I suspect low line voltage is the cause.
Many SS amps, especially the small heads, will suffer from weak power lines. Your guitarist is right, but not using the right words. The linear power supply in a tube amp has a big power transformer and heavy capacitors that provide some power storage; this supply is very forgiving of power sags. (It's also where 50% of the weight and size are!)
At a gig, you have no idea if the venue has refrigerators or other equipment on the same circuit.
Bring a cheap line-tester and maybe a cheap voltmeter, and you'll know when you're getting insufficient line voltage.
Larger avatar photo here.
My usual stock answers: No, Tuesday, 12
Last edited by Rick Auricchio : 12-31-2009 at 11:47 AM.