There is yet another resistor, in series with the capacitor to the
mixer signal grid. Not sure why these changes were made, evidently has
to do with the bias or with the change from a chassis ground to a
separate B return. Might help to draw out a simplified version of the
schematic.
The S-38 series seems to have been very popular, my B performed
quite well. I never had the National equivalent, the SW-54, but from
what I've read it was a dog. The neighbor who inpired me to get an S-38B
changed to an SW-54 but he was a rich kid who didn't really know
anything about radio. The SW-54 mechanical bandspread is supposed to be
just awful. They made only the one model while Hallicrafters kept poking
at the design.
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On 11/7/2024 2:46 PM, don Root wrote:
Richard and all ,later again
Oh? whatever I thought I saw? must have been an apparition
I took the time to copy ?the RF section of the B and C side by side? and
now I have to agree with your
“The C also shows a 470K resistor from the hot side of the switch to the
cabinet ground. _Not sure why_.“
At first I thought it was something to do with grid 3 bias, but now I
see there is a new resistor tucked in there
It seems that in the C version the Tune cap frame and rotor along with
the chassis has RF ?floating above all else using capacitors while C24
provides the RF return to B-minus. I have run out of thinking power, but
here is what I have been using recently. Do you spot anything?
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
