Crap, while half asleep I was powering down my P-P 6550 amp which has seperate switches for filaments and the B+. I screwed up and turned off the filaments, but left on the B+ ALL NIGHT while I was asleep. In the quiet of morning, I could hear a very slight transformer hum. Inspecting the amp, I noticed the hum was the power transformer, as well as heat coming off the un lit tubes. after powering down, and then later turning it back on, everything seems OK....is this hard on the output transformers or output tubes?
Well there you go, I don’t believe that not preheating the filaments, before turning on the B+ causes undue harm at moderate voltages.
If the point is avoid "cathode stripping". One mistake like yours and you have subjected your tubes to more stripping voltage then they would see in many lifetimes of instant on use.
That said, I would check the bias and keep a close eye on them for a wile to make sure that say, the heater cathode insulation or something was not damaged.
Has there service life been reduced? Time will tell…John
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