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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.
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