SF Twin Reverb with buzzy reverb

[BigE]

On the bench is a SF Twin Reverb with Master Volume.  (non-push pull model)  When you turn up the reverb you get a nasty buzzy/trashy sound on top of your signal.  Turn the reverb down/off and the regular signal sounds fine.  I noticed that when i didn't have any input plugged in i got a lot of trash/hiss/noise through the reverb just idling.  Pull out V3 or turn reverb down and the trash quits.

I've done a Filter cap job.  Tried a known good pan/cables.  Cleaned and retensioned V3 socket.  Tried different Tube.  Replaced all the parts around V3 and the output of the stage before.  Nothing seems to clean up the signal.  All the voltages look good.

Anybody got any suggestions?  It's driving me nuts!

thanks in advance.

[The_Gaz]

Is this a Twin with master volume/ Do you have a scope? If you do, try scoping the input and output of the reverb to see if you can isolate where the noise is coming from.

[eleventeen]

It may or may not fix the reverb issue, but I wouldn't be too surprised if it did. Those 100K plate resistors on most of the preamp tubes are a definite suspect if the thing is making rodent noises with nothing plugged in. The 3 watt metal film Doug sells are perfect. Just replace them all. You'll be stunned at the difference it makes.

[HotBluePlates]

I always got a lot of extra background hiss in the reverb circuit of my old '67 Super Reverb.

I didn't try it when I owned the amp, but what about moving the red wire of the reverb transformer to a lower-voltage filter cap? I think there's a wire running from the eyelet the red wire connects to back through the chassis and to the filter caps under the cap cover. In reality, it would be the end of this wire under the cover which you move, but will do the same thing as moving the red reverb transformer wire itself.

[BigE]

Thanks for the tips guys!

So I've swapped the plate resistors on V2 and V3.  Along with the .02 and 500p coupling caps.  Even tried a different reverb tranny.  The trash i had while it was idling is gone, but I still get a buzz when you turn the reverb up.  The buzz comes and goes as the signal comes and goes.  Not like a ground buzz but a subtle distortion-ish buzz.   Cleaned all the pots and jacks.  I scoped the signal going through V3 and it looked fine.

I'm at my wits end at this point.

Any suggestions?

[eleventeen]

Just some drive-by ideas: Have you scoped the output of the reverb can? And checked the quality of the grounding of same and the cables that feed & return the reverb signal? What is the signal you are feeding the amp? A sine wave gen? Measure the 1 Meg R on the grid of the 12AT7 driver tube; if that R is badly off, it could affect the amount of drive to that stage (long shot!) And finally, inside the reverb can, make sure the grounds are integral. I would start this by ohming the far end of the cables going to & coming from the rev can, measuring both the input resistance, which I believe should be pretty low and the output resistance which I think should be in the 2500 ohm range and whether the two grounds (the cable shields) are continuous. It's not uncommon to find the teeny wires inside the rev can distressed or broken. They often break at the RCA connectors. You could be getting some buzz if the grounding is weak. But...see if you can determine this without taking the rev can out and apart by measuring the far ends of the cables. The rev can, in most cases, be fixed by very carefully resoldering the tiny wires inside.