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A note: looking at the various handbooks for the E version I find a
major difference in the first E and the Mark1 and 2 versions, namely the
arrangement of the BFO. In the first one an arrangement similar to that
used in the B is found, namely stray capacitance in the form of gimmick
wires are used to cause the IF amplifier to oscillate as a regenerator.
In the later version a pot is inserted in the suppressor grid of the IF
amp to control its gain and cause it to act as a regenerator. This will
also affect its selectivity. The control is on the back apron of the
receiver so it can be adjusted at will. The pot is listed in the parts
list. The schematic from BAMA for this series is pretty bad. I don't
have a better.
I find it interesting that Hallicrafters engineers took so long to
figure out the adjustable regenerator set up. The original S-38 has a
separate BFO of the conventional sort, with a diode in the tube acting
as a noise limiter. The B version eliminates the separate BFO and makes
the IF stage oscillate through capacitive coupling. This eliminates the
additional tube. Evidently, with the second E version they went to the
idea of making the if into a regenerative detector. This provides a beat
oscillator but it also can be used to narrow the bandwidth of the IF by
careful adjustment of the BFO control. Still gets rid of the extra tube
but, of course, sill eliminates the noise limiter.
The B type circuit can still be adjusted for best selectivity but
its a matter of moving wires so, once done its pretty much fixed.
Its interesting to me that Hallicrafters kept tinkering with the
design of many of its receivers.

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998