The Four-in-One is an early multiple valve. The Quadruple Valve Co made two types of valve in 1929 - three triodes and four triodes in one envelope. This exhibit is the four triode version as can be seen from the lettering on the base.
The four triodes were designed to be one HF stage, detector and two LF sections.
The initial selling price was 22/6.
The gettering obscures almost all of the interior. Note the black sealant between the base cap and the envelope.
The 12 base pins with one indented to give location information. Ten pins have wires attached.
The internal construction of four cylindrical triodes around the pinch. The top left triode is had to see (and to photograph).
Micrograph of one triode showing the support wire folded to hold the grid helix.
The balloon envelope is 54 mm in diameter and, excluding the 12 base pins, is 100 mm tall.
References: Data & 1043. Type Four-in-One was first introduced in 1929. See also1929 adverts.
