Bias CAT JL2 + Tube swap 6550C = KT120

Hi all,
I just bought a second hand JL2 Signature MK2 (with the 6550C tubes).

In order to set it up correctly I need the following advice:

1) what should be the general bias of the 6550C tubes? In the manual it states 30, but I read in this forum that it should be 37, so I am confused...

2) And should the right value be 30, as the manual states, it is referred to new tubes. But my tubes are not new, so I imagine that I should bias at a lower level, right? How much lower? The tubes are 1 year old.

3) Once the bias is set, the value is not steady, but it moves (i.e. if I set 30 it goes randomly and continuously from 29 to 31 in a period of 5 seconds)

4) Is it correct that after setting the bias to 30 when the item is hot then when I turn it on the day after and it's cold it marks 38 and then after 1 hour it gets to 31-32?

5) Is it correct that after setting the balance to 0 when the amp is hot the the day after (when it's cold) it has a different value (say +2.00. And it stays to +2.00 also when it gets hot)? Should I continuosly correct it?

6) Also, every time I switch the amp on, the circuit breaker comes in and cut the energy. I have a 10A on a 230V line. Shouldn't it be enough?

7) FINALLY: would it be possible to swap the stock 6550C with the new KT120? Or there are other changes involved?

thanks to everybody.
It sounds as if your current tubes are not holding their bias well. I think the small flucation will allow the amp to play but the tubes are on there way out.
You have to ask Ken Stevens if the trandformers will supply the necesarry voltage to cope with the KT-120.
Finally something is definately wrong with the your power ratings for the receptacle you are using. Cab you get a higher current dedicated line . ( I am assuming you mean your house breaker not on the amp. If its the amp you need repairs)
They can take the KT120's, per my recent conversation with Ken. Not cheap. I think it should be 30, and that 29 to 31 is no problem. I don't know about biasing the tubes to zero. If you contact me - same user name on audiocircle, I can give you more information. Unfortunately you can't contact me directly here on agon.