[Amps] Weird tubes in an amplifier

[Mark]

Just when I thought I had heard of almost every type of tube in an amplifier, I talked to a ham that has 2 VT4C's in an older home brew amplifier he has for sale. It's a really big amplifier. He thinks it puts out about 500 watts. I've never heard of this tube before. Is it worth getting anything this big for 500 watts? Can anything be substituted in place of these tubes? Its running 866's for rectification. I haven't seen it yet but may drive an hour to go take a look. Thanks for any feedback you guys might have on this tube. Appreciate it..

73
Mark
W0NCL