R
River City Studios
Member
Hey everybody,
Finally took some time off day job to work on a new project in my studio and I'm having amp problems. I have a 77 JMP 2203 that was modified by Rockstah. When playing certain low end notes (especially palm muted bar chords) the amp emits this crackling sound that I can best describe as the sound that bacon makes when you fry it in a pan. Here is the signal chain:
Les Paul -> Mogami guitar cable -> Marshall -> Mogami speaker cable -> Marshall 1960BX cab
I have completed the following trouble shooting:
-Tried 3 other guitars
-Tried 3 other guitar cables
-Tried 2 other speaker cables
-Tried another cab
-replaced the pre-amp and power tubes with 2 different sets that were known to be good
-Cleaned the tube sockets and pots with contact cleaner
-biased the amp
Problem still exists.
In reading other forums (Metroamp), someone mentioned that failing/failed screen grid resistors on the 12AX7 sockets could cause a crackling noise like I have described. Does this jive with anyone here? If so, is it possible to change these on my own without electrocuting myself?
Unfortunately, I live in an area that is deprived of quality amp techs. I've taken amps to the few that are available and they sent my "fixed" amps back without being fixed. I guess I could box it up and ship it to someone, but I'd rather avoid the expense, if possible. Any guidance would be appreciated.
Thanks in advance,
--Dan S.
Finally took some time off day job to work on a new project in my studio and I'm having amp problems. I have a 77 JMP 2203 that was modified by Rockstah. When playing certain low end notes (especially palm muted bar chords) the amp emits this crackling sound that I can best describe as the sound that bacon makes when you fry it in a pan. Here is the signal chain:
Les Paul -> Mogami guitar cable -> Marshall -> Mogami speaker cable -> Marshall 1960BX cab
I have completed the following trouble shooting:
-Tried 3 other guitars
-Tried 3 other guitar cables
-Tried 2 other speaker cables
-Tried another cab
-replaced the pre-amp and power tubes with 2 different sets that were known to be good
-Cleaned the tube sockets and pots with contact cleaner
-biased the amp
Problem still exists.
In reading other forums (Metroamp), someone mentioned that failing/failed screen grid resistors on the 12AX7 sockets could cause a crackling noise like I have described. Does this jive with anyone here? If so, is it possible to change these on my own without electrocuting myself?
Unfortunately, I live in an area that is deprived of quality amp techs. I've taken amps to the few that are available and they sent my "fixed" amps back without being fixed. I guess I could box it up and ship it to someone, but I'd rather avoid the expense, if possible. Any guidance would be appreciated.
Thanks in advance,
--Dan S.