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In Reply to: RE: Mk III Bias Loss on One Tube posted by baileyler on October 30, 2014 at 11:30:33
Is it the original Dynaco circuit topology or has it been modified? Swap the tubes from one socket to the other and see if the problem follows the tube.
Follow Ups:
It is the original circuit other than the selenium rectifier and multisection cap (both have been replaced).
It is not the tubes as the problem has occurred with a couple of different sets.
Did the problem start suddenly after the amp ran fine for a long period of time, or did it follow the parts replacements you mentioned?Check the connections to the socket where the problem occurs and then trace the leads back to wherever they came from to make sure the solder connections are good. Lug # 3 is on the plate and I think it should be either a blue or blue/white wire. Lug # 8 is on the cathode - but check all the wiring to and from the socket, just the same. The socket contacts might need retensioning.
I'd want to measure the internal voltages against the chart in the original manual. Of course, don't go inside at all unless you are familiar with safe work practices around lethal voltages.
Edits: 10/31/14 10/31/14 11/01/14
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