Bad case of ghosting...I've tried everything.

[bmwfreq]

To begin with. Thanks to everyone that replies. Everyone's input is most appreciated.

So, out of the blue and with no warning signs. My amp, a 1984 horizontal input JCM 800 2203 exhibits a bad case of ghosting. It's not as bad on the lower strings as it is on the G string on up. I also cannot turn the MV past 8 without the amp going into a low frequency feedback (like a kind of low rumble.) With the PA on 1, and the MV on 2, the amp should be nice and clean. It is not. I have a mild distortion with these low settings when I shouldn't.

I have done the following to remedy the issue, but to absolutely no avail:
New 50uF/50uF filter caps x 5
New 10uF 100v bias caps x2
New resistors everywhere - entire PCB
New PRE-AMP tubes
New power tubes
all new coupling caps -5x.022uF/2x.1uF/1x.68uF
all new pots
Tried different speaker cords, instrument cords, guitars, speaker cabs, power cables, wall outlets
Addressed lead dress till I'm blue in the face
Changed the balancing resistors on the screen filters from 56K to 220K and even 470K (even tried NO resistors)
Checked for bad solder joints and reflowed solder almost everywhere
Change the OT (40-18026)
Tried a different choke
Even tried some alternate grounding schemes

None of these changes made any difference in my ghosting or feedback issue. Needless to say...I'm at a total loss at this point.

Any suggestions with the exception of the things I've already tried would be greatly appreciated.

[xtian]

Welcome to TAG. You didn't mention whether you tested (or replaced) the 1K/5W screen resistors and 5K5 grid resistors, which are normally socket-mounted.

[romberg]

Do your power tubes have grid stoppers? My '82 2204 came from the factory without any. If they are not
there on your amp you might try adding some.

It has to be something simple as you have almost rebuilt the entire amp .

Mike

[Stevem]

You did not mention if you tried different known good preamp tubes.

I have had a condition like that a few times that was due to a preamp tube.

Have you tried a different speaker?

[pdf64]

I suggest cleaning up all connections to the chassis. One or more of those lugs etc may have developed corrosion etc, preventing a good connection.

[cdemike]

Since ghosting is a power supply issue and the amp seems to have been essentially rebuilt (except for the PT, which I think is likely fine), I'd want to know how everything measures in the amp currently. Are you getting any AC current anywhere without anything plugged in? All B+ and cathode voltages look right? Is bias stable? Do voltages at the tube socket pins measure correctly?

It seems to me that you've ruled out old power supply capacitors, tubes (maybe try shuffling preamp tubes between positions?), grounding, bad wall mains supply, guitar issues, cables, etc. So I think it makes the most sense to look for empirical clues with those measurements to narrow down the search.