Crystal Radio Kit

This vintage crystal radio kit was manufactured in 1975 by the Humbrol Mindstrand Company, and was part of their "World of Discovery" series. It consists of a kit of parts and instructions to build a germanium diode based crystal radio set. These types of radios are extremely popular and eBay is usually the place to find some of the best kits that work. Many of the electronics labs by RadioShack, and John Adams will also have such a radio for building. Just follow the link to see which ones have this as a project.

A crystal set is a very basic radio, with minimal number of parts, however, these days just a handful of components can amount to many pounds, consequently buying them separately to make a homemade set can turn out to be an expensive venture.

The most critical parts in a crystal set are the tuning capacitor and antenna coil. They connect together to form a tuned circuit that operates within the AM frequency band. Therefore, the value of the tuning capacitor, antenna coil thickness, ferrite rod size, will affect the frequency band you can receive. A ready-made kit usually has all the correct components of the correct size and are usually much cheaper and therefore worth considering.

This vintage kit is an interesting design because it eliminates the requirement for a tuning capacitor and a ferrite rod, which are expensive parts these days. In this design, the coil winds around a cardboard tube throughout its length. Removal of the coil insulation along one edge provides a means for a point contact to tap the signal. Tuning simply involves taking the signal from different places along the coil. The only downside with this design is the point contact, which makes intermittent and poor connection with the coil, which results in you having to hold it down to make an electrical connection.

The photograph above shows my completed kit. The blue coloured plastic had warped whilst in storage all these years and I decided to leave it like that because straightening it may cause it to snap. The reception is good providing you have a very good earth and a roof aerial. I was able to receive three stations in an area where there are many strong radio signals.

Instructions

The instructions are very clear, and there is plenty of useful and educational information. The manual consists of a single folded broadsheet.

Antenna Kit

The most critical part is the antenna coil. In this kit, they provide a pair of rubber bands to secure the ends of the coil when you are winding it. These rubber bands are extremely old, and one snapped just as I finished winding the tube. The result was a huge tangle of coil, which required winding again. The second time round, I used tape to secure the coil.

Germanium Diode

In this kit, you get a lovely point-contact germanium diode. A crystal set must have a germanium diode in order to work. There are many other types of diodes, which are silicon, which will not work.

Buy / eBay

Vintage kits are often available on eBay, and worth getting. Sometimes, you can get a nice set of parts that work very well. For example, this kit came with a vintage crystal earpiece, which they do not make anymore. Whilst you are there, you can also look for new kits to build.

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