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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?
128x128larryrx7
newbee
4,751 posts
 
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.
larryrx7's avatar
larryrx7 OP
137 posts
 
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
newbee
4,751 posts
 
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.
larryrx7's avatar
larryrx7 OP
137 posts
 
Yes but I am measuring voltage instead of current in this amp.
ttbolad
42 posts
 
Are you sure that your probes are touching the bottom of the bias test insertion points? On my amp the insertion points are quite close together. The probes get in way of each other and didn't reach to the bottom until I cut away some of the plastic that was sticking out from the side of the probes. Until I did that, I could not get a reading.
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