I have a home brew 4-1000. About 10 years ago when I started testing, I plugged in a $1.00 hamfest tube I bought to use for a lamp base. The filament lit when voltage was applied, so I applied HV then drive and got RF out... nearly 75% of a good tube I finially replaced it with. I don't know if it was a 4-1000 or 3-1000, but it worked. It's hard to kill one. Bob