2:90 hum on channel b

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RJ2213

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im using a triaxis v2 and a older 2:90. it seems that the 2:90 i recently purchased used is causing a hum from channel b. no matter what cables i use or what channel on the triaxis i use to feed the signal into the 2:90 channel A sounds fine but channel B has a hum. tried using the ground lift to no avail. tonight i'm going to try swapping the tubes around to see what happens.

anyone else have any ideas for this?
 
when the amp is in standby the hum stops, flip the standby and get ready to rock with a channel b that hums.
 
its most likely a tube then, as there really isnt anything complicated inside a 2:90, especially if its channel-specific. find out which tubes belong to which channel, and swap them around, then see if the hum is coming from channel A. if that happens, youve found the problem
 
http://forum.grailtone.com/viewtopic.php?t=14226

Here you can see the tubes ,channel B I think is the right one,swap them around as RAYDER said and maybe you'll be free of it. :wink:
 
Yes its the power tubes also preamp tubes can ad humI know Im late on this post SEE the post,, HUM in MESA STEREO 290 SOLVED that explains it.
 
2ninety12ax7.jpg
 
Ok thats wrong at least for my 2:90.. CHB is in the center and CHA is last left in photo.And with those Phase inverters Drivers the main thing is to have matched half's there are 2 circuits in each 12AX7'.. I have the Blue light 2:90 version.
 
I also have a blue pilot light version. I pulled each PI separately to see which channel would stop working when each tube is not in and that's what I found.
 

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