This is my late 90s red Fender Prosonic, which I purchased non-functional for pretty cheap - had a blown speaker, some bad tubes, missing the back panel, etc, but after I addressed those things and replaced the filter caps, I was able to get it up and running… for awhile anyway.
Then it developed a weird issue. After running for a while and getting warm, it would start to make this horrendous crackling, static sound that was not affected by the volume control, and persisted even with nothing plugged in. Sometimes the noise would stop if I pulled some tubes and then reinstalled them - always gone when I pulled the phase inverter (V6), so I knew it was in the preamp somewhere - or if I put it in standby for a bit and and then back into play mode, the noise would quit temporarily. It was VERY intermittent, and sometimes the noise would just stop on its own, even when the amp was hot after running for hours. I couldn’t *make* it happen, but I could guarantee that it would present sooner or later… which basically made the amp unusably unreliable.
The problem turned out to be the 150pf silver mica cap between the plate of V2a and the treble control, which was intermittently leaking DC voltage. In the video, I demonstrate the issue and explain how I fixed the problem. I hope someone out there who loves these amps as much as I do finds this helpful, as there seems to be almost nothing on YouTube showing the inside of Prosonic amps or any servicing, much less anything specific about this problem.
![](https://i.ytimg.com/vi/EXgk1fnBSD4/maxresdefault.jpg)