Privat-Ear Pocket Radio

The Privat-ear radio is a two-tube battery powered AM radio that was designed only for earphone use.  It was made by the Privat-ear Corporation, and was introduced in 1950.  It is pocket sized, and is about 6 inches high, 2 1/4 inches wide, and 7/8 inch deep.  It requires two AA cells and one 22 1/2 volt battery (about the same size as a standard 9 volt battery) for operation.  

Privat-ear radios are found with either a New York address molded into the case, or a Blacksburg, Virginia address.  It's not clear which came first, or why they relocated.

The left knob controls the volume and the right knob is the tuning control.  The 18 inch telescoping antenna also serves as the the power switch.  The plastic case was available in red and maroon, and probably other colors (though the sales brochure only mentions maroon).

The Privat-ear fits neatly in the breast pocket, with the knobs conveniently exposed, but the antenna must have been distracting as it bobbed around a few inches away from the user's left cheek, and the earphone is quite uncomfortable. 

The radio works well enough, though, giving ample volume on local stations.  It's selectivity is not good, it tends to oscillate, and the antenna must be all the way out for best reception.  Battery life is short-the AA cells were good for only about 10 hours of use.  Forgetting to push the antenna all the way in was an expensive mistake.

Tubes like the type 2E31 subminiature tubes used in the Privat-ear were developed by Raytheon during WW-II for use in proximity fuses (electronic devices which caused shells to explode in the general vicinity of metal objects such as German V-1 "buzz bombs" or enemy aircraft).  Their first civilian use was in hearing aids which appeared during WW-II.  The first consumer radio to use subminiature tubes was the 1946 Belmont "Boulevard".  The Privat-ear was the second.

A tiny device invented by Bell Laboratories in 1948 was destined to doom battery-hungry tube radios such as this.  The first all-transistor radio appeared in 1954.

This appears to have been Privat-ear's only product.  A factory invoice that was with this radio indicated that this one had been sent to a Philadelphia store as a sample.  It would be interesting to know whether an order for more radios followed.  Somehow, I don't think so.

The Privat-ear used a reflex circuit, in which one tube served as an amplifier both at RF and audio frequencies.  This tube has copper wire wrapped around it, apparently to function as a shield.  Some of the tubes they used had silver colored conductive paint on them which had the same effect.  A germanium diode was the detector (the white object at the far left).  The second tube provided additional audio amplification, sufficient to drive the single crystal-type earphone.

The radio is tuned by moving the iron cores in and out of the two coils.  They are operated by a dial cord driven by the pulley at the left (just below the diode).  The radio was not designed to be serviced-the tubes were soldered into the circuit.  The only alignment that could be done involved moving the coils with respect to the cores and gluing them in place again.  Even so, the tuning was inaccurate, so a calibrated dial was out of the question.

To their credit, the designers used no paper or electrolytic capacitors in this radio, so as long as the radio is undamaged, and the tubes are not burned out, a Privat-ear should work as well today as it would have when new.

Shown here is the original sales brochure for the Privat-ear.  Click on each image for a larger version.

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