Mark IV - losing volume on occasion

[badguitarist]

Hi guys. Yesterday I replaced Class A tubes (initially Mesa 6L6 STR430) of my Mark IV to an used pair of STR440. I also swapped V1 and V3 with JJ's 12AX7's (initially stock Mesa 12AX7's). I played for quite a long time without any problems. But today the volume reduced gradually for about half a minute or so and finally there were pretty much no sounds but then it gradually increased back. That happened twice and I had no idea why. Can anyone shed me some light please?

 

[ANIMATED SUSPENSION]

That's usually a sign of dying power tubes. Buying used power tubes is very risky, you don't know how they've been abused or how many hours use they've had.

 

[badguitarist]

That's usually a sign of dying power tubes. Buying used power tubes is very risky, you don't know how they've been abused or how many hours use they've had.

Thanks mate for the answer. That's so true. This was my first time buying 2nd hand tubes. Will never do that again!