SVT CL preamp tubes

[vit]

Hi everybody!
Here's Vittorio from Italy, I'm new to the forum and I have a question about the SVT CL preamp section.

Here it is: I've just bought a set of JJ tesla, (1x) 12au7 and (2x) 12ax7, because I did a mistake during the order... I should have bought a couple of AU7s and a single AX7, as written in the rear panel of the head. Anyway, I've tried to substitute the old tubes with the one I've bought, but the AX7s make the preamp to distort at about 8 o' clock of gain pot. So I put back one of my old AU7s and the thing works on.
By the way, I've seen on the manual that inside the amp there should be 2 more AX7s, which make the preamp section, while the 3 tubes i can see on the back of the head should be the drive tubes... now, is that right, or am I misunderstandig something??
Plus, if there are 2 more tubes, where are them and how to get'em out?

Sorry for the long post, maybe there was already a similar thread, but I couldn't find it!

Cheers, dudes!

 

[demon666]

The pre amp tubes are up behind the controls. You have to remove the amp from the head box. The tubes out back near the power tubes are driver tubes.

 

[vit]

Thanks, then!
One more question... 'd be useful to replace those two tubes, in order to get a different sound? which between the preamp and the driver tubes affect more the sound?

 

[vit]

Moreover, how do I reach the inside of the front panel? Do I have to remove all 4 screws ont he top of the head? and then the tray should slide out, right?