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As far as we know this VT.1A valve is roughly equivalent to the M-OV Type T15 or perhaps the T15A (which had a slightly more open grid). The interesting thing about this VT.1A is the envelope shape which is characteristically Ediswan, early to mid 1920s.

Although Ediswan also used other shapes of envelope we do not think anyone but Ediswan used this particular, highly recognisable, shape. Later Ediswan valves of this shape were fitted with black moulded base caps in place of the earlier metal shell type.

This valve is was used by the Royal Air Force as a transmitting valve. It was made by Ediswan, and the manufacturers type reference is 1120. The serial number on the envelope is 1410. It is also marked Ediswan 'A'.

The electrode construction follows the conventional coaxial pattern within a horizontal cylindrical anode. The filament is corrugated for additional length, and therefore emitting area, within the anode.

The balloon envelope is 50 mm in diameter and, excluding the B4 base pins, is 95 mm tall.

References: ¹⁰⁰³. Type VT.1A was first introduced in 1919. See also 1919 adverts.

Pin Connections