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The 703A is a power triode for generating RF at up to the UHF region.

The filament runs vertically and is held under tension by a spring arm. The anode is finned and semi-circular at the apex of the triangular fins. The grid is helical and held to a vertical support opposite the open end of the anode.

A Japanese company (Yamamoto Sound Craft Corp.) has, in 2012, offered new bases for these valves and suggested their use for audio. With an anode load of 5,000 Ω HT of 377 Volts, grid at -21.6 Volts setting a current of 37 mA an output of 1 Watt is claimed.

Side view, the glass distorts the view of the inner structure.

The base - The filament pins are top right.

The filament runs top to bottom. The grid is supported on one side only and close to the anode. The anode has two heat radiating fins. The design looks similar to the original Cosmos Short Path.

The balloon envelope, also known as a doorknob, is 52 mm in diameter and, excluding the special base pins, is 40 mm tall.

References: Data-sheet.

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.