Mesa Subway Rocket Issue...maybe

[Pryde]

Hello Folks

Wanted to get your thoughts on this Mesa I have. The owner claims the amp sounds great and then becomes "thin" sounding after say an hour of playing. That is the only descriptor he gives, no other issues, pops, crackles, hum, etc.

So I ran the amp for over an hour, monitored preamp and power tube voltages and everything remained stable with no change in sound at all (still sounds really good).

I hate to give it back and say nothing is wrong or just recommend new tubes when it appears the current ones are ok. The only issue is the power tubes are biased hot (EL84 fixed bias) at 32 m/a but there is no red plating or even excessive heat after an hour of loud playing.

Also I checked all pots for the notorious loose back plate issue and all are solid/tight.

So what you seasoned pros do at this point?
Thanks for the advice.

schematic links for Mesa Subway Rocket:
Schematics: Mesa Boogie: Index : Updated June 7, 2012

[Chuck H]

Ask about the rest of his gear. Perhaps a low battery in a preamp or effect? It could be that his ears simply acclimate with time and "just turned on" amp seems bigger sounding than once his ears acclimate to the volume. Then he can hear how small it is. You've pretty much taken the amp out of the equation.

[g1]

Ask about the rest of his gear.

For sure. As it's not always the most comfortable thing to do, I have to wonder iif you were running it for an hour through the speaker.

[Pryde]

For sure. As it's not always the most comfortable thing to do, I have to wonder iif you were running it for an hour through the speaker.

Yes I left the amp on the entire time (not switched to standby at all) with guitar plugged in and played it every 10 minutes or so and re-checked voltages then as well. No decrease in volume or girth from what I could detect.