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CRYSTAL RADIOS

My first encounter with semiconductors was a Germanium 'point contact' diode, a small glass bulb with a couple of wires sticking out of it. It was unbranded and unmarked and bought for a few pence (the old sort) from a local army surplus shop. If you look closely at the photograph (this is a much later type) you can just about see the small pointed spring wire pressed against the tiny Germanium crystal.

Within a few days I had a built a crystal radio from plans in one of those ‘101 Things for Boys to do’ books some aunt or granny had bought for me. The radio was literally nailed together on a piece of wood and comprised a hand wound coil on an empty toilet roll, a variable capacitor from an old valve radio, some ancient bakelite headphones and a 50-foot wire strung up in the back garden.

To this day I still get a kick out of crystal radios and recently managed to track down a couple of old models that I used to own as a kid. The Ivalek (right and below), which actually dates from the 50s, was made by the long defunct Ivory Electric Company and was a real find. My brother had one, which I coveted and he later generoulsy sold it to me for the princely sum of two and sixpence, as I recall…

This particular one is quite an early example, a proper Bakelite case job with a gallium arsenide crystal that has to be ‘tickled’ with a curly wire on the end of the little red knob. Finding a sensitive spot is something or an art and more often than not the only thing you'll hear in the earphones is the sound of your own hair growing but it's all part of the fiun.

The next cryastal radio, badged H&G AG-220 (right) is very similar to one I once owned (this model was produced in dozens of different guises) it uses a germanium diode and was incredibly sensitive. The aerial was my bedspring and I well remember listening to Light Programme and Home Service (now Radio 2 and Radio 4) broadcasts late into the night.

Sadly my one is missing a tiny jewel on the front, otherwise it is in excellent condition and works really well. From a technology standpoint the crystal earpiece was the real breakthrough. These oddly shaped flesh-coloured devices were unexpectedly loud (and very tinny) but a huge improvement on the bulky headphones of the day.

If you open up these radios there’s not much to see, but the little H&G is a brilliant example of minimalist engineering. There are just three components, the diode, a capacitor and the tuning coil with a sliding ferrite rod, controlled by the knob on the front -- brilliant stuff! The design is also extremely clever in that it doesn’t require an earth connection, which could be difficult to arrange unless there was a gas pipe to hand.

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