I own a A55T. When I bought it i was told to use sharp ( pointed) electrodes to do the measuring. If it has a blunt tip it won't measure anything. Maybe this helps. Good luck.
Cayin A50t biasing problem
I recently purchased this amp on a'gon and having trouble getting it bias. When try to measure the bias I get no reading on any of the pots. When I try to raise the bias, the travel of the pot is very small like 3/4 of a turn. Is this normal. I have had many tube amps so I think I understand the process. I can't believe I have 4 bad pots nor 4 bad tubes. What give anyone?