Another Bad Tube?

[4406cuda]

A couple of weeks back, all the modes in channel three were barely audible. It turned out to be a bad tube in the V3 socket.

Now, when ever I switch to the Mark IV mode I hear a high pitch frequency oscillating. It is only audible in the Mark IV mode and does not go away with the volume turned down on the guitar. I tried 3 different guitars and the high frequency oscillation was still there, even when the cable was not connected to the input jack on the amp.

Is it a bad tube? Why does it only affect the Mark IV mode? If it is a bad tube, what tube is it likely to be?

 

[Anonymous]

If you have time and spare tubes.. try first of all a new preamp tube in V3. If that doesn't work, take a look at the manual on page 62 for tube replacement...

you said that the problem only happens on mark iv, base on that i would try replacing V1, V3, V4, V5 and V6 by an eliminating process (replace one tube at the time eg. replace V1 with a new tube. if that didn't fix your problem, put back the stock V1 and go to the next tube etc.)

you probably know this but just in case: any time you replace tubes take the new tube in and out the socket 2 or 3 times, this will create a good contact!!!!!!!

If you are not comfortable with this take it back to your dealer.

Good luck :wink:

 

[#2121313]

This sounds like the problem I had, but it happened in all modes in CH3, mine turned about to be a bad pre amp tube in V1. Yours, because it happens only in the MKIV mode might be due to a different tube (V2, 3 etc ???). I'm not sure, I would suggest trying the V1 tube anyway.

It sounds like one of the pre amp tubes are microphonic causing the noise you hear...I wouldn't be concerned at this point until you check all tubes...

Good luck, let us know what happens.

 

[4406cuda]

I will try your suggestions, just got to pick up a new JJ 12AX7.

Thanks

 

[#2121313]

BTW, your dealer should be able to replace the tube under warranty, Mesa offers a 6 month warranty on tubes, I actually called Mesa and they are sending me one directly, but if you gotta go out and buy one (cause you don't have a spare) get your dealer to replace the defective one under warranty.