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The VMP4G is a variable μ screened amplifier pentode for RF and IF amplification in superhet receivers.

The partial silvering on the glass allows some inspection of the structure.

Originally the whole envelope was covered in a metal paint. This has broken off to reveal the etched identification applied to the glass itself.

We also have the Catkin version the VMP4K.

The pinch holds the supports, the anode is two small vertical plates mounted either side of the central screen. The screen has the older style metal end plates but the original screen made of woven wire mesh has changed to a series of wires between the end plates.

The Type designation etched into the glass in typical M-OV style. Inside can be seen the ends of the screen grid wires as they pass over the end plates.

The control grid is close wound with no obvious widening of the pitch to offer a vari-μ characteristic.

The classic envelope is 44 mm in diameter and, excluding the B7 base pins, is 122 mm tall.

References: Data-sheet & ¹⁰⁴³. Type VMP4G 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.