[Amps] Help with Henry 2K-2

[John Simmons]

My workhorse Henry is broken, alas! I'm looking for suggestions.

The amp has been used almost daily for the last year. One morning I 
turned it on and was listening to a net, so the amp was unkeyed and 
warmed up. I heard an arc, so I shut the amp off. A thorough inspection 
was conducted. The plate fuse (on the back of the amp) was blown and 
black. All of the power supply components check OK. There are no shorts 
in the tubes. There is no evidence of arc-over anywhere that I can find. 
Neither the amp manual nor the Internet has been of any help.

I'm waiting for the plate fuses that I ordered to be delivered. Any 
ideas of where to look for the cause?

73,
-John NI0K