This battery powered receiver dates
from 1930 and is quite stylish considering its early date when
the norm was a rather boxy design.
Tuning was accomplished by rotating
this control which is connecting to a cheap solid dielectric
tuning condenser. I suppose the limitation on space precluded
an air-spaced component as much as the price. You'll note that
station markings are absent. This feature only appeared a couple
of years later once broadcast stations were allocated their own
the matching volume control which is actually a reaction control
for adjusting feedback. If you haven't had experience of this,
let me explain what happens. As the setting is moved away from
zero the set will gradually get more and more sensitive with
a tuned station getting louder and louder up to the point where
excessive feedback causes oscillation of the RF stage turning
the receiver into a transmitter. Station volume usually drops
off and is accompanied by a hiss. The aim is to move the control
to the point immediately before this happens.
Despite the very high cost of valves
and increasing patent levies on their number, manufacturers added
valves to make the set sound more attractive to well off buyers.
This receiver employs an internal frame aerial so it needs extra
overall gain to produce loudspeaker strength signals. Unfortunately
the loudspeaker is missing from this example. Early loudspeakers
used a high impedance coil that could be driven directly from
the output valve and, because the coil used extremely thin wire,
it was common for this to go open circuit either from corrosion
or from the output valve drawing excessive current. Most battery
sets used three batteries. An accumulator for the valve filaments,
an HT battery and also a grid bias battery. The grid bias battery
was usually around 9 volts and because its drain was extremely
low would last for many years. Its chief function was to negatively
bias the output valve to reduce its anode current with little
effect on station volume. If the battery eventually failed or
became disconnected it wasn't really obvious to the user but
if the output valve current became too high the loudspeaker might
fail. Before the speaker failed a user might wonder why his HT
battery wasn't lasting very long.
has two wavebands. Back in the 1920s and early 1930s broadcasts
were to be found in what are now termed "Long Waves"
and the low end of the "Medium Waveband". Once it was
discovered that broadcasts were reliable even at 200 meters or
less the wavebands became Long and Medium. Really long distance
communication was found to be possible at even shorter wavelengths
and by the mid 1930s the Short Wavebands (60 to 11 meters) became
popular. The switch below marked "Long" and "Short"
reflects the situation in 1930 and actually refers to what would
soon become Long and Medium wavebands. As you can see the wavechange
doubles as an on/off switch.
The underside of the case is fitted
with a turntable enabling the case and therefore the internal
frame aerial to be rotated for maximum volume or minimum interference.
The latter being important because in 1930 frequency allocations
hadn't been properly sorted out. Particularly at night when continental
broadcasts could be extremely strong it might be necessary to
null one out to reduce interference to ones local station.