10-09-2011, 05:56 AM
The filter caps find DC ground via what looks like resistor #52. (up and to the right from the xfmr center tap) That puts their negative terminals several volts 'above' ground and that voltage is used for biasing.
What I mentioned before is the ground path for any residual audio/IF that may be on the B+ line. You'll note that there are no other bypass capacitors on the B+ line up to R24 - and then there is #5 for bypassing beyond that resistor. In theory #21 could be placed anywhere along the B+ line. But, as Richard said, that particular arrangement may have been best for preventing spurious oscillation.
What I mentioned before is the ground path for any residual audio/IF that may be on the B+ line. You'll note that there are no other bypass capacitors on the B+ line up to R24 - and then there is #5 for bypassing beyond that resistor. In theory #21 could be placed anywhere along the B+ line. But, as Richard said, that particular arrangement may have been best for preventing spurious oscillation.
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