Electrostatic Swivel Speaker

Employed in combination with Philco consoles H-1814, H-1816 and H-1916.

The speakers use a thin flat diaphragm consisting of a plastic sheet coated with a conductive material such as graphite sandwiched between two electrically conductive grids, with a small air gap between the diaphragm and grids. For low distortion operation, the diaphragm must operate with a constant charge on its surface, rather than with a constant voltage (charge and voltage are not the same thing). This is accomplished by either or both of two techniques: the diaphragm's conductive coating is chosen and applied in a manner to give it a very high surface resistivity, and/or a large value resistor is placed in series between the EHT (Extra High Tension or Voltage) power supply and the diaphragm (resistor not shown in the diagram here). However, the latter technique will still allow distortion as the charge will migrate across the diaphragm to the point closest to the "grid" or electrode thereby increasing the force moving the diaphragm, this will occur at audio frequency so the diaphragm requires a high resistance (megohms) to slow the movement of charge for a practical speaker.

The diaphragm shows in total ~6760 tiny perforations, the two front covers feature together ~31,590 microscopic orifices (~24156 upper, ~7434 lower).

The upper section can be swiveled 90 degrees left or right.

Unique 5-pin connector.
Speaker code : 36-1685-2
Material: Housing plastic, front covers brass plated iron.

In questo link sono elencati 4014 modelli, di cui 2208 con immagini e 3662 con schemi.
Elenco delle radio e altri apparecchi della Philco, Philadelphia Stg. Batt. Co.; USA