"elaich" wrote in message
...
"Richard Knoppow" wrote in
news:Y8KdnfPtguP-
:
Since I undertook restoring an S-20R recently I
researched this receiver and its relatives. What I found
is
interesting: the same basic receiver was built in various
guises from 1939 to 1968!
Where does the S-77a figure in your timeline? I have one,
and it appears to
be identical to an S-40.
The S-77 is an AC/DC version of the S-40B. It dates
from the same period, about 1952. At one time DC current was
supplied in many areas of the US and other countries as well
as aboard ship so receivers capable of running on it were
made. There is also a cost saving where the power
transformer can be eliminated but I this this does not apply
to the S-77. Hallicrafters built several AC/DC models of AC
only radios. Radios operating on DC must have series string
heaters that add up to 117 volts or must have a series
resistor where the filament sring is not sufficient. Also,
the current demand of all tubes must be the same. Some
receivers, and I think the S-77 was among them also had a
balast tube to help drop the voltage and also stabilize it.
It was pointed out to me that the SX-25 was essentially
an S-20R with the addition of a crystal filter, S-meter, and
push-pull audio output stage. The later SX-99 and SX-110 are
essentially the S-40B with the crystal filter and S-meter
added but maintaining the single-ended output stage.
Hallicrafters sure got a lot of service out of that
design:-)
--
--
Richard Knoppow
Los Angeles
WB6KBL