I changed tube today and all is well :)
I started with measuring the bias on the old ones and Tube 2 was on 7,6 mV!
So, I took it out and found the following:
The glass of the tube is actually melted B)
Anyway, I still had some barely used JJ's and decides to give them a try.
I'm rehearsing tonight and can't wait to hear what they sound like!
I'll keep you posted.
P.s. Apparently I can't have the picture in the text without it also showing up under "attached thumbnails". A bit annoying <_<
talwilkins's post in Dt-25 Humming Loudly In Triode Mode was marked as the answer