#31
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The resistor checks .370 k so that's off a bit from 330 ohm . Befor in another post I said it was .336 k that was incorrect however that didn't fix the hum. This is turning into a mystery.
Last edited by timmy; 03-27-2018 at 06:13 AM. |
#32
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Did it blank out the hum? If so, the hum originates from the audio circuit.
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#33
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It blanked out all as if no speaker was connected, or as if it were turned off. If the hum was gone there should have been other noise like a hiss when no antenna connected.
Last edited by timmy; 03-27-2018 at 12:17 PM. |
#34
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Quote:
Another experiment... instead of grounding the disconnected grid, insert a 470 k ( or so ) resistor between the grid and either end (try both) of the 330 ohm cathode resistor. jr |
#35
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Quote:
Last edited by timmy; 03-27-2018 at 01:50 PM. |
Audiokarma |
#36
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Yes, but the grid should be disconnected from the couplate.
jr |
#37
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Ok grid disconnected 470k from grid to ground side of 330 has hum to the other end of 330 blanked out, silent nothing no hiss.
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#38
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Quote:
jr |
#39
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Couplate on , hum, couplate off 470k to the ground end hum is Alittle less 470k to the other end of the 330 blanked out.
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#40
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I'm still thinking leakage in the tube or socket...
Another experiment: with the grid of the 25L6 totally disconnected, and the set off and unplugged measure resistance between the grid pin (5) and all of the other pins of the socket with and without the tube in the socket. This is turning into a real headscratcher. jr |
Audiokarma |
#41
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Quote:
Last edited by timmy; 03-27-2018 at 05:00 PM. |
#42
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Did you check between all the pins on the socket - not just to pin 5 ? Your meter might not be putting out enough voltage to detect any leakage. I don't suppose you have a megaohmeter or insulation tester (AKA Megger) ?
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#43
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I did check the socket very closely and the Dvom I have is very sensitive, voltage from the meter I don't know but the socket looks new for its age.
Last edited by timmy; 03-27-2018 at 06:16 PM. |
#44
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Maybe I should look at the other sockets maybe another one may show some carbon track, who knows at this point. For a hum I would think it would be obvious if the socket was bad but much higher voltages I would assume would show something on a socket but this problem don't seem like much ac is getting in somewhere because it's only affecting audio and not an image problem.
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#45
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Is that socket a "wafer" type socket? I have already experienced dealing with two bad sockets of that type developing leakage between the wafers. as a last ditch effort, why not try replacing the socket.
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Audiokarma |
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