Hi there,I believe the T runs at -55 vdc for bias.To adjust it you need a volt meter,small screwdriver and a little bit of knowledge.What's important here is plate current draw,you might want to invest or make your bias probe to measure plate current on your output tubes.If you replace 12AX7A's with 12AT7's you'll get less gain.The ax's are hi gain,the at's are lower,good luck Mel.