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The POVT73A or GPO No.73A is a telephone repeater triode. The design dates from 1937 and the directly heated filament is oxide coated.

This exhibit seems to differ from the STC 4020A only in the fact that the STC identification has been omitted.

At full size the faint lettering can be seen. The VT.73A is quite clear. Also etched is W40/1.

The shape of the grid winding can be seen but the gettering obscures most angles of view.

The triode side view. The filament tension spring is retaining an intact filament.

The unmarked base cap, badly corroded pins and the pinch.

The pinch with additional glass tubes and in this image the filament can be seen.

The grid supports are held at the correct spacing by a horizontal bar. The bar itself is spot welded to the main top grid support.

The balloon envelope is 57 mm in diameter, and excluding the American 4-pin bayonet base pins is 101 mm tall.

Reference: Data-sheet. Type POVT73A was first introduced in 1937. See also 1937 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.