The aforementioned 4XEL84 circuit is located here:
http://www.arrakis.es/~igapop/20w4xel8.htm
It's in Russian, but can still be "decrypted". They don't give impedance
values for the OPT, but that can be easily figured out.
The site is in Spain, and has a lot of info on amps and circuits from all over the world. Have fun!
/ed brown in NH