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  #16  
Old 03-26-2018, 01:46 PM
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Do you still measure a high voltage between the chassis and b- ?

jr
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  #17  
Old 03-26-2018, 02:21 PM
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Quote:
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Do you still measure a high voltage between the chassis and b- ?

jr
No hv neg to chassis I obviously went from b+ to chassis. My mistake.
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  #18  
Old 03-26-2018, 02:49 PM
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What do you hear if you disconnect the grid (pin 2) of the 25L6 audio output tube.

jr
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  #19  
Old 03-26-2018, 03:40 PM
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Quote:
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What do you hear if you disconnect the grid (pin 2) of the 25L6 audio output tube.

jr
I didn't disconnect anything else but pin 2 of the 6sq7, still humming.
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  #20  
Old 03-26-2018, 04:17 PM
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I didn't disconnect anything else but pin 2 of the 6sq7, still humming.
So now i'm asking what happens if you repeat the experiment on the next (last) audio stage.

jr
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  #21  
Old 03-26-2018, 04:27 PM
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Are the filaments in series, or is it possible to pull the audio amp tube and see what happens to the hum? Do you have a tester to check the audio output tube for heater/cathode short, or a spare output tube?
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  #22  
Old 03-26-2018, 04:31 PM
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Well I could take off pin 2 but nothing will happen, heater. Or you meant grid I think ?
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  #23  
Old 03-26-2018, 04:32 PM
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Originally Posted by old_tv_nut View Post
Are the filaments in series, or is it possible to pull the audio amp tube and see what happens to the hum? Do you have a tester to check the audio output tube for heater/cathode short, or a spare output tube?
I tried 2 other tubes both of them and my tester does check for shorts. It is series.
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  #24  
Old 03-26-2018, 04:42 PM
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Well I could take off pin 2 but nothing will happen, heater. Or you meant grid I think ?
Yes, grid, pin 5, sorry for the confusion.

jr
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  #25  
Old 03-26-2018, 04:59 PM
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Pin 5 off hum even louder with no hiss as if there was no ant.
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  #26  
Old 03-26-2018, 05:16 PM
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Interesting.

What happens if you connect pin 5 of the 25L6 to either end of the cathode resistor (330 ohm R-38) ? Try both ends.

jr
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  #27  
Old 03-26-2018, 05:38 PM
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Interesting.

What happens if you connect pin 5 of the 25L6 to either end of the cathode resistor (330 ohm R-38) ? Try both ends.

jr
After the grid wire was put back on?
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  #28  
Old 03-26-2018, 05:48 PM
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Ok, either side of the 330 resistor it blanked out the audio all together.
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  #29  
Old 03-26-2018, 06:06 PM
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Well the 330ohm resistor checks at .336k so I have a new 330ohm resistor that checks just that so I'll change that resistor tomorrow. One end of that resistor goes the cap at the amp . maybe it cannot filter because of that resistor being high.
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  #30  
Old 03-26-2018, 06:09 PM
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Seems like it coud be leakage from the grid to the heater pins.

Is the socket dirty or perhaps charred? Bad insulation on wire to the grid?

jr

Edit add: Why change a resistor that is only 6 ohms off? That is less than 2% off.

Last edited by jr_tech; 03-26-2018 at 06:41 PM. Reason: add question
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