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06-07-2020, 09:20 PM
Hi
if you are going to retain the redundan bias supplies then each needs a zener clamp. You should be able to use a single bias supply for both tube sets. Adding the zener makes the maximum negative voltage independent of the bias-set networks, leaving it open for you to modify the range of one network without it effecting the other... too much.
There is always a bias interaction with pairs of tubes, so the best tact is to set the firt by meter then set the second by ear for minimum hum. Doing a cross-zero between the push-pull pair may set DC idles the same, but this is not the same as the hum-balance point for the OT.
if you are going to retain the redundan bias supplies then each needs a zener clamp. You should be able to use a single bias supply for both tube sets. Adding the zener makes the maximum negative voltage independent of the bias-set networks, leaving it open for you to modify the range of one network without it effecting the other... too much.
There is always a bias interaction with pairs of tubes, so the best tact is to set the firt by meter then set the second by ear for minimum hum. Doing a cross-zero between the push-pull pair may set DC idles the same, but this is not the same as the hum-balance point for the OT.
