December 2000

My December column was mainly about letters and comments I'd received during the year. However, there was one brand new item: a photograph of a lovely little variable-frequency, electron-coupled oscillator/transmitter made by Johnny Apell SM7UCZ. It uses a 6L6G with 200V-300V on the anode, and produces 2W-3W output on 3.5MHz. In this type of oscillator, the anode circuit is tuned to either the second or third harmonic of the grid frequency. If expertly built and handled, such an oscillator can produce a signal almost equal to that of a crystal-controlled oscillator. The photograph shown here is one that didn't appear in the magazine. It's © Johnny Apell SM7UCZ. Click on the image to see a full-size copy (66K jpeg). Click here for the circuit diagram (41K gif - this is A4 size, so it may be best to choose save to disk and look at it later). If you think the 6L6G looks a little strange, then you're not alone. The glass envelope's 'shoulder' is higher than you'd expect. This may be an early example of a 6L6G.

One unusual piece of documentation came to light during the year. I'd previously been asked if I knew anything about a tuner/amplifier made by the Magneta company of Leatherhead in Surrey, UK. The equipment had been found in Bavaria by Juergen Bittner, and I wondered how it had managed to get so far from home. I did discover that the Magneta Time Co. Ltd. used to manufacture and supply public address equipment to the NAAFI (Navy, Army and Air Force Institutes) although the set in question seemed a little young for that explanation. As it turned out, that was indeed the answer. During restoration work on the set, Juergen found a little poster inside the set entitled: 'Navy Army & Air Force Institutes. Notes on care of a Billiard Table'. Click on the image to get the full poster (82K jpeg).

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