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#3
February 3rd 09, 04:06 PM
posted to rec.radio.amateur.boatanchors
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Hallicrafters S-20R, S-40, etc.
"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 |
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