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The VR505 is an RAF triode as specified by the UK Air Ministry. The prototype was the MH41 a mains triode that has the 1930s UK standard 4 Volt 1 Amp heater. The valve low impedance device and designed for audio frequencies.

The VR505 was renamed the CV1505 with the advent of the CV register in 1941.

The internal coating precludes photographing the insides. Under strong light the anode is revealed as a vertical rectangular box that has been ribbed for dimensional stability.

The envelope shape strongly suggests a Cossor valve.

Looking at the top mica the cathode can be seen as a rectangular tube. The heater is coiled on itself to minimise the external mains hum - very important in an audio valve.

The balloon envelope is 45 mm in diameter and, excluding the B5 base pins, is 92 mm tall.

References: Data-sheet & ¹⁰⁴⁰. Type VR505 was first introduced in 1933. See also 1933 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.