, which is the same thing to which the Volume control connects. You have the output of a later stage possibly able to couple into the input of an earlier stage. And signals at V2 plate would be in-phase with V1 Pin 7, increasing the risk of oscillation.
So did you fix it? Possibly... But oscillation can also be at a frequency higher than human hearing so you might have only moved the frequency from ~14kHz (taking a guess at that very-high squeal) to something like 30kHz. Or maybe you killed it entirely by putting enough physical space between the wires.

At this point, unless you're gonna tackle this thing with an oscilloscope, you don't really know that you fixed anything, or if the problem is gone now & will come back later. You can try to move all V2 wires as far from V1 wiring as possible, then listen to hear what you get. There's an outside chance of bad power supply caps contributing to the issue (but that can't be known without also watching the squeal on a scope).

- The ragged appearance of the Blue wire for V2 isn't great but probably isn't a factor. Stripping/re-soldering it properly will require you to remove every front panel knob/jack/pot and then rotating the p.c. board up & toward the back panel to gain access to the solder pads. Do you really want to do this?
It's up to you how much you want to dig into this. If you do anything (visible), you'll wind up voiding your warranty and paying for any future bench time out-of-pocket. And without access to a scope (or at least a frequency counter), you won't really know the problem has stopped rather than continuing unobserved.

... I'm not an expert for sure, I installed new OTs, new pots and jacks (not in this amp) but nothing besides that. Would it help to post a picture of the insides?

If you have a higher-end DMM, you might have a frequency-counter function on it, which could help confirm the presence of the same high frequency at V2's output and V1 Pin 7. You could try to observe the a.c. volts reading at V1 Pin 7 to see it drop to a minimum when moving the V2 Blue wire, but it will be harder to discern noise vs squeal with a meter than with a scope.
 

zygoat

Silver Supporting Member
Messages
1,155
I'm having similar issues, not exactly the same as yours but I'll share. I've been cranking my PRRI more than normal now that I have an Ox Box. One day, with the volume on around 5 or 6 and a distortion pedal in front, mine started squealing too.. followed by the sound completely cutting out and a burning electronics smell. Pulled the chassis out and found a cooked choke resistor (R58). Had it replaced, complete re-tube with Tung Sols.

A few weeks later, same volume settings with a distortion box in front, the sound cuts out but this time with no squealing. Took a peek at the power tubes and they were flashing in and out with one going completely dark. Keep in mind these tubes had only a few hours on them.

So I'm really just frustrated at this point. I heard maybe Tung Sol 6V6s can't take beatings over time and that JJs may be a better option. So I'm waiting for my new tubes to show up and we'll see what happens. Really a shame, I love this amp.
 

Omi79

Member
Messages
255
See if the power tube retainers can be loose and if the are press them more together and try to change places for the two power tubes. If the V1 tube is microphonic it squeals as well tap it with a pencil and check
 

Mickey Shane

apolitical
Silver Supporting Member
Messages
3,028
So well.. something strange just happened. I was already mentally preparing myself to be without an amp for the next 6 weeks and maybe as an act of frustration I opened up the amp one last time to see if my untrained eyes can spot something bad in there (idk, a mouse that was squealing because of my terrible playing?). I turned the amp on, terrible squealing. I touched some stuff (cables) with a chopstick, squealing doesn't even change. I turn the amp off, touched some more stuff with a chopstick, like the blue wire from the v2 socket that looks like the isolation on the solder joint is a bit off, turn it back on and well there is no squealing anymore.
So I guess I can open an amp tech shop now?

Jokes aside, wtf? I really don't now if this was related to the said cable, but even if it was, isn't V2 only for reverb and the squeal also appeared with reverb off? Anyways the cable doesnt look fine at the solder joint:

ikmGGJ9.jpg


So, what would you recommend doing now? Send the Amp back and wait 6 weeks telling them I can see a poorly isolated cable in there? Do nothing at all because now it works? Fix it by my own by resoldering or just put a tip of hotglue on the joint just like all the other wires have (i found another picture of an PRRI PCB and they have hotglue all over the cables)?
I doubt that the "hot glue" or wax was originally designed into the circuit. More than likely, they had oscillation squeal problems while testing in R&D. and this is their band-aid. I'd stand the yellow wire up and give those three a good covering of whatever that stuff is because it's the easiest to try first.
 

HotBluePlates

Member
Messages
13,902
I doubt that the "hot glue" or wax was originally designed into the circuit. More than likely, they had oscillation squeal problems while testing in R&D. and this is their band-aid. ...

I think hot glue/silicone is ugly in all amps, but the purpose is less cynical that you're suggesting.

It's there to keep the wires from moving back & forth, because that would cause the wire to break right at the hole through the board.

Other amp companies that slather silicone on capacitors do so because the caps have significant mass, and could cause strain on their leads ultimately causing cracks/breakage of those leads or their solder joints.

I'm having similar issues, not exactly the same as yours but I'll share. I've been cranking my PRRI more than normal now that I have an Ox Box. One day, with the volume on around 5 or 6 and a distortion pedal in front, mine started squealing too.. followed by the sound completely cutting out and a burning electronics smell. Pulled the chassis out and found a cooked choke resistor (R58). Had it replaced, complete re-tube with Tung Sols.

A few weeks later, same volume settings with a distortion box in front, the sound cuts out but this time with no squealing. Took a peek at the power tubes and they were flashing in and out with one going completely dark. ...

Your amp might be oscillating due to the Ox Box's reactive load reflecting differently than an actual speaker. Again, you'd need to have a tech use a scope to monitor the amp while hooked up to your Ox Box.

Guys, you need to start looking at this stuff like surgery: you'd probably want the surgeon to know for sure what's wrong with you before they start cutting you open to take stuff out. A lot of amp malfunctions can have different causes, yet apparently-similar symptoms. That's why you pay a tech to find out what's actually wrong & fix it.
 




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