Одноламповый приемник прямого преобразования на 7MHz.
I picked up many valves on the broken TV-sets on the street about 30 years ago. I got many 12BH7A on them. In these days (in the end of 1990's) I made a radio to receive 7MHz SSB and CW signal with these valves stocked. 12BH7A can make his job with only 12V on it's plate. See fig2! Half side of 12BH7 oscillates the 6.9 to 7.2MHz CW with ECO oscilator. It is injected to RF port of a single balanced mixer. On the other hand, 7MHz signal is injected on the RF port of the mixer. Therefore an audio signal comes on the IF port of the mixer. This signal is amplified by the other side of 12BH7A. Single balanced mixer convertor has 10dB loss. An audio amplifier has 38dB gain. Total gain of this radio is 28dB. I could receive the domestic SSB and CW signals clearly with dipole antenna.
Kazuhiro Sunamura, (JF1OZL)