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Vintage Radio

Developed during the very early days of radio, reflex circuits were used in receivers right up until the 1950s. One such set was the Astor KM.

By Rodney Champness, VK3UG

Reflex RECEIVERS were sets that used one of their valves to perform several functions. In fact, some early receivers had more than one stage reflexed. In the case of the Astor KM, it’s the intermediate frequency (IF) stage (6B8G) that performs several functions – ie, IF amplifier, detector, AGC and first audio stage.

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Despite using quite conventional components, radios with reflexed stages were not particularly popular with servicemen. To understand why, read the early "Serviceman Who Tells" articles in "Radio and Hobbies" which came out from 1939 onwards (now available on DVD from SILICON CHIP). My own experiences with this set back up those early Serviceman stories.

The servicemen of the era were usually self-taught. Some of them had a good understanding of the radios they serviced but others were purely "valve jockeys". A "valve jockey" had no understanding of the workings of the receiver and just replaced valves until (hopefully) the receiver worked. Valves weren’t as reliable back then as they were in later years and valve jockeys often got sets going reasonably well, even if the real cause of the fault had not been found.

Another problem for early servicemen was the lack of test instruments. During the 1930s, even a basic multimeter was an expensive item and this situation persisted right up until the 1960s.

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