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The General Coverage 550kHz to 30MHz SWL Receiver SW-717 was a Low End or Beginners Receiver that came on the market in 1971 and was produced until 1982. The SW-717 was a Solid State design and it replaced the Tube design GR-64 that came on the market in 1964, which in turn replaced the GR-91 that came on the market in 1961.


My receiver suffered heavily from hum. The main reason was that the aluminum chassis was used as the zero voltage reference and also as a conductor between components. I have connected copper wires between the components and also replaced the original mains transformer with a toroid transformer. The toroid transformer is better in general but the difference it made in this case is negligible. Instead it was the use of the aluminum chassis as a conductor that caused the hum. The band-spread mechanism was of poor design and did not work. I have redesigned it and now it works.
SW-717 schematic

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