Super Reverb Issue

[madmartigan]

Hi everyone! Hoping somebody can help me troubleahoot this thing.
The amp in question is a 65 blackface ab763 clone bought from Marsh, in kit form. The only things that veer away from the original circuit are a master volume and a 2/4/8ohm output tranny. I built this amp myself about 5 years ago and it has been runnin strong since, until recently....
Now, I can follow a schematic and layout, and build with the best of them, but as you know, troubleshooting is a whole other animal. So here is the problem. Im getting a horrible crackling sound thats almost pattern like, on the pick attack and the sustain. Ive narrowed it down to something in the reverb circuit (I think). Here are the things I've tried...
Unplugged the tank, sound is still there. Changed out v3 and v4 with known good tubes, still there. Removed v3 entirely, AHA! That stops it! I've replaced the 25/25 cap and 2.2k, and also tried a .002 cap across the reverb tranny secondary to combat parasitic oscillation as in a silver face schematic but neither of these helped. I have also reflowed everything in the vicinity.
Here is a vid of the problem:
http://youtu.be/MDZFZiWpFa8
If anyone can think of anything off the top of their heads please chime in. Sorry for the long winded post and thanks in advance!

[Blackburn]

Have you tried replacing V3 with a different tube?

[martin manning]

I'd suspect the reverb driver transformer or the screen filter cap.

[madmartigan]

Any way to test the transformer without replacing it?

[martin manning]

Unfortunately the problem may not be detectable with a low voltage test for shorted turns. Does the odd noise come through the reverb when the tank is connected? That might be an indication that the transformer is faulty.

[Firestorm]

I hate to recommend random parts replacement as a diagnostic tool, but these trannies are pretty cheap.

[madmartigan]

The static comes through whether the tank is connected or not. I was just messing with it and realized that it only happens on the vibrato channel. I plugged into the normal channel and it sounds fine. For some reason I thought it was both, my mistake.
Yeah on mojotone the tranny is only like 12 bucks. I was thinking about ordering one along with every component in the circuit but man what a pain that'll be. Then I'll find out it was something stupid like a dirty pot

[martin manning]

Well, it's not exactly random... we know that if the current flowing through the transformer's primary is stopped, the noise stops. What I was asking is if the noise is any different (has reverb) with the tank connected.

[Firestorm]

Well, it's not exactly random... we know that if the current flowing through the transformer's primary is stopped, the noise stops. What I was asking is if the noise is any different (has reverb) with the tank connected.

No, not really random. It seems to be the locale. But to rule one way or the other, the simplest thing would seem to be replacement of the $10 transformer.

[madmartigan]

Just plugged in the tank. Static is still there and reverb sounds great!

[Baddog01]

Did you check all input and output jacks to make sure they are still tight. Did you check all ground wires and ground points in the amp? Vibration can cause things to loosen up over the years.
Did you try the chop stick trick and try pocking around in the amp with it on the bench ?

Keith

[M Fowler]

To me it sounds like cold solder joint. Every thing on V3 pretty much goes to ground so I would check all solder joints on V3 tube socket and the grounding of those components.

The only other thing there is the reverb driver.

Mark