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Mark 4A
Jan 9, 2021 15:43:19 GMT -5
Post by danpetty on Jan 9, 2021 15:43:19 GMT -5
Turned my mark 4a on and no noise out of the receiver.Meter still works,Transmitter still working.
Any ides where to start,trying to find a local tech and not much luck yet......thanks,dan
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Post by 2600 on Jan 10, 2021 1:49:06 GMT -5
I would start with a glance at the tube just behind the speaker, the 6AQ5. It is the hottest-running tube in the receiver, and will eventually wear out the tube socket. The spring contacts in the socket lose their spring temper from hundreds of heat/cool cycles. If the heater in that tube is dark, a slight jostle to the tube sometimes gets it to light up again. A shot of non-residue contact cleaner, or even 91% isopropyl from the drug store to the socket may help. Inserting the tube, with some in/out motion before the solvent evaporates can help scrub some of the oxide schmoo away from the contact surface. A brush tiny enough to fit inside the socket's openings will be hard to obtain.
If you feel decent friction against pulling the tube out of the socket, that's a good sign. And if the tube just "slips" out when you pull on it, that's not so good. A lack of friction tells you the socket is worn out.
73
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Mark 4A
Jan 10, 2021 12:00:34 GMT -5
Post by danpetty on Jan 10, 2021 12:00:34 GMT -5
Thanks for the reply. The tube still gets hot and there is restriction when taking it out of the socket. I will try to get a new tube to try... thanks,dan
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Mark 4A
Jan 10, 2021 21:53:27 GMT -5
Post by oldgeezer on Jan 10, 2021 21:53:27 GMT -5
The 12AX7 may have failed or the external speaker jack has poor connection. Clean the jack normally closed contact by prying open and close on a piece of thick paper coated with contact cleaner and pull thru with contact closed on the paper.
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