The top two have a lever allowing a pair of coils to be adjusted for mutual coupling so that the best reception could be gained by trading sensitivity and selectivity
Switches like these were used universally in wireless construction before the toggle switch similar to the type used in house wiring of the day found its way into a constructor's junk box.
This is a
crystal detector assembly which enclosed a germanium crystal and
a thin springy wire called a cat's whisker. The small universal
joint at the left allowed the cat's whisker to be set to a point
on the crystal which gave rectification of signals. A receiver
using such a device was either a simple crystal set which would
provide sufficient output to drive a pair of high impedance headphones
or sometimes included an amplifier valve which could drive a loudspeaker.
In either case the longer the aerial the better and together with
a good earth connection would pick up stations within a radius
of 20 or 30 miles. It is sometimes reported that if a small battery
was used in the crystal circuit improved results could be had.
If this had been investigated properly then transistors would
have been invented 40 or even 50 years earlier!
The shape
of the vanes was important as a square law applies when tuning
across a radio band. Unless the condenser was carefully shaped
you would get a lot of cramping at the higher end of the dial
where often most stations were.
To get a nice linear gradation of scale a square law was invoked when designing the shape of the condenser blades.
As you can see, apart
from the WWII B7 ceramic base which came from an R1124 VHF receiver
using a row of 8D2 valves, the remainder are mainly B4 types and
were designed for mounting on a baseboard. This was the standard
method of home construction during the 20s, often with an ebonite
front panel. Valve manufacturers continued to use the B4 base
for many years. The centre pin, making the base a B5 was resisted
by some for ages. If a "screened grid valve", or tetrode
as it became known later, was designed it often used a top cap
for the control grid and a side screw connection for the screen
grid. To make matters most confusing valves were often available
in B4, B5 or B7 configurations and carried the same code. Not
only was a particular valve available with different numbers of
pins but it may be either metallised or just plain glass and some
were even made completely from metal with no glass. All a bit
hit-and-miss if you ordered one by post and forgot to specify
exactly what you wanted! Buying modern semiconductors can have
much the same hurdle nowadays. The code letters after the typecode
are often more important than the typecode. Different versions
may be surface-mounted, lots of dual-in-line legs, alternate heat
sink shapes, different operational temperature ranges, and different
firmware (that's unchangeable program code) contents!
An assortment of old
gramophone components including two pick-up arms, a driver into
which a needle was inserted for a horn reproducer and what looks
like another early type of moving coil pick-up.
In the late 20's one could purchase the parts necessary to build your own loudspeaker. These consisted of a driver unit, like the one shown near the centre of the picture, and a circular sheet of stretched material held in a frame for the speaker cone. Thus for around a couple of pounds or so instead of several weeks wages you could have the luxury of not having to don headphones to listen to your wireless. Parts were really expensive for the average working man for several reasons; these included royalty payments to Marconi, license fees to the BBC (including even an experimenter's license); stringently maintained resale price maintenance; and the exclusion of (cheap) foreign imports. Every valve in your radio carried a surcharge for Marconi and this in itself helped perpetuate popularity of the crystal set.
If transistors had been invented 20 years earlier what would this have done to Marconi's profits I wonder?
Amongst the parts I found in an old box was this electric motor. The design is typical of motors which were around at the turn of the century until the mid 30's employing a stout brass casing and in all sizes up to maybe 10 feet across. It doesn't use carbon brushes but as you can just see in the LH picture, pair of perforated brass pads soldered to brass springs. Field connections are brought out at the base. Was it used to drive an early gramophone turntable?
The diameter of the motor is about 7cm (a bit less than 3 inches). Any electric motor experts know its likely date?
If you drive a motor from an engine it becomes a dynamo, generating rather than consuming power. Anyone that had an old car fitted with a dynamo before alternators became the norm may remember what happened if you pressed in the regulating relay with a finger. The dynamo used to behave like a motor.
More old radio components
See some early mains connectorsSee more unusual things>>