This SW regenerative receiver has only 12 V for B battery. However, its performance is similar or better than usual regenerative receiver. Output power is good for headphones. It is easy to listen SSB, even on 18 MHz. It uses 4 Russian electronic tubes (6N3P) very similar to ECC81 / ECC85, but with a different pin code. I suggest to use tubes with a slope of 5 mA/V or more. The main characteristics are :
1 Ground grid RF amplifier to avoid dead spots, body capacity and tunable hum, because there is great isolation of the antenna from the detector and the regenerative triode.
2 Unusual detector between diode and plate detector. This detector has a very good signal to noise ratio, but a low input impedance.
3 A separated tube for regeneration. Note that the grid leak resistor is connected to + B. Note the 220pF capacitor for the 12 – 19 MHz band to obtain a good frequency stability.
4 Band set and band spread tuning capacitors.
5 Four triode AF amplifiers. The output transformer is a small 230V / 6V transformer.
This receiver has a good signal to noise ratio, a good frequency stability, a good output power (for headphones) and no dangerous voltage. If you like regenerative receivers, try it !
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Electronic tubes can be used with “B” voltage less than the usual 250V. Best tubes for low “B” voltage are tubes with high transconductance and high plate current. Tetrode or pentode designed for power audio amplifier like 6V6, 6L6, EL84(6BQ5) have these criteria. I chose 3 EL84. The first EL84 is a ground grid RF amplifier. The second EL84 is an ECO regenerative detector and the third an AF amplifier. This is an old 1V1 designed to receive all bands from 3 to 18 MHz, but optimised for the 3 ham bands 80 40 20 m.. The RF amplifier is untuned, except for 20 m and 80 m to avoid interference from broadcast stations in the 41 m band. Two series-resonant circuits are used. To avoid 50 Hz frequency modulation when the detector is oscillating, the 6 V AC line must be centre tapped and 2 RF chokes must be used in series with the filament of the detector. Ham bands must be received with more than 200 pF of CV1 capacity to obtain a good frequency stability. To decrease the tunable hum the 47 nF capacitors in the power supply are necessary. A drive reduction is necessary for CV2.
The results may be greatly improved by using an audio preamplifier. The receiver becomes an 1V2.
Olivier Ernst F5LVG