Cayin A50t biasing problem

The pot travel of 3/4ths of a turn is not unusual. Three of my amps do this, including a Cayin. The bias curcuit not functioning at all is a different matter. I don't own a A50t so I don't know but is it possible the bias circuit is seperately fused and a fuse has blown? Is it possible that the previous owner blew out a resistor(s) in the bias circuit that might affect all of the pots? You might take off the lid and see what is there. After its fully discharged of course.

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.

To answer Williamredburry idea...I do have a very small reading of about 15-20 MW so I think I have a circuit connection...Newbee, you might have something but since I have a low reading, I think it may be a faulty bias circuit but it is kind of odd it would be in all the pots. I had one once that had 1 bad one. What do you think?

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.