Transmitter tubes in guitar amps was an idea i had about 3 years ago with the tube in my avatar - GU81. The power efficiency on them is absolute junk but the lifespan is measured in years, not months. Average lifespan of a GU81 is 20 years at 80% capacity. I would also estimate the B+ to be around 800-1kV or so. The GU81 amp i began to design required on average 1.2kV at 20mA.
Interesting to know how they handle shock and transporting - thats where i ran into a snag. Also the chassis has to be very large to have physical distance of some parts of the amp due to arc-over. The 6550's on the right are used as drivers to drive the tube which is most likely a gigantic dual-envelop triode.
I messed in this ballgame for the longest time. I dropped out when i was having to design a transformer that could handle the job on a regular house 15A breaker.