Fender BG Hot Rod Deluxe noise issue

[threenofingers]

Thanks Mick, I'll track down some Deoxit

I had the back off today and there's no sign of heat damage around the CR13 & CR14 or R78 & 79, no visible leaks from the capacitors. Generally looks to be in great condition.

[Tom Phillips]

Thanks Mick, I'll track down some Deoxit...

The important point to keep in mind is that, for pots, you need to use a cleaner / deoxidizer that leaves a bit of lubricant behind after the cleaning is done. If you were to use an aggressive cleaner that washes out the small amount of lubricant in the pot, the pot may initially perform better. However, after some time it will be in distress and could seize up.

[threenofingers]

Sounds like the pots might just need cleaning?

Any particular reason the pots ONLY play up in the "more drive" channel and not the clean and the drive channels?

[g1]

Any particular reason the pots ONLY play up in the "more drive" channel and not the clean and the drive channels?

No, that is a good point and rules out the pots if they are always good in the other channels. I missed that earlier.

[g1]

The only thing the 'more drive' seems to do is engage the cathode bypass capacitors for the 2 halves of V2, boosting gain of V2 stages.
That means in 'more drive' mode, you are much more likely to have issues with microphonic preamp tube in V2 position.
Try swapping V2 and V3 around and see if it makes a difference.

[threenofingers]

looking at the schematic, does the V2 link to the treble, bass & middle pots? Bearing mind it's affecting the drive pot as well

[g1]

Try it. It's a very simple tube swap. Microphonic tubes are a very common cause of issues like yours.
Because it's a type of feedback, cause and effect can be tricky. Like maybe it's not affecting the drive pot, the drive pot is affecting it.
The t,m,b pots are right before the V2 stages, so they may affect it as well.

[threenofingers]

Try it. It's a very simple tube swap. Microphonic tubes are a very common cause of issues like yours.
Because it's a type of feedback, cause and effect can be tricky. Like maybe it's not affecting the drive pot, the drive pot is affecting it.
The t,m,b pots are right before the V2 stages, so they may affect it as well.

Awesome, cheers...

[threenofingers]

I removed the V2 tube & the noise stopped, then I changed the V2 Tube (12ax7) with a similar tube ( ECC 83) but the issues haven't changed. I'm assuming it's not the tubes. I guess it's off to the pro's.

[threenofingers]

The only thing the 'more drive' seems to do is engage the cathode bypass capacitors for the 2 halves of V2, boosting gain of V2 stages.
That means in 'more drive' mode, you are much more likely to have issues with microphonic preamp tube in V2 position.
Try swapping V2 and V3 around and see if it makes a difference.

Swapped these tubes over .... no change

[nosaj]

I'll be honest one of the 1st things I do when i get a HRD on the bench is solder reflow the ribbon cables and the tubes.
nosaj