Ts4d Motorola

[timmy]

Originally Posted by jr_tech

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.

[jr_tech]

Yes, but the grid should be disconnected from the couplate.

jr

[timmy]

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.

[jr_tech]

Originally Posted by timmy

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

[timmy]

Originally Posted by jr_tech

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.

[jr_tech]

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

[timmy]

Originally Posted by jr_tech

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.