Hey guys, thanks for the interest in the head.....to answer your questions, the screen grid resistors had drifted values, due to the abuse of this amp before i bought it it was nessacary to change them, also it had the original tung sol 6550's but once again due to some fool owning it before me, they were pretty shot. i do still have them though. all my work is done by jerry pinelli of FJA mods here in syracuse. hopefully that answers some questions...thanks adam