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Sensibly equivalent to:
CV1637 LS5
See also:
Some Important British Valves - The American Shaw Radio Tube Base
Extras ▼


The Post Office type POVT25 is electrically equal to the Marconi-Osram type LS5 that was introduced in 1922 but the POVT25 was fitted with the PO-2 variant of the B4 base. In this exhibit the base cap is the original American Shaw base - the same as the PO-2 base.The CV specifications refer to GPO valves as POVT whereas the GPO used the form VT no. xx.
The Marconi identification etched into the glass and the Shaw base cap.
The locating pin of the bayonet base.
The standard LS5 construction with the filament tension spring at the top.
The sticker on the bulb identifies the valve as a VT25 - a totally different valve - Valve Transmitting a pre CV designation by the RAF.
The actual GPO Type designation is etched into the glass as VT No. 25.
Made in England.
The balloon envelope is 52 mm in diameter and, excluding the UV base pins, is 118 mm tall.
References: 4051 & 1004 Type POVT25 was first introduced in 1923. See also 1923 adverts.


Absolute Maximum Operating Conditions
PDF scanned from an original document held by the museum
Updated September 03, 2022.
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