65' Pro Reverb Popping, Crackling

[Hobart]

Hello,

I'm getting an intermittent loud crackling and popping sound from my 65' Pro Reverb (aa165). The noise is typically made worse by heavy strumming, but again, it is very intermittent and does not always come with heavy strumming. I've tried changing out the preamp tubes, cleaning the chassis components and I searched for cold solder joints, but found none. One thing I did find was a burnt section on the metal grating at the top of the cabinet, above the power transformer. Is it possible that the wires coming from the top of the transformer are arcing through their cloth insulation? Would this cause a popping, and crackling sound? I've also heard that old carbon comp. 100k plate resistors could attribute to this issue, but have yet to replace them. Thanks for the suggestions.

[xtian]

Sounds like you've done some good troubleshooting. Plate resistors are a likely cause. I find it pretty easy to replace them in a fender so I'd say go ahead. Just keep the originals in case you want to put them back.

[jelle]

+1!

[Hobart]

Thanks for the quick responses folks, I'll order up a set a give them a shot.

Any thoughts about the arcing hypothesis? Maybe I could carefully lay some mesh wire on the chassis and watch for arcing.

[jelle]

Maybe I could carefully lay some mesh wire on the chassis and watch for arcing.

NO. Please don't.

Please replace the 100k plate resistors with carbon film or metal film and report back.

[Hobart]

Is there any benefit to sticking with carbon comp?

[xtian]

Is there any benefit to sticking with carbon comp?

Only if you want to stay "original". Carbon (or metal) film are better for noise, especially at plate resistors where there's lots of current thru the resistors. I like CF.

[jelle]

Yes, noise.

[Hobart]

Thanks guys, I'll let you know how it goes.

[mhartman]

I had an old fender with loud popping recently, it turned out that the rectifier socket connections needed to be re-flowed. Works out great now. I have to admit, it took me a bit too long to track down. It was frustrating.

[Hobart]

Hey guys,

So I replaced the plate resistors, and the noise has so far seemed to be remedied. Now, however, there is an intermittent "bonnnnggg" sound, for lack of a better term. It's a humming type noise that only last for a second. It usually happens when I take the amp off of standby, although it has happened several times during normal operation. Thanks again.

[martin manning]

Have the power supply filter caps been replaced?

[Hobart]

Yes, I replaced them before the 100k's. As far as I can tell I wasn't experiencing this noise.