OC45/OC71 Germanium Radio

Ok, after browsing the “MDS975” website that I stumbled upon by chance recently, just had to have a go at the “Ladybird Radio” – I remember this slightly differently, though I believe its basically the same design, by the Rev George Dobbs (G3RJV) this was however featured in a BBC TV series “Why don’t you switch off your TV set and do something more interesting instead?” that aired in the early ‘70’s.

A teenager had enthusiastically built one of these, and explained how (memory is a bit misty though, but it would seem that the detail was a bit lacking at the time), but I got my father to send the SAE for the design…

I got it to work after some time, (no help from said Father who wanted me to play the trumpet!) and treasured it for some time. It got thrown out by said parent years ago, but then …. Why not look back to the past and have another go, especially with the Practical Wireless article about early transistors..

Ok – had some old “OC71” type transistors (£1.50 about 7 years ago from the much missed Longleat radio rally) that turned out to be unmarked – just plain black, and only 3/10 tested ok…

Only thing to do was to get an OC45 (treasured because of fuzz boxes apparently – as if we men don’t have enough facial hair already) for around £2 on ebay, and build the beast…

Works quite well – reasonable volume of “radio 5 live” into the speaker more or less first time… the only real difference between mine and the original is that I could not rustle up such a low value trimmer for the RF feedback bit, so used a 4.7 PF capacitor instead (oh well- no adjusting)


Click here to see larger version of the germanium radio
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Click here to see more of the germanium radio


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