Welcome! Need support, you got it. Or share your ideas and experiences.
69.253.77.163
I have a Mk III that has developed an issue, so looking for a little help.
On power up, the bias goes up properly then, after 1-2 minute warmup, I lose about 1/3 of the bias when measured via the power/preamp socket.
I put bias sockets under the KT88s, and found that when the bias drops I completely lose plate current to V1 (the KT88 nearest the edge) and the plate current to V2 goes up as a result.
Anyone know what may be causing that?
Follow Ups:
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.
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
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: