Cayin A50t biasing problem

Larry, are you saying that you have a 15 to 20ma reading regardless of the rotation of the bias pot(s)? Or that is the maximum reading available? Is there any difference in the reading between the 4 tubes/locations? You know it is entirely possible that your have some seriously exhausted tubes. Do you know their history? Do you have any spares - you could always sub in a good one and see what happens.

Hi Newbee....I rotated in three different quads including a new quad of SED winged c's and what I am getting is a maximum of about 20ma. Being in all four pots is puzzling.

Larry, There is something in the bias circuitry that is common to all four pots. The meter! I'm not thinking it is broken, though it might be. What I'm thinking is that something between it and the pots is defective, for example the switch where you select the pot you want to adjust or, more likely, the connections between the switch and the meter. Just a guess. Maybe you need a techie to take a look.

I have 2 meters so I don't think its the meter. There isn't a switch to select the pots so I can't figure this out

Larry, I doubt that this is an issue, but are you taking your readings off your meter using the DC ma setting? That would make a big difference in your readings. Other than that I'm baffled right along with you.