SF Twin Reverb with buzzy reverb

[1WoodHippie]

I've got a SF Twin Master Volume (non-push pull model). Vibrato channel sounds good but when you turn up the Reverb you get a buzzy/trashy distortion that seems to ride your signal. (ie. as your signal dies, so does buzz).

So far I've replaced the filter caps (needed it anyway), tried a known good pan/cables, swapped v3 and v4 tubes, tried a different reverb tranny, replaced all the components around V3, and the plate resistors on V1, v2 and v3, cleaned the pots and jacks and V3 tube socket.

It's driving me crazy.

Any suggestions?

thanks in advance!

[pdf64]

How about V4 plate resistors / socket retension? V4 section A is reverb recovery, section B is the dry/wet mixer.
Another contender is parasitic oscillation; tacking in some grid stoppers at the tube bases and checking for improvement can help track it down.
Pete