Hallicrafters "S21 Skyrider 5-10"

 

 This fine old receiver made in 1939, in original drab livery (could be described as dried mud), tunes to two VHF bands, 25 to 40 Mc/s and 38 to 66Mc/s and has all the features one would expect in a communications receiver.

 

 The valves used are octal types, with the exception of the UX4 rectifier, as follows:-

RF stage... 1852 (same as a 6AC7); Mixer... 6L7; Oscillator... 6J5GT; 1st IF... 6K7; 2nd IF... 6P7G; Det/AF... 6Q7G; AGC... 6H6; Output... 6F6G; Rectifier... 80.

It's a single conversion superhet with an IF of 1.6Mc/s.

You'll note a Woden auto-transformer sitting on top of the mains transformer because this set was designed for 110 volts AC.
 

 Above is a pretty basic under-chassis layout which looks simple because of course only two wavebands are covered.
 

 Incidentally, that alternative name Skyrider 5-10 refers to its coverage of the 5 and 10 meter amateur bands, one of which was to be at risk when TV broadcasting expanded, and by 1949 was no more, to be replaced eventually by the 4 meter band.

Above you can see the dial gearing arrangements using twin gears sprung together for anti-backlash.

 

An advertisement from 1939, and not what we understand as an Ultra High Frequency receiver nowadays. In fact the standard HF receivers from Hallicrafters tuned to around 45Mc/s so this set offered only a small extra coverage, although with its 1600Kc/s IF, image strength would be reduced. I'd need to test the set to see exactly how well it responds to FM because it appears to have an ordinary AM detector. Presumably in its broad selectivity setting one tunes off centre to resolve FM signals. Its 1852 (=6AC7) RF amplifier is said to enable reception of signals as low as 1 micro-volt.

Slightly puzzling is the fact that the 6K7 is missing from the valve line-up. My guess (unless it's a mistake) is that it was added to provide an extra stage of IF amplification to improve performance following complaints from its users?

 

 

 Click to see four pages of technical details for this receiver

 

 I've never seen quite so many patents listed for a receiver. It seems a "catchall" label because it says "If" and "one or more", as well as "pending"... clearly taking no chances.

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