You missed the 100k resistors that alway go to the junction of R60 and R62.
One provides a path for the V6A grid bias. Both also bootstrap the filter circuit.
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jerrylong;5132545t said:
Yes, notice that the positive feedback from the cathode circuit bootstraps
(increases the effective AC value) the 100k resistors. Since the AC voltage
across them is reduced, their effective AC resistance is increased.
The last 100k also gives a DC path for the grid bias voltage (the drop across the 680R).
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Yes, it looks like that. I would remove the whole circuit, use the last 100k, and just one coupling capacitor
before it of a reasonable size, maybe 0.05uF to 0.1uF.
No, so if you want to eliminate the entire filter circuit, remove all of the parts between
the volume control wiper and the tube's grid. Then add one series coupling capacitor
(0.05uF to 0.1uF) from volume control wiper to the grid. Also add a 100k resistor
from the grid to the junction of R60 and R62. That's it.
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Here's the result of deleting the filter.
https://www.digikey.com/schemeit/project/c22-9GJIM08301O0/
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