Ethatrope

Single Knob Receiver.
12 Pre-tuned stations selected by clockwise rotation whereupon the station name is illuminated.
Anti-clockwise controls the volume.
HF stage followed by SG detector, AF and Pentode output.

Description from Wireless World August 1932.

As illustrative of a tendency that is bound to become more pronounced in the course of time, the M.P.A. Ethatrope is in some respects one of the most interesting sets at Olympia. The basic circuit arrangement may be dismissed in a word by saying that it is a fairly conventional H.F. det.- 2 -L.F. arrangement, with an S.G. detector and band-pass input. Interest centres around the tuning system, which is controlled by a multiple switch, reminiscent of automatic telephone practice, which throws across each tuned circuit the appropriate amount of capacity required for any one of twelve predetermined wavelengths. The condenser, of the air- dielectric type, is tapped, and there is no relative movement of its vanes during the process of selecting a station.

But this is only half the story. The knob which controls the switch, when once set to close the appropriate set of contacts for a desired wavelength, may be rotated to a limited extent in either direction to control volume by altering bias; as clockwise rotation is further increased, the reaction comes into play. In fact, every operation is affected by this single knob, which also combines the functions of an on-off, radiogramophone, and wave-range switch.

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