Source for SS schematics (Marshall AVT50)

[trem]

I replaced the input jack on a friends ValveState 2000 AVT50. I noticed R58 was very black, so I replaced it with a 1 watt 10 ohm. Now the amp wants to feed back pretty bad. With the gain at 9:00 and the volume on 12:00 it will feed back rather quickly.
I do not have much experience with SS amps, so a schematic might be helpful.
Thank You

[Enzo]

AVT50.

[trem]

Thank You

[trem]

Well, my friend picked up his amp and was very happy with it. He says it feeds back less now that it did before I "fixed" it. I am still not convinced that his amp is 100%. But then again this is a SS amp with what I would call A Lot of gain. More gain than I am use to hearing from Tube amps with post-PIMV. So maybe the amp does run as designed, and I am just very unfamiliar with that type of circuit/gain structure/amp. Like I say, my friend is happy as can be.

[ub2]

Thank You

[unparalleled]

Well, my friend picked up his amp and was very happy with it. He says it feeds back less now that it did before I "fixed" it. I am still not convinced that his amp is 100%. But then again this is a SS amp with what I would call A Lot of gain. More gain than I am use to hearing from Tube amps with post-PIMV. So maybe the amp does run as designed, and I am just very unfamiliar with that type of circuit/gain structure/amp. Like I say, my friend is happy as can be.

I had an AVT50 with the same problem, was totally unstable.
The amp was just out of warranty and had been sent back for repair twice for the same problems.
After trying everything to repair the amp I eventually replaced the Marshall power amp PCB assembly with an off the shelf kit with similar specs and a decent finned heatsink.
All the nasty distortion and HF oscillation dissapeared.
I am convinced that this particular model has an inherent design fault, the output chip has less external support components than the manufacturer's recommend to make the original device used stable.
Don't be surprised if your friend's amp fails again.