You want to check it at least every month if you wish to continue to claim benefits as victim of audio nervosa.
The nice thing is the more you check it, the more you realize how screwed up it is, and the worse your nervosa becomes. Also, the better biased the amp, the nicer it sounds and the more addicted to screwed up tube amps you become. It's spiritual path, enlightenment through joy and suffering with tubes.
Here's a nice article on bias.
http://www.aikenamps.com/Biasing.htmlDespite the marketing hype about more power and more internal cooling, your tubes can dissipate 25W like any other el34, at least that's the spec.
http://www.groovetubes.com/assets/1690_gt_ts0107final_e34ls.pdfI have looked but I can't find the output tube plate voltage for your amp. If you can find that out, then you can determine at what bias current gives 70% max dissipation for class AB operation. That would be your max, but burns tubes fastest.
My snappers sounded great running right at 17.5W (70%) dissipation with those same tubes. But they had 575V plate, highest I've seen in a el34 hifi amp. Tubes lasted 2000 hours running like that. (~11 months for me).
