JCM 800 gets overly compressed and flubby....???

[bmwfreq]

Sorry, should have read the first post more closely. What happens when you turn the Post PIMV all the way up, taking it out of the circuit? Try using just the pre PIMV that the amp was designed with. Does it still get flubby after 30 minutes?

Yep. Still flubby even with the PPIMV out of the equation. Not to mention that I've tried many different PPIMV dual pot and safety resistor setups. So, I'm confident that this issue has nothing to do with the PPIMV mod.

But good question.

At this point I have a feeling that the filter can that the choke and screens are directly connected to is bad. I do have a few extra filter cans that I can replace it with until my new filter cans get here on Saturday. Just to see if this remedies the issue. I have a sneaking feeling that this is the issue. Fingers crossed that I'm right.

 

[Chris-in-LA]

Yep. Still flubby even with the PPIMV out of the equation. Not to mention that I've tried many different PPIMV dual pot and safety resistor setups. So, I'm confident that this issue has nothing to do with the PPIMV mod.

But good question.

At this point I have a feeling that the filter can that the choke and screens are directly connected to is bad. I do have a few extra filter cans that I can replace it with until my new filter cans get here on Saturday. Just to see if this remedies the issue. I have a sneaking feeling that this is the issue. Fingers crossed that I'm right.

You might be able to use jumpers to test your theory without removing the old one.

 

[bmwfreq]

I believe I have found and replaced the culprit (indicated with a yellow arrow.)

The second filter cap on the screens and choke measured...Yellow - 25M ohms/56.1uF, Red - OPEN/55.8uF.

So, I replaced this filter can with an extra F&T 50/50 that I had on hand, and the amp has sounded as expected for over 2 hours now. Whereas before the amp wouldn't last more than 20 minutes before becoming overly compressed and flubby.

At this point I can only guess that the amp will sound even better after replacing all of the filter caps after they arrive on Saturday.

Thank you to everyone that took the time to offer their opinions and suggestions. Much appreciated.