Well, I can't remember the plate voltage of the Framus amps, but you calculate it based on that. What I would do is take a reading of where it's at now, then plug in the new tubes, and try to match that. Actually, did you buy it new? It might be biased cold from the factory. If you have absolutely NO idea what you're doing, it might be advisable to take it to a tech, no matter how much you loathe doing that.
To bias properly, you would need to find the plate voltage, and without a bias probe, what you have to do is remove the amp from the shell, turn it on, and have it upside down, so have it suspended between like 2 bricks or something
Plug it into a load (your cab), turn it on, don't plug a guitar into it, then measure the voltage across pin 3 (I think) and ground. That will tell you plate voltage. Then you calculate your optimum bias from that.
This dude will set you straight.
I'm no tech...so definitely double check everything I'm saying
I've biased my own shit just because I'm stupid and I don't give a fuck. I actually shocked myself like REALLY bad doing my Carvin TS100. My arm went numb for a day, my vision blacked out for like a second, etc. That could have been a lot worse probably