Rebel 20 tone change during warm up?

  • Thread starter Thread starter jwdubois
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jwdubois

jwdubois

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Tube amp newby question:

After I play my Rebel for an hour or so I seem to notice a very distinct and sometimes sudden tonal change that at a minimum requires some tweaking of the tone knobs. This normally takes the form of loss of treble. Sometimes, like last night, the change was abrupt and dramatic enough that I just quit playing, as cranking up the treble with the tone knob made it sound harsh.

I know that I should expect some tonal changes as the amp warms up, I'm just not sure how much I should expect. Would it make sense in my case to allow the amp a half hour or so warm up before I start playing?

As a tech question, are the tonal changes related to the tubes warming up and changing characteristics, or related to temperature coefficient changes in the passive components such as the tone stack R's and C's? Or both?

Another distinct possibility is that ear and brain fatigue are part the problem, but I'm not playing very loudly, and I don't seem to notice any significant changes in the tone of my backing tracks ....

:confused:

JWW
 
Well, FWIW, I let it warm up for about 45 minutes last night before I played. I was only able to play for an hour, but I did not notice the tone change. I'll try this a few more times (with and without the long warmup) to try to nullify the placebo effect.

JWW
 
Of course that would not be normal. Please be sure it is not something else in your chain. If you don't resolve it, please contact nate@egnateramps.com. Try one thing please if you haven't already. Try to verify if it does it with the TUBEMIX knob all the way to either pair of tubes. In other words, verify it does it with the knob all the way to the EL84 and also with the inob all the way to the 6V6. Report back...

Thanks
Bruce Egnater
 
That's weird. Don't have that problem with mine. A couple minutes and everything's fine.
Bruce, thanks for designing such a great amp. I just bought a second 112 cab for it and now it's exactly what I've always wanted in an amp. Sounds incredible.
 
Thanks for the reply Bruce. I've got some more experimentation to do. I regularly sweep the tube mix. I don't notice that either side drops off more than the other.

I asked the question to see whether anyone else notices this. Since no one else seems to, I think the Rebel is in the clear. It's just as likely that the treble drop I am hearing is just ear fatigue.

JWW
 
You would have to be playing fairly loud to cause that much of a tone change. Are you playing very loud when it does it....... or does it do it even at low volume? The Rebel is not "in the clear" yet.
 
I don't play loud in the the same sense that you get in a band situation, but my music room is pretty small and I'm very close to the speakers. It might be louder in dB than I think it is, but I don't think the Rebel is actually pushing any watts to speak of.

For perspective, I'm talking about starting out with the treble on the Rebel at ~9 oclock and ending up with the treble ~12 oclock.

The only way I can think of to objectively determine whether it's my gear or my ears would be to do some recordings, then compare the results with a spectrum analyzer. I don't think it matters all that much ;)

JWW
 
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