Tone on my Genz-Benz Streamliner 900 seems to have changed...

Recently my amp is sounding very subdued in the treble/high end (sort of like it has a head cold). I find myself with the treble maxed on the bass and higher than normal on the head. I spent quite a bit of time with trying different settings on the amp and basses but still, the same result. Normally I don't touch the treble on the amp or bass (my active ones at least). I'm usually tweaking the mids if anything. However even the tone of the beefy mids that I love seems to be lacking. I'm wondering if the tubes are aging and losing ht the top end; but given I don't know much of anything about tubes, I could be way off here.
I did have to replace one back in September (completely different issue; much more drastic) and am now wondering if the others are due.

Thoughts?

Mark

Drums-Bass-Mallet Synth
More Info at:
www.m13productions.com

 

All better. Just replaced both v2 and v3 with Mesa tubes actually. It's now back to the amp I love
Thanks again.