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Realistic 10 TRF

Realistic 10 TRF

This shocking red radio isn't from Tandy, nor is it a TRF. Measuring 167x96x43mm and weighing 700g (8oz), it was made in Japan for Technical Apparatus Co., Inc of Boston, Massachusetts.  The US Civil Defence markings on the tuning dial put the date of manufacture to be pre-1963. The case is made from heavy cardboard covered with real leather.  The 10 transistor superhet circuit covers medium wave only approx. 540kHz to 1600kHz.


The circuitry is very unusual for a pocket radio. A glance at the polyvaricon tuning capacitor reveals three trimmers.  Yes, it's a three gang unit, because this radio has an RF amplifier (preselector) stage.  The mixer is unconventional as well as it employs a separate local oscillator, a single transistor circuit in the familiar Reinartz configuration. Following the mixer are two stages of IF amplification, a diode detector, one AF amplifier, driver and transformer coupled balanced push-pull output stage with temperature compensation by thermistor.  Unusually for a pocket radio, a "phono in" socket is provided in addition to the usual one for the earpiece.

Two AGC systems are used, the first being a standard reverse AGC circuit using the average positive potential derived from the detector diode to back-bias the bases of the RF amp., mixer and first IF amp.  However a second AGC loop uses transistor V12 (the one shown wired common-base under the detector diode) to partially shunt the RF amp's supply to ground under strong signal conditions, reducing V1's collector voltage.

Needless to say, with circuitry more akin to that you'd expect to find in a communications receiver rather than an old pocket radio, performance is excellent. I only wish it had long- and short wavebands as well.  The nearest UK equivalent battery seems to be the long-discontinued PP4.  However a PP3 can be used with adaptor leads. I get the impression this radio was originally designed for use in remote areas far from centres of population where mains power was unavailable.

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