Phils other set
The Crystal Set Building
Built by Philip Miller Tate (aka 'Ge_Whiz') 2 January 2001
Free-style Category / General Class
On New Year's Eve 2000, I was perusing the Building Contest web site, when I noticed that no-one had submitted an entry to the 'free-style' category. Like all good British sportsmen, loving the cut, thrust and parry of an uncontested event, I resolved to do something about this. On New Year's Day 2001, inspired by the general detritus of the Season still littering the house, I set out to throw together, with as little care as possible, the cheesiest design I could come up with. As you can see from the pictures, it could not have been much cheesier than this.
Who cares? I mean, let's face it, I could have built a full-blown 'Mystery' in there, but that would have taken too much effort. The circuit used is so simple, I can't even be bothered to draw it. Parallel tank circuit, diode and crystal earpiece. In deference to Owen, to show that I have learnt something over the last year, I did tap the diode half-way down the coil. In further deference to my American colleagues, I used a genuine non-magic-bullet 1N34A.
The radio was inspired by that four-inch diameter 'Cheese Football' box. I could have wound the coil on the box, but that might have obscured the classic decorative design, so instead it was wound on a smaller cardboard roll which originally held that tacky felt strip stuff used to stick Christmas cards to the wall.
The tuning capacitor is built into the box, and consists of a 6 inch-by-1.5 inch strip of aluminium foil (could have been from the turkey) taped half-way-round the inside of the box with a similar strip, protected by acetate, rotated around the outside. This rotation is accomplished by the cunning incorporation of a four-inch diameter lid from a jar of supermarket cashew nuts (thanks for the idea, Dan), the perfect accompaniment to a good, cheap sherry during the run-up to the Big Day. The whole assembly is held together with Christmassy sticky tape. Everything else was either mounted on the wall of the box (machine screws for aerial/earth, earphone socket) or just lobbed into the box. The coil was glued to the original box lid, and fell off during construction.
With a sixteen-foot indoor aerial, the radio receives three local stations and can clearly separate them. Almost. Well, it does tune a bit. The limited coverage is due to the fact that I underestimated the capacitance of the foil capacitor, and hence overwound the coil, so the top frequency is not much more than 1MHz. I could have rewound the coil, but why bother? It wasn't meant to challenge a superhet. With a 120 foot aerial, it receives the same three stations, but louder. Frankly, I'm amazed it worked at all after three hour's construction time (including tea break).
I hope that this entry does not encourage anybody else to submit something to this category. If they do, I will have to hastily acquire a full-blown workshop, and insist that the entry be bumped up to the 'Master class'.
Cautionary note: I warn anyone against attempting to copy this design. Those cheese footballs were so yukky, only my wife would eat'em.