Sizzling Bacon sound Fender Princeton.

[devilsindetails]

While taking a break from my Gibson GA15-RVT tremolo circuit woes (see other thread) I decided to look at an issue that's recently cropped up on a Fender 6v6 based Princeton. (Besides Fender Amps are so much nicer to work on and troubleshoot) than those "%$&@% Gibsons"

Anyways...I re-tubed the Fender, upgraded the speaker to a Celestion Sp-10, cleaned the pots etc and detected a "crackling, sizzling bacon" sound emanating from the speaker. Only really noticeable when I max out volume.

I checked and cleaned the pins and sockets, ensured speaker connections were secure and checked for any loose chassis wiring...all seems fine.

I've heard that the old carbon comp resistors, while still reading on spec...can actually break down (the carbon granules or something like that) and introduce a sizzling or crackling bacon sound to the output.

I've heard that plate load resistors are often culprits. ANy other usual suspects that you fellows know of?

Thanks Leon

[tubeswell]

Did you try a tube swap? (One of your new tubes could be a dud)

(then check the CCs. Could be a bad plate resistor)

[Milkmansound]

often on old Fenders the circuit card flexes from exposure to ambient moisture in the air, and that causes hairline fractures in the carbon resistors mounted on the circuit card.

Its a pain to troubleshoot. If you hear crackling and spitting sounds while the amp is in idle - the plate load or cathode ground resistors in the preamp may be the culprit. I usually poke them with a chop stick and use freeze spray/heat gun to find them. Or you can just methodically shotgun until its gone.

Fender amps are my favorite - but I really despise those fiber boards.

[devilsindetails]

Did you try a tube swap? (One of your new tubes could be a dud)

(then check the CCs. Could be a bad plate resistor)

Yes, no change with tubeswap...turned out to be a bad plate resistor..thks for your help as usual tubeswell...still working on that damn Gibson trem problem...

[devilsindetails]

often on old Fenders the circuit card flexes from exposure to ambient moisture in the air, and that causes hairline fractures in the carbon resistors mounted on the circuit card.

Its a pain to troubleshoot. If you hear crackling and spitting sounds while the amp is in idle - the plate load or cathode ground resistors in the preamp may be the culprit. I usually poke them with a chop stick and use freeze spray/heat gun to find them. Or you can just methodically shotgun until its gone.

Fender amps are my favorite - but I really despise those fiber boards.

Turned out to be a plate resistor...but an excellent point about the Fender fiber boards...I have an old Super Reverb on the bench and that board looks like a roller coaster...I'm having nightmares just thinking about the grief its going to give me when I get to it...thanks for your help Milkmansound

[Firestorm]

I had a Fender in once where the board had warped so badly the PI ground pulled out of the solder. Still worked though, because the NFB circuit lets the PI ground through the speaker. Speaker eventually died from full-time DC.