That is where I obtained them - RAAF!! When the airforce went digital it dumped millions of dollars worth of stuff into auctions. That's where I get my valves from. I have both pentodes and triodes in that miniature format. The photo I posted is a 5718 triode.
I will do some work using some I think and post my results. It will be good to listen to my Hi-Fi at 60,000 feet too.
Joe