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In Reply to: RE: need some advice ... posted by vinnie2 on July 31, 2017 at 16:00:48
PJ's commentary is certainly sage wisdom.
I would add that if you adjusted the 30K plate load and 340R cathode resistor on the first stage to get 75V on the plate of the first 6DJ8 triode, then you could dump a whole lot of parts from the amp (the two 1M resistors and 0.1uF cap are no longer necessary).
Follow Ups:
I tried doing this but the volume started breaking up out at about half throttle. I was able to get the plate to cathode voltage down on the first section by changing the plate resistor and leaving everything else the same per the schem. Tomorrow I will work on the other section.
Edits: 08/01/17
You'll want to adjust both the plate load and cathode resistor together. If you increase the plate load, your bias voltage will drop (potentially a lot), and that will limit the incoming voltage into the amplifier if you go too far (what's your bias voltage currently?). Also don't forget to leave that stopper resistor between the first stage's plate and the second stage's grid.
Yeah, I still have a bunch of work to do to get it working within specs, but now that I have the layout correct it should be easier. It already sounds pretty good too.
Not quite sure I follow you on that. I like to use as few parts as possible, so I would like to understand what your reasoning if you care to explain. Thanks.
The second stage needs to see +75V at its grid, and Broskie has added in the two 1M resistors and coupling cap to provide this.
If you adjust the operating point of the first stage you can change the voltage at the plate from 150 to 75, then this plate can be connected to the grid of the next stage (leaving the 300 Ohm resistor to prevent oscillations).
To make this change, you'd want to draw some load lines. I'd recommend looking at 47K and 75K.
Thanks, I will give it a try and a listen.
Try a 75K plate load and a 530 Ohm cathode resistor. That should give you about 2V of bias and 75V on the plate.
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