Old Radio Parts-page 2

More old radio bit and pieces


Coil holders and push-pull on/off switches

 

 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.


Crystal detector

 

 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!


Tuning condensers

 

 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.


Valveholders

 

 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!


Gramophone parts

 

 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?


 Early electric motor

 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.

 

 


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