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  #31  
Old 03-27-2018, 04:44 AM
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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.
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  #32  
Old 03-27-2018, 10:17 AM
dieseljeep dieseljeep is offline
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Ok, either side of the 330 resistor it blanked out the audio all together.
Did it blank out the hum? If so, the hum originates from the audio circuit.
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  #33  
Old 03-27-2018, 10:29 AM
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Did it blank out the hum? If so, the hum originates from the audio circuit.
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.
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  #34  
Old 03-27-2018, 12:50 PM
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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.
Since that is the last audio stage, there would not be much/any hiss when it's input (the grid) is grounded.

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
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  #35  
Old 03-27-2018, 01:25 PM
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Originally Posted by jr_tech View Post
Since that is the last audio stage, there would not be much/any hiss when it's input (the grid) is grounded.

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
What I did was put the grid back on pin 5 of 25l6 then jumped from the grid to either end of the said 330 ohm resistor, the grid was put back on when I did this and it blanked out so now you want me to use a 470k or so resistor from pin 5 to either end of the 330 ohm resistor while the 330 is still in place, correct? So really it's just raising the value of resistance in that area. Ok I got it, lol between grid and the 330.

Last edited by timmy; 03-27-2018 at 01:50 PM.
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  #36  
Old 03-27-2018, 01:57 PM
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Yes, but the grid should be disconnected from the couplate.

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  #37  
Old 03-27-2018, 02:22 PM
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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  
Old 03-27-2018, 03:35 PM
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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.
Is the hum as loud as when the grid is connected to the couplate?

jr
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  #39  
Old 03-27-2018, 04:04 PM
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Is the hum as loud as when the grid is connected to the couplate?

jr
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  
Old 03-27-2018, 04:24 PM
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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.

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  #41  
Old 03-27-2018, 04:48 PM
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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
tube in and out, unplugged I get no resistance at all from any of the pins to pin 5 couplate off the grid. Yes a real head scratcher I already ran out of options. From tubes to diodes to capacitors to checking the volume control to the .370k resistor that is supposed to be 330ohm, nothing, it won't give up anything. I already clipped a few ceramic disc and dogbone caps at the ground to see if one may be leaky but so far nothing , clipped still humming. The ones I clipped one by one I believe we're at the heaters to ground.

Last edited by timmy; 03-27-2018 at 05:00 PM.
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  #42  
Old 03-27-2018, 05:32 PM
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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  
Old 03-27-2018, 05:36 PM
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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) ?
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.
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  #44  
Old 03-27-2018, 06:20 PM
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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  
Old 03-27-2018, 06:48 PM
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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.
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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