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The 5B/254M miniature beam tetrode was designed to have the same ratings as the classic 807. The difference in size between the 807 and this valve shows the extent to which valve technology matured during WWII and the effect of the introduction of the pressed glass base. This particular base was the earliest to be developed with eight equi-spaced pins and an external metal collar to hide the envelope seal and provide a locating spigot.

The valve is also very similar to the STC 5B/251M and electrically identical to the 5B/255M. The latter has the anode connected at the base and one less connection to the cathode.

The wide glass tube envelope is 30 mm in diameter and, excluding the B8B base pins, is 85 mm tall.

References: Data-sheet & ¹⁰⁴⁰. Type 5B/254M was first introduced in 1957. See also 1957 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.