Garbly hissy noise on startup Princeton reverb

[schmee]

Starting a new thread on this issue as it was buried in a thread on another problem.
'71 Princeton Reverb

Synopsis:
What would do this in the reverb circuit? When a note is played the first time after the amp is turned on, the amp goes nuts with loud garbly hiss/crackle unaffected by volume control turned off. It stops entirely when you rotate the Reverb potentiometer up and down.

From the other day: "Suddenly today it started making a crackly garbly noise and fairly loud. (started with the first note of playing after the amp warmed up)
-Volume control didn't change that sound at all.... even off.
-I dimed the reverb, it got louder... then the noise quit entirely when I rolled back to 7-8.
- Played quite a bit more and loudly and no issues at all. "

It did this again last night at rehearsal, I rotated the Reverb knob and it quit..... was fine then for 3 hours after.

So I suspect something is going on in the Reverb circuit. Both reverb send and recovery tubes were changed yesterday.. For the T7 I put a NOS Sylvania Mil Spec in. For the recovery AX7 I put in a known proper working tube. So I doubt it's anything to do with those tubes, the amp did the same thing before and after.
The RCA cables ends were cleaned while I had the chassis out.

Just looking for hints of most likely candidates. I'll have to get the chassis out again to measure voltages on the reverb send and recovery tubes. What in the Reverb circuit would be effected, eliminating noise/problem by rotating/cycling the pot?

 

[Peegoo]

@schmee Check the ground on the reverb control pot. Remove the knob and nut and washer. If you see any corrosion, scrub it off. Make sure it's snug when you reassemble.

Reseat the reverb tubes. Matter of fact, reseat all tubes while you're in there. When you pull each tube, give the tube pins a blast of CRC or Deoxit and stick it back in while still wet. Don't shoot the stuff into the sockets.

 

[schmee]

@schmee Check the ground on the reverb control pot. Remove the knob and nut and washer. If you see any corrosion, scrub it off. Make sure it's snug when you reassemble.

Reseat the reverb tubes. Matter of fact, reseat all tubes while you're in there. When you pull each tube, give the tube pins a blast of CRC or Deoxit and stick it back in while still wet. Don't shoot the stuff into the sockets.

I just reseated the tubes yesterday and cleaned the sockets to attempt to rectify this.
I had this amp front panel apart maybe 6 months ago, there's no corrosion etc and it's clean, but will check that pot grounding for looseness etc.

Have you had an issue shooting into the sockets? I do that all the time. I found these things on Amazon making cleaning 9 pin sockets a lot easier, they come in a pack with 4 different brush sizes for next to nuttin:

 

[Jasonpatrick]

Did you slightly bend a pin and it’s now going behind the socket pin clamp? That happens. Causes all sorts of noise when gain is added. Also, I’ve never had an issues spraying the socket? Why would you not shoot the socket with deoxit? Lol

 

[Jasonpatrick]

To add to above, , I bent the pin on V1 of my deluxe reverb and it would make all sorts of noises and then stop. Fixed it when I realized it was going behind the pin holder clip thing and not in the center.

 

[Strat Jacket]

As an aside...
When you re-seat the tubes, either use nitrile gloves or wipe them with isopropyl (the glass part) after touching with bare fingers. The oils from your skin will accelerate failure.

 

[Peegoo]

I just reseated the tubes yesterday and cleaned the sockets to attempt to rectify this.
I had this amp front panel apart maybe 6 months ago, there's no corrosion etc and it's clean, but will check that pot grounding for looseness etc.

Have you had an issue shooting into the sockets? I do that all the time. I found these things on Amazon making cleaning 9 pin sockets a lot easier, they come in a pack with 4 different brush sizes for next to nuttin:

View attachment 1076832

I don't squirt cleaner into chasses simply as a matter of practice. Now if I have it opened up and put a wad of paper towel behind the socket, absolutely I'll blast the socket itself.

^^^That is a nice brush. I've been using airbrush cleaning brushes for years when doing amp maintenance. There are several sizes on a little ring, and they are perfect for scrubbing tube sockets.

For 1/4" jacks, there's nothing better than a .25-cal brass/bronze bore brush. I glue 'em into a short section of 1/2" or 3/8" dowel. Jam it in, rotate it twice, pull it out. Done.

 

[schmee]

To add to above, , I bent the pin on V1 of my deluxe reverb and it would make all sorts of noises and then stop. Fixed it when I realized it was going behind the pin holder clip thing and not in the center.

They looked good. Once, years ago, I bent a pin almost 90 degrees and it was laying across the socket!

 

[Peegoo]

As an aside...
When you re-seat the tubes, either use nitrile gloves or wipe them with isopropyl (the glass part) after touching with bare fingers. The oils from your skin will accelerate failure.

This belief came from the problem of oils on halogen bulbs--where it does matter--because the clear envelopes are made of quartz.

Vacuum tubes use borosilicate glass envelopes and don't get that hot; they are more like a standard light bulb. There's no risk because the glass does not get hot enough to create hot spots as occurs on quartz halogen bulbs.

 

[Strat Jacket]

This belief came from the problem of oils on halogen bulbs--where it does matter--because the clear envelopes are made of quartz.

Vacuum tubes use borosilicate glass envelopes and don't get that hot; they are more like a standard light bulb. There's no risk because the glass does not get hot enough to create hot spots as occurs on quartz halogen bulbs.

Looks like I stand corrected! I'll probably still do it (alcohol wipe), though...can't hurt anything.

 

[corliss1]

Why would you not shoot the socket with deoxit?

Because you don't want to lubricate the tube pins. Deoxit, at least the formulation used for pots, isn't the appropriate cleaner for tube sockets. Use a non-lubricating contact cleaner sparingly in that location.

 

[Peegoo]

Looks like I stand corrected! I'll probably still do it (alcohol wipe), though...can't hurt anything.

Absolutely it is good practice to keep everything clean when it comes to electronics.

 

[RLM69]

Schmee,
This: It stops entirely when you rotate the Reverb potentiometer up and down.
What I gather from this, and I may be wrong, is the reverb pot is going bad. Possibly part of the carbon trace is worn out. I would put a VOM meter on it while rotating it and you should be able to tell. Good Luck.

 

[loudboy]

I have a '78 SFPR that crackles on startup. I smack it on the top a few times and it stops.

 

[schmee]

Schmee,
This: It stops entirely when you rotate the Reverb potentiometer up and down.
What I gather from this, and I may be wrong, is the reverb pot is going bad. Possibly part of the carbon trace is worn out. I would put a VOM meter on it while rotating it and you should be able to tell. Good Luck.

Yeah, I was thinking of that this am, but it seems like there isn't really dead spots. But I'm going to check it out! Thanks.

 

[dan40]

Have you checked any of the components in the reverb circuit yet? Are the small bypass caps on the cathodes of the driver and recovery tube original?

 

[schmee]

Have you checked any of the components in the reverb circuit yet? Are the small bypass caps on the cathodes of the driver and recovery tube original?

I turned the amp on yesterday, playing a bit ...the gnarly sound started. The Reverb was on 3, turning it off the noise went away. I unplugged the reverb cables, but after a minute or two low level crackling started, not too loud, more of a "hiss crackle". This sounds like a tube, driver or recovery, but I have already put a couple in to see.

If you mean the little 25v/25uf electrolytics no, they aren't very old. It seems this has got to be in the reverb circuit somewhere though.

Here's a question:
-Will components in the Reverb circuit make noise even if the tank is unplugged?
-How about if the Reverb is set to 0 but no switch being used? (I better test it with a switch I guess)

 

[slider313]

I would reflow the solder connections to the reverb pot.

 

[panacea]

Try a different tube in the reverb section

 

[schmee]

Latest:
Today I went out to play it. Yesterday I had unplugged the reverb tank cables. I connected them today and played for probably an hour or 45 minutes. No noises whatsoever. UGH. I hate intermittant issues.

But hopefully, it was dirty RCA sockets and when I removed and reinstalled the cables things got OK. Fingers crossed....

Still would like to know:
-Will components in the Reverb circuit make an amp noise even if the tank is unplugged? (tubes, caps etc)
-If the Reverb is set to 0 but no switch being used (So not turned off, just dialed off) Will a defect in the reverb circuit still cause amp noises?
@Wally @Peegoo @corliss1 @John Backlund