5150 II effects loop noise

Hi I was wondering if anyone could help me... I have a 5150 II and I run an MXR 10 band eq through the effects loop. I've been doing that for about 5 years and its worked fine. Now, when I put the loop on, it makes a high pitched whine, static, and the signal doesn't go through all that well. Then It goes away after awhile and comes back when I turn on the amp again. I've checked the cables, tubes, used contact cleaner in the eq, amp jacks (send / return) and checked the footswtich... none of these are the problem. If anyone knows what the problem might be or have had a similar problem I'd appreciate your help. Thanks.

Sounds like microphonic noise in a preamp tube. I know you mentioned you checked the tubes, but check the preamp tubes again. Also, I don't know much about the MXR EQ, but try running the volume slider a smidgen under the 0 level...like halfway between that and the -8 and use the post volume on the head to compensate.


bud i recently had the same prob with my 5150mk2 with an mxr 10band. I did my own testing with the pencil (tapping the tubes) and what not and found nothing. Took it to my tech and one of the tube holders or something like that in the preamp section had malfunctioned/broke and it needed replacing as well as the tube.

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im guessing your the original thread maker right?



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