Looks like this tube would require a -/+ 19V grid drive in Class AB1, PP operation, with an 8K A-A OPT.
http://frank.pocnet.net/sheets/082/e/EL12N.pdfIt would be good idea to have some additional drive capability, in order to properly (cleanly) handle any brief peaks or transients.
It looks like they are using cathode bias (350 ohms per EL12N), fixed bias would be even better for power output and lower THD
For Class A Pentode single ended, VA = 250V, IA = 72 mA, I G2 = 11 mA, 3.5K OPT, RK = 90 ohms, R G1 = 30K, it would require +/- 7V rms drive.
/ed B