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The Pen36C audio output pentode is a B7 version of the CL4. The CL4 has a Ct8 base and the valve was also issued with an International Octal base as the CL33. The B7 base was issued in 1933 and this valve was designed in 1935 for use in AC/DC sets wit no mains transformer and a series heater chain.

Mullard tended to add the Suffix -C to a type fitted with a non-standard base cap for sale in a particular market and this may be true here. If so the valve originated with Philips in Europe.

Thanks to Mike Edwards for sending these images.

This exhibit has a slightly rounder envelope compared to Pen36C.

The classic envelope is 42 mm in diameter and, excluding the B7 base pins, is 116 mm tall.

References: Data-sheet & ¹⁰⁴³. Type Pen36C was first introduced in 1935. See also 1935 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.