Rocknrollampsinc
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HI
I have a JCM900 reverb head on the bench again. It has brand new JJ Ecaps, brand new Mojo output transformer, brand new matched quad of JJ 6L6 output tubes and new preamp tubes.
The amp works fine, it does not blow fuses. However, when chunking hard on low bar chords there is a very noticeable crackling/unnatural distortion going on, alomost like an arcing sound. Master more than half way up, gain more than half way up.
I have tried the following:
1- retested all the new tubes, they test good
2-removed and replaced each tube one at a time- same problem
3- isolated the head from vibration - same problem
4- tried many different speaker cabinets and cables - same problem
5- visual inspection of the output tubes under stress shows nothing unusual
6- tried different guitars and cables - same problem
7- disconnected reverb pan, turned reverb off- same problem
Anyone have any ideas???
Thanks in advance
Jack

I have a JCM900 reverb head on the bench again. It has brand new JJ Ecaps, brand new Mojo output transformer, brand new matched quad of JJ 6L6 output tubes and new preamp tubes.
The amp works fine, it does not blow fuses. However, when chunking hard on low bar chords there is a very noticeable crackling/unnatural distortion going on, alomost like an arcing sound. Master more than half way up, gain more than half way up.
I have tried the following:
1- retested all the new tubes, they test good
2-removed and replaced each tube one at a time- same problem
3- isolated the head from vibration - same problem
4- tried many different speaker cabinets and cables - same problem
5- visual inspection of the output tubes under stress shows nothing unusual
6- tried different guitars and cables - same problem
7- disconnected reverb pan, turned reverb off- same problem
Anyone have any ideas???
Thanks in advance
Jack
