I will show you that, the old triode can be used by low voltage about 12 volts. Please see the circuits. Regenerative radio in old days can make its activity by 17V-DC. Gain of detector (A to B) is 40dB. Gain of audio amplifier (B to C) is -16dB. Please see the old time regenerative detector (fig2). In this circuit, regenerative circuit, C2 and L2 is made by the resonance circuit. Therefore we must tune it, when we change the receiving frequency. Such a radio was used in Japan while the world war two. They were called as “NAMISAN”. “NAMISAN” means the standard three valve radio. The first valve 6C6 is used as regenerative detector. The second valve, 6ZP1 or 42 was used as audio power amplifier. The last third valve, 12F was used as power detector, in the power supply. All the Japanese heard announce of the end of the war with this type of radio. Please see fig1. In this circuit, regenerative circuit is made of high-frequency-transformer. Therefore, I have no need to tune it. In this radio, from 6MHz to 12MHz, regenerative ratio is constant. In this radio, case is made of glass-epoxy-board. I can hear BBC with 7MHz dipole antenna.
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