#1
Hi all. I just tried to change the tubes in my Mesa Mark IV from EL34s back to 6l6s. I put in the new tubes, turned the amp on, and when I took it off standbye it makes this terrible humming noise through the speaker. So I switch back to the tubes I used before, but now the amp won't even turn on, not even the fan. One thing I did notice: one of the new tubes didn't have that central bit that all the pins surround, but instead it had what is best described as a nipple of sorts; do you guys think that made any difference? Somebody please tell me it's not dead.
#2
Check the fuse?
Call me Wes.
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#3
Doesn't sound reassuring.

Post it to me, it may as well be bin fodder...

=]

On a serious note, no idea. Doesn't an amp need biasing for different types of tubes?

And it may well be just a fuse.
#4
^No, Mark IVs have a fixed bias and can take EL34s in the outer two sockets, which is what I was doing before.
#5
Definately change the fuse(s) before anything else. If that fails it could be an OT gone or something so then it would be best to take it to a tech.
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#6
Fixed bias is definitely a wrong choice of words that amp makers have used. Fixed bias actually means the bias can and does need to be adjusted.There are a lot of great articles on biasing out there. Take a look.
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