component thermal drift?

[automattack]

I've got a Rev G two-channel Dual Rectifier (serial R-014701), recently re-capped, had both plate resistors and a grid stop replaced.

What I've noticed is the sound changes drastically over hours. When I first turn it on, it sounds kinda meh -not bad, but not great - even after letting it warm up 20 minutes or more. I tend to turn it on standby when I get to band practice, and let it warm up while we all catch up, tune, etc... At the end of three hours, it's totally different sounding, a lot warmers, less brittle.

Is component thermal drift a thing in these amps? Anything I should look for? or know?

 

[screamingdaisy]

Every Mesa I've owned has sounded better after about 20 minutes of playing (playing generates more heat than leaving it on standby).

It's a trade off. Some amps start off sounding good, then start to mush up after an hour or so.

 

[tele twister]

A long time ago...after playing for several hours in a hot crowded bar, my Dean Markley half stack had never, ever sounded so good...
...and then the dreaded puff of smoke rose from the head, and the scent of roasted transformer. Hmm.

But dang, it never sounded better than just before it happened

 

[afu]

I haven't looked into this, but it brings to mind the way particles react to heat. As they becomes warmer, the particles move more quickly and can even begin to "dance"; ice melts, water might boil, solid materials expand (and can melt, break, or combust). All other things being equal, it stands to reason that hot tubes are going to be drawing electrons at a higher rate, because they have more potential to move and a greater surface area through which to travel. I imagine that's why modern electronic data sheets often list a temperature next to performance stats.

 

[deeman]

It could be ear fatigue that makes you perceive that the tone is changing as you continue to play/listen.

Who knows.

 

[afu]

It could be ear fatigue that makes you perceive that the tone is changing as you continue to play/listen.

Who knows.

This!! Especially when I spend too much time 2 feet from the cab.

 

[domct203]

I've got a Rev G two-channel Dual Rectifier (serial R-014701), recently re-capped, had both plate resistors and a grid stop replaced.

What I've noticed is the sound changes drastically over hours. When I first turn it on, it sounds kinda meh -not bad, but not great - even after letting it warm up 20 minutes or more. I tend to turn it on standby when I get to band practice, and let it warm up while we all catch up, tune, etc... At the end of three hours, it's totally different sounding, a lot warmers, less brittle.

Is component thermal drift a thing in these amps? Anything I should look for? or know?

How did the amp perform before this service? Did you have the amp serviced to address these issues, or did the issues start after the service?

It could also simply be ear fatigue as mentioned. I know my ears ring after a two hour gig, even with Hearos.

Dom

 

[automattack]

I don't think it's my ears - I always wear ear plugs, and I don't perceive such drastic changes with any of my other amps.

Before the service, it did the same thing. The service was for another issue; once it got warmed up, it would start popping randomly.

Someone in another forum said they remembered something about a bad batch of PCBs and suggested I call Mesa. They couldn't find anything online about it though... Anyone hear about this?