Members LedZep1985 Posted February 14, 2008 Members Share Posted February 14, 2008 I just put two new Tung Sol 12AX7 pre-amp tubes in my Marshall JCM 900 4500 head earlier today. I tried it out, and it sounds so much better now, but when I was done playing and put the amp on standby, the amp was making some crackling sounds. This hasn't happened before to this amp. Can the new pre amp tubes be casuing this? I also would like to know what should I use to clean the inside of the head? The amp has collected a bit of dust inside, and I'm not sure what to use that'll be safe for the amp. Link to comment Share on other sites More sharing options...
Members LedZep1985 Posted March 4, 2008 Author Members Share Posted March 4, 2008 I just tried it again today, and it was making the crackling noises even when the amp was still on standby. I took it off standby, and I played for about a minute, and there was a big "pop" sound to it, and even when bringing the volume up to 10, it was very low in volume. What has happened to the amp? How much should repairs cost around? Link to comment Share on other sites More sharing options...
Members Duesentrieb Posted March 4, 2008 Members Share Posted March 4, 2008 1) swap old tubes back into it2) put a patch cable into the loop result? Link to comment Share on other sites More sharing options...
Members la0tsu Posted March 4, 2008 Members Share Posted March 4, 2008 If that doesn't work, try removing the rice krispies. Link to comment Share on other sites More sharing options...
Members mseriously30 Posted March 4, 2008 Members Share Posted March 4, 2008 If that doesn't work, try removing the rice krispies. Or at the very least, wrap them in tin foil or saran wrap. Link to comment Share on other sites More sharing options...
Members JonathanD Posted March 4, 2008 Members Share Posted March 4, 2008 Listen to Olaf. He knows things. Link to comment Share on other sites More sharing options...
Members Matt300ZXT Posted March 4, 2008 Members Share Posted March 4, 2008 To clean the chassis on my amps, I just use q-tips and rubbing alcohol. That'll get the dirt and caked on dust off. For cleaning circuits, I use quick dry contact cleaner. Make sure it's unplugged of course and be sure to let it dry completely before you power it back up. I'd also spray some cleaner on the pins of all the tubes and install/uninstall them 3 or 4 times to clean out the sockets really well. Also, take a guitar cable and spray it with the cleaner and plug it in and out of the jack a few times too. That's about all the preventitive maintenance you can do. Otherwise, take it to a local amp tech and have him check out the caps. It's common for caps to go out, especially on older amps like the 900s. Link to comment Share on other sites More sharing options...
Members LedZep1985 Posted March 16, 2008 Author Members Share Posted March 16, 2008 I brought the 900 to a reputable amp tech last week, and he just called me back letting me know what was wrong with the amp. The output transformer was the problem, which took out some of the wattage of the amp. He recommended changing the output transformer to a JCM 800 50w transformer, because they sound and work much better than the JCM 900 output transformers. Also, he did a modification at my request to try to get the eq to have more of a Plexi tone to it. I can't wait to pick it up, and plug it into my 4x12 loaded with Greenbacks. Link to comment Share on other sites More sharing options...
Members knucklefux Posted March 16, 2008 Members Share Posted March 16, 2008 don't worry...that noise is just the suck trying to get out. it never will, but it will continue to try. Link to comment Share on other sites More sharing options...
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