Grainy reverb problem

[bluesguitar]

I'm getting a grainy lingering sustain, even a seeming increase in signal at the end of notes in my reverb on my '76 Princeton Reverb amp. Does this symptom ring a bell with anyone? Also would it be safe to swap my reverb tank from my Tweed Blues Jr to see if the problem is the reverb tank?

[Structo]

Do you have a 12AT7 in V3?

[bluesguitar]

I have a 12ax7 in V3.

[Roe]

have you tried a 12at7/ecc81/cv4024?

[bluesguitar]

The tube chart calls for an ax7. I'll try a different ax7 tube to see if the problem may be the tube. I have capacitors on order for a cap job, since this has never been done. I'll retire the amp for safety until then. Thanks

[Roe]

The tube chart calls for an ax7. I'll try a different ax7 tube to see if the problem may be the tube. I have capacitors on order for a cap job, since this has never been done. I'll retire the amp for safety until then. Thanks

strange. the reverb driver should be a 12at7. Cf. http://www.thevintagesound.com/ffg/prin ... rb_sf.html

[bluesguitar]

I agree. That is strange indeed. My tube chart shows from left to right, 5u4gb, 6v6, 6v6, 12ax7, 12ax7, 12at7, 7025. I'll research it some more.

[bluesguitar]

After a bit of research I found a website that concures with my tube chart. At the top of the article it shows the tube locations and their functions. Unfortunately in the article itself they sometimes refer to V3 as the reverb driver. So, it can be confusing. At least it concures with my tube chart and I can rest at ease knowing my tubes are in their correct locations. http://fenderguru.com/amps/princeton-reverb

[rdjones]

After a bit of research I found a website that concures with my tube chart. At the top of the article it shows the tube locations and their functions. Unfortunately in the article itself they sometimes refer to V3 as the reverb driver. So, it can be confusing. At least it concures with my tube chart and I can rest at ease knowing my tubes are in their correct locations. http://fenderguru.com/amps/princeton-reverb

http://www.electronicstudio.net/schemat ... _schem.pdf

V2 is 12AT7, reverb driver
V3B is 12AX7, reverb recovery and

You can try to sub the tank, but the Blues series reverb is a different impedance and will sound different, lower and may not reveal much.

Can you visibly inspect the springs and check for excessive looseness ?

reddog Steve

[bluesguitar]

I'm glad you mentioned the spring tension. I had suspicions about that since sometimes just the vibration from walking across the floor, or moving the amp slightly would cause reverb spring noise.

[Structo]

Carefully check the transducer mounts inside the box.

These can be damaged or break from physical shock, like dropping or rough handling.

[bluesguitar]

I took the tank out and inspected it. Left all connections intact. The springs seem to have plenty of tension and are connected well. No drooping that I thought may have been a problem. Put it back in and fired the amp up. Absolutely no hint of the grainy distortion. So, unfortunately all I know at this point is that it is one of those most frustrating intermittent issues. Would have liked to have determined the cause for the benefit of others who may be curious. I'm not banking on the problem being solved, so will update with any new developments.

[Firestorm]

The ground connection to the reverb tank is contact only (not soldered) so it might go intermittant. And the RCA jacks do get corroded with time. So by taking it apart and putting it back, you may have cleaned things up. You might have been hearing dirty connections.

[rdjones]

I took the tank out and inspected it. Left all connections intact. The springs seem to have plenty of tension and are connected well. No drooping that I thought may have been a problem. Put it back in and fired the amp up. Absolutely no hint of the grainy distortion. So, unfortunately all I know at this point is that it is one of those most frustrating intermittent issues. Would have liked to have determined the cause for the benefit of others who may be curious. I'm not banking on the problem being solved, so will update with any new developments.

One of the weirdest reverb problems I've found was a spider had made a web in one of the transducers.

rd

[marshamps]

grainy distortion on PRs is somewhat common. It's caused by grid conduction to the cathode. worse in PRs than other blackface amps because of the under board crossover lead dress. Fixes are a 150K grid stopper on the Reverb Driver 12AT7 (V2) and a 330pf from plate to cathode of the rev. driver. This makes all Fender reverbs sound warmer and a touch thicker as well!!!! IMHO.
Have fun,