Static on a fender twin PI

[Curranproducer]

OK, I recapped and modded a silverface 75 twin to blackface spec's. re-tubed and biased, BUT there is a static noise in the amp now. I used my scope to locate the noise, and it is in the PI. it is in the front of the caps and after the caps(.1uf) it is also on the tube plates. it is no where before that in the circuit. I have re-flowed the solder on the connections and also run new wire in some spots around the PI tube. I also swapped out the PI tube. does this sound like I need to swap out the caps and resistors in this section of the amp again?

[matt h]

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[Gaz]

I 2nd the PI plate resistors as prime suspect since you already tried swapping the tube.

[Curranproducer]

whoosy crackles, it is before and after BOTH of the .1uf caps after the PI Plates. so static coming off of the PI Plates going into the caps fefore the 220k's going into the power tubes.

[matt h]

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[jjman]

Check the PS node that feeds those plate resistors and also all the cathode resistor area.

[Curranproducer]

the only spot where the crackle whoosh come in is on the plates of the PI. the other pins are clean of any noise

[matt h]

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[Stevem]

Replace the two plate load resistors and replace them with 1 metal film types for the least noise, in fact with this amps age I would replace all the plate load resistors in the but for the ones in the tremolo section!

[Blindog]

The other thing that's possible, if this has one of those fishpaper boards, is that the board has gone conductive. You might want to probe the board to see if there's some stray DC in that area. (it's a quick and easy check)

Yes, check this...I have a '68 Traynor YBA-1 that had that type of board. I rebuilt it to plexi specs, and it developed a weird blocking distortion problem in the PI...tried everything, didn't go away until I rebuilt the circuit on a Garolite board.

Mark

[Curranproducer]

I disconnected the tremolo circuit to use the tube for a merlin FX loop.

[Curranproducer]

I disconnected the tremolo circuit to use the tube for a merlin FX loop.

[Curranproducer]

I was also wondering if there are any cool mods I can do for the reverb section of the amp? Are there any improvements that can be made to the circuit?

[gui_tarzan]

Replace the two plate load resistors and replace them with 1 metal film types for the least noise, in fact with this amps age I would replace all the plate load resistors in the but for the ones in the tremolo section!

This ^

Don't forget about the 100K resistors in the pre-amp section. Almost every old Fender I've worked on has needed these replaced to get rid of static sounds.

[Curranproducer]

do you mean the 100k' that feed the plates on all the preamp tubes?