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Marshall JCM 900 100W, Need Voltages!


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6/10/2003 1:19 AM
superdave
Marshall JCM 900 100W, Need Voltages!
A buddy of mine asked me to take a look at his 1990 JCM 900 head. Apparently it has too low of a volume response (the gain channel is super low until about 4 on the pot) and the clean channel is exhibiting a ring modulator (slight) type noise on top of notes and chords. Not the best sound. I checked the bias it was high. I set it according to the schem in the weber book. SOunds better but...I told him I'd be glad to change the power tubes and filter caps as they're the original and seem like an obvious place to start, however I need voltages for the schem so I can check and see if anything is out of whack on any of the tubes (indicating bad coupling caps, grid resistors, etc. I mainly deal with vintage fenders and plexis so this circuit board stuff is a little out of my realm, but the basics is the basics, eh. If anyone has any clues or some voltages let me know, Thanks!
 
6/15/2003 3:36 AM
Richie

You should be able to find the voltages on the schematics.. just lookup the model number.  
 
http://www.marshallschematics.com/  
 
Richie
 

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