VOX AC30/6 TB scratchy static noise

[Telebuckers]

Hey guys- I've got an AC30 here that works fine on the normal channel, but when you turn up the vib/trem volume or the brilliant channel volume there is a really loud scratchy static-y kind of noise coming out relentlessly. I tried remelting a lot of the solder joints and tried new tubes and all that good stuff- any other things I should look for?

Schem-
http://www.schematicheaven.com/voxamps/ac3093pr.pdf (pre)
http://www.schematicheaven.com/voxamps/ac3093pa.pdf (power)

[bluesfreak]

How old is the amp? Could be time for a cap replacement.
Also check if you can see any kinds of arcing the Rectifier Tube or on any Tube sockets related to the Brilliant channel.

[Telebuckers]

Amp's not that old, in the 5 to 10 year old range probably. What I'm a little confused about is that by looking at the schematic it looks like the normal and brilliant channels share a circuit, so why am I not getting the noise on the normal channel as well, but getting it on the trem and brilliant channels?

[bluesfreak]

Not completely, the Brilliant utilizes 1/2 of a V1b in addition to the normal channel. However, all do share one thing, the Input Jacks. If they corrode and do not short properly to ground when not used you might have strange noises.. hope that just cleaning the jacks will cure your amp....

[pdf64]

The 33uF/350V B+ caps on the vib (C30), and tone (C36), circuits could be tired, as bluesfreak suggested. Try tacking new caps across them to see if that helps.

[pecorporation]

Check R28, R29 & R32 around the input jacks. Verify that they are 1M ohm and not starting to drift off-spec.

[Telebuckers]

Well I cleaned the input jacks with some good ol deoxit, and checked the 1M resistors on the input jacks and they're all good. Also checked C36 and C38 and they both read pretty close to 33uf. I didn't try tacking new ones across them though. STill have the noise.

Now that I've checked further, the noise IS on the Normal channel, just A LOT quieter. On the Brilliant channel you can hear the static but also the trem cycling in the background. I pulled v11- still noise. Pulled v10- still noise. Pulled v9- noise gone, but so is all the other signal.

[bluesfreak]

If you pull V9 and its gone it could be either V9 or somewhere in the Vib/Trem Channel but if I follow my intuition I would replace the Rectifier Tube first...
Anyway, best would be to get a Scope and follow the signal back to see where the spikes do come from. This might require breaking the circuit at certain points but this would then the quickest and most efficient way to track down the bugger...

[Telebuckers]

Ok thanks bluesfreak I'll try changing the rectifier and see what happens and go from there.

[Telebuckers]

Now that I think about it I already tried replacing the rectifier with the same result. Looks like it's gonna be tougher than that.