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In Reply to: RE: I get no music out of mynewly built amp posted by DAK on October 17, 2016 at 19:12:52
190 volt drop across 100k is 1.9ma of plate current.
A 6j5 will not be very happy with only 1.9ma. of current. 8ma. would be more "normal".
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
Actually, the driver stage is an "RH" type , i.e., there is plate fb from the output tube anode to the anode of the 6j5. The fb resistor is also 100k. So, wont that make the plate load 1/2 of just the single 100k resistor?
Significantly, when i touch the input grid of the 6j5 with my DMM probe there is no sound. nothing, no click, hum, or buzz. zip, zilch, nada. I measured about 60vdc on the plate, and IIRC, 2vdc on the cathode, but i can't find my notes about that measurement, so not sure.
The odd thing is that i built this same circuit with 6sn7 instead of 2 6j5 and it worked fine. Pretty much the same part values and the same circuit but , that amp did not have fixed bias, it was cathode biased.
Edits: 10/19/16 10/19/16
"Significantly, when i touch the input grid of the 6j5 with my DMM probe there is no sound. nothing, no click, hum, or buzz. zip, zilch, nada."
That's really strange.
I assume you bias supply is referenced to ground.
I think you said the grid to bias pot resistor is only 13k?
This is not an answer to why you are getting no sound but why such a low value grid resistor?
There has to be something mis-wired.
Do you get anything using you meter at the output tube grid?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
bias supply is referenced to ground via 5.6k resistor
grid supply resistor of 6550 is 51k
When measuring the volts on power tube input grid (about -30vdc) there is definite tick when contact is made. That would indicate that the output tube stage is ok
What is the value of the cathode resistor for the 6j5 and what is the cathode voltage?Did you check/change the coupling cap? It might be open.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 10/20/16 10/20/16
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