KT88 monoblock loss of gain - signal or drive tube issue? Or something else?

[Psilonaught]

I've just spent several hours trying to debug why i was getting a difference in gain between my speakers with my new crossover. It appears after everything, and presumably by coincidence, that the issue isn't with the dac, pre or crossover but with one of my tube amps. Swapping them out for my bass amps sorts the problem.

So now I need to find the cause of the drop in gain. It isn't dead, it powers up, and doesn't distort, but it has about 50% of the gain of the other one.

The amp has 12AU7 signals and KT88 drivers.

Before I start pulling tubes what is likely to be the issue?

 

[TECUMSEH VALLEY]

If it is a valve issue, then I would suggest swapping over the pair of 12AU7 tubes in the monoblocks and see what transpires.

 

[Psilonaught]

If it is a valve issue, then I would suggest swapping over the pair of 12AU7 tubes in the monoblocks and see what transpires.

Ok thanks.

 

[Psilonaught]

yep, signal tubes were faulty.

What an extraordinary example of sod's law in action. I swap crossovers at the point where a tube decides to go. I proceed to waste my entire Sunday pulling out cables and my hair....

At least it isn't the actual crossover, and the tubes are in warranty from Hotrox hopefully since they are about 2 months old, so but sheesh, what a ball ache!

I'm surprised at the reliability of Psvane, they are Art series tubes and were very expensive!