The VP133 is a variable-mu pentode for RF and IF amplification in broadcast superhet receivers. The 200 mA heater requirement and low anode voltage places the design use for this valve as universal mains receivers without a mains transformer. The variable-mu characteristic is designed so that the stage gain can be altered by virtue of altering the bias on the control grid. AGC systems would provide this variable bias according to the strength of the received signal.
The VP133 was introduced in 1938 but appears as current in the post war advert of 1948. British industry took some time to bring out new receiver designs after the end of the war and several set makers offered pre-war designs in the late 1940s. Typical was the 1945 Sobel 615 with a large wooden cabinet and the Bush DAC90 AC/DC set in a Bakelite cabinet. By 1950 radio sets had moved, in general, to being the smaller DAC90A style with miniature valves.
The reverse is plain zinc loaded paint for screening.