JCM 900 problems arghh... valves??

the_knuckleduster · Newbie Alert Joined: 28 Jan 2007 Posts: 1

ok well ...

a couple of weeks back i am using my JCM 900 100w reissue with my Zoom GFX-4 plugged in in the effects box everythings working fine , i turn it off .... come back about 2 hours later and turn on again and now i am getting this un-utterable ringing coming from the amp , this has stopped since i have removed the pedal from the loop and am now plugging straight into the amp , which .. to begin with sounded fine but now i get feedback all the time and the sound is becoming crunchier and more muffled , now my first thoughts are oh oh a valves gone/going ...well they all look fine , and seeing as i have no idea what i am doing i have decided not to mess about with it ... i am wondering if it could be one of the pre-amp valves because it seems to sound more and more crackled the more i play with the bass etc etc ...

any ideas...
___________

owwdatune

waldo · Posted: Wed Jun 27, 2007 2:33 am Post subject:

Are all 4 tubes a nice orange glowing colour? (although you may still have an issue with them even if they do look ok.) If not then you might 'see' a bad main tube. The preamp tubes could also be the problem - in fact one of them is responsible for the fx-loop so your culprit might be there - but you will not see a colour change here.

test - swop the preamp tubes around to see if the fault goes away - of course one of the 2 channels will now have the fault but at least you will know more...

Cheers brett