[Amps] Hi-pot testing

[KD7JYK DM09]

"Just sitting there, it started making an arcing noise (sort of) and 
showed plate current jumping around. "

New here, so mostly lurking, but this brought back memories of many 
issues over the years.  Have you checked for dust?  I've run into this 
many times, especially in TV's, and video displays, my experience with 
tube amps is limited, although I have a few.  Hyper-fine dust sticking 
to things, and causing tracking, and eventually arcing.  I took apart a 
hallicrafters TV to show to a friend (assuming the issue would exist), 
and there it was around the high voltage rectifier tube, fine dust, with 
some blackened areas due to corona.

One of the very first things I do when inspecting, is gently blow out, 
or vacuum any dust, and if possible, wash parts, boards, frames, cases, 
connectors, et cetera before applying power, especially with high 
voltage circuits.

Depending on the component, I use 91% rubbing alcohol, or QD Electric 
Contact Cleaner, then let dry very thoroughly.  Sometimes I use a small, 
soft nylon bristled brush to scrub away really tenacious crud.

Kurt