Hi all - I have a Peavey Classic 50 and it sounds AMAZING with my MXR 10 band EQ and Distortion+. HOWEVER, after about an hour of playing the clean channel starts to distort a little (not a harsh/f-ked speaker cone type of distortion, but it sounds like I am running an overdrive pedal through it).

I am an electronics noob so excuse my ignorance - but is this normal considering this is how bands in the 60s discovered distortion (by driving their tube amps), or is this peculiar, especially considering that this only starts to happen after the tubes have been warming for an hour?

Could it be a preamp tube issue? Would putting a 12AT7 in V1 help by dropping the gain?

Much appreciated.
It is not normal... 'Pushing the tubes' just means putting more input into the front, not running the amp for longer durations.

My guess would be it's a preamp tube going bad, as that's generally a fair guess for these types of issues... But I must admit it's odd that it'd take that long to become problematic each time.

Yes, putting a 12AT7 in V1 would lower the gain, but it may not address the actual issue. My first step would be swapping all the preamp tubes out, one at a time, after the issue has already started occurring. This could be problematic to troubleshoot. though, since it only happens after a while.

Try to narrow down as much as you can about the circumstances it does and doesn't happen under... Every little detail can help to track down the fault.
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