Why would anyone want to build a valve radio, one that
doesn’t even pick up FM stations? If nothing else, to get a feel and
understanding for old-fashioned technology.
There are lots of people who are attracted to valve amplifiers
(particularly musicians) and lots of people busily restoring vintage radios,
television sets and all manner of thermionic technology. So why not build a
valve radio from scratch? Despite the relatively few parts the radio uses, this
is certainly not a toy and it illustrates how much performance you can get out
of just a few valves.
As far as its lack of FM reception is concerned, there were no
FM radio stations in Australia during the valve era! (While experimental
broadcasts started back in 1948, the first FM radio stations, 2MBS and 3MBS, did
not start transmitting until 1975).
The prototype radio is housed in a whimsical gothic cabinet
which pays homage to some of the "cathedral style" radio cabinets of yesteryear.
Some people will hate it and others will like it. If you’re in the first
category, then build a more conventional cabinet.
Why "Aussie Three"?
Here's the front view of the Aussie Three removed from its Gothic-style cathedral case. We're willing to bet that the vast majority of Aussie Threes built will remain in this state!
Well that’s a dig at the "All-American Five" concept that
emerged in the USA in the 1930s. As an alternative to the grandiose (and
expensive) timber cabinet radios that are the delight of collectors now, some
manufacturers started marketing the virtues of a basic, no-nonsense but
perfectly serviceable superheterodyne that the "regular guy" could afford; the
"Model T" of radios if you like. There was no RF stage (which wasn’t really
necessary in urban locations anyway) but any lack of sensitivity could be
overcome by connecting a decent aerial and earth.
The valve line-up was the now-classic rectifier,
mixer/oscillator, IF amplifier, detector/audio preamplifier and a pentode audio
power output stage.
Our Aussie Three uses three triode-pentode valves, deletes the
valve rectifier in favour of semiconductor diodes and adds a ferrite rod antenna
to come up with quite a respectable performance.
To any non-technical user, it’s just a radio: you turn it on
and it works! Despite its tiny PVC tuning capacitor, there’s surprisingly little
frequency drift, even right up at the top of the AM band. From my home in the
outer suburbs of northwest Sydney, it picks up all the Sydney stations with just
its ferrite rod antenna, all at about the same volume.