Bad Tubes in Preamp?
 

Is there any way to know that a tube is bad without a tube checker? The output of my Mesa Boogie Triaxis pramp begins to fade in and out after playing for 10-15 minutes. Does this sound like a tube? According to the manual, the tubes perform the following functions:

V1 = Lead 1 input
V2 = Input for all other modes
V3 = Lead and Rhythm mixer
V4 = Lead 2
V5 = Effects return stage

It does it across all of the modes so it seems that either more than one tube failed at the same time or either the Lead and Rhythm mixer or Effect return tube may be bad. I assume this since V3 and V5 appear to be the only tubes that are shared by all modes. I turned off the effects loop with the front switch on the Triaxis and it had no effect. Is this pointing to the V3 tube?

Any help would be appreciated.

Richard

Re: Bad Tubes in Preamp?
 

have no idea. but how lond has it been since you've changed the tubes? how many hours are on them? maybe it's time to change them anyway.

Re: Bad Tubes in Preamp?
 

POhysical inspection usually can indicate a bad tube. they should all have a nice blue glow. If any are glowing yellowis or orange, that is the reuslt of al leak in the seal (oxygen burning), and the tube should be replaced.

Otherwise replace each tube one at a time, and then in pairs. If you solve the problem, ou found the bad tube.

Hope this is helpful.

Re: Bad Tubes in Preamp?
 

Pre amp tubes don't glow blue like power tubes, and they last for years. they might become micophonic and you can usually tell just by tapping on them with a pencil while your pre amp is on. wiggling them around a bit might expose a loose tube socket connection...

you problem doesent seem like a bad tube. seems more like a capacitor or loose solder joint.

Re: Bad Tubes in Preamp?
 

over 90% of your problems with tube amps or PREAMPS ARE TUBE RELATED.Try switching some around or just go get a new set .I would get the mesa ones though.I just did this in my mesa studio preamp and it worked.Seriously move the tubes in new spots and see if that temporarily helps.This is easy on the triaxis cause the tubes are accesible.

Re: Bad Tubes in Preamp?
 

Thanks for all of the advice. But, it turns out the solution was a lot easier. I grabbed a Volt/Ohm meter and began checking cables in my rack. Three of them tested bad!!! I replaced them and now it sounds perfect.

Richard