Ralf Siemieniec's (Brösel) Homebrew Radio

This year I decided to start the first time with an active radio. The radio is my tube receiver, so far my one and only tube project ever. The initial circuit was found in a amateur book which was quite popular and hard to get in former east Germany during the eighties when I was a young boy.

It follows the standard circuit used in many variations during the fifties – using a ECH81 (6AJ8) as mixing stage, a EF89 (6DA6) in the IF stage, a EABC80 (6AK8) as rectifier and AF pre-stage and a EL84 (6BQ5) as AF power stage. I added some modifikations, namely a RF pre-stage employing a tuned bandfilter using an EF183 (6EH7) and a magic eye since a tube radio must have a magic eye.

Building the radio needed a noteworthy part of mechanical and wood works which took its time. Also the electrical part needed some care and caused some troubles. For some time I was hunting for the reason of the rather strong oscillator frequency drift until I figured out that my shielded wiring was making the problem – the capacitance of these wires was extremely sensitive to temperature, so I removed all of this stuff again.

Spending time for a good alignment did really pay-off. Sensitivity of the radio is quite good, I was impressed that I can hear also really distant stations. Compared to my crystal radios used in the other contests, I enjoyed the simplicity of one-knob tuning a lot. However, it is not 100% true since also the ferrite antenna needs to be aligned for the best position.

Conditions were changing, as usual at this time of the year there were many thunderstorms in the region adding some less nice noise level from the lightnings. At some times in the night I found got DX conditions, getting in a lot of relatively weak spanish stations, one first-timer from Northern Ireland and a decent number of middle-east and north-african stations. Unfortunately, I had to notice that again many stations were shutdown forever, being formerly based in Germany, Italy, Belgium, Bulgaria, Sweden, UK and so on. Sad but true …

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