tube rec. for Joule- Electra VZN 100 amps

Great amps. I would keep the tubes you have. As far as I know, they are not made anymore and they were made by one manufacturer in Russia. 

bopper,

The VZN-100 uses the Russian 6C33 output tube. They are generally pretty sturdy and good sounding tubes (especially as used in the Joule OTL amps! IMO) ... actually I find ones with some good hours on them sound better than fresh/new ones. As long as the bias up well in the amp - they are good to go. There is no other substitute for this tubes. There are plenty of them still around though (event if they have not been made in years).

The front end tubes are 6922/6DJ8, 5751, and 6350. Those should be all labeled.

Rich Brkich
Signature Sound