Tube failure?

[cellardweller]

My Solo 50 was making a sound I guess to be the infamous "motorboating" sound of tube failure, during practice.
I grabbed my standby's, replaced the power tubes and this seems to have remedied it.

I would describe the sound as a faint and quiet "thud thud thud....thud...thud thud....thud-thud-thud" at random intervals and speeds, but constant once the amp was on for a while.

As I said, I replaced the power tubes, and it appears to have fixed it, but practice was over and I didn't leave the amp on for very long after....

Does what I have described sound like tube failure?
If so, pre-amp or power tube?
I have not replaced any pre-tubes yet....

 

[rusman75089]

it sounds like the power tubes to me. if you hear microphonics while playing and then you replace the power tubes and it went away, it sounds like that was it. one way to tell is to tap the power tubes while it is on. if you hear a bass sound without struming, that is most likely it.

 

[cscotto]

Motorboating, which is the sound you describe, could be either a problem in the power supply or a pre-amp or power tube gone bad. I had the exact same problem in my Nomad. It turned out to be the Sovtek LPS I had in the PI position. Changed the tube, problem gone.

 

[blazer986]

With the replacement power tubes fixing the issue, I would leave it at that - bad power tubes. Unless the noise comes back or the amp is having other issue sounds like problemo solved .

 

[cellardweller]

With the replacement power tubes fixing the issue, I would leave it at that - bad power tubes. Unless the noise comes back or the amp is having other issue sounds like problemo solved .

Yeah, I hope so.
Will find out tomorrow. :?

 

[cellardweller]

About an hour into playing, it began again with a vengeance.
I changed out V1 through V5, and it seems to have solved the problem.

Hopefully this means the old JJ 6L6's are still good to keep around as spares!

It took some tweaking, but I think I like the sound of the old Mesa stock tubes better than the JJ's...or it may have just been relief that it was in fact only a tube that had gone bad!

 

[cellardweller]

Does the intermittent behavior suggest anything or rule anything out?

We haven't practiced again, and that seems to be the only time the amp is pushed hard enough to do it.....