Air Tight ATM-1 schematic, bias setting and tube

Hello,

I live in Italy and I have an Air Tight ATM-1, serial number is 01427.

After 10 years of good service the amplifier needs assistance because the new valves (Svetlana) became too red in few minits and the technician needs same informations how to regulate it or the electronic scheme.

AIR TIGHT is not imported in Italy and I do not have any official assistance.

Are the Golden Dragon (Svetlana) good for my ATM-1?
What else I can use?

Sorry for my bad english

Francesca