The 20P3 is an audio output valve designed for single end use in universal mains receivers. The 200 mA heater indicates a cross over between radio and television equipment. The probability is that 200 mA heater chains were to be found in small VHF monochrome television sets.
The Mazda valve was designed after the time when Mazda gave up their own version of the octal base and adopted the standard International Octal.
The cathode resistor was designed to be 180Ω and the anode load to be 3,700Ω.
We have the 10P14 in the museum and it has identical operating characteristics and pin connections and was designed for a 100 mA heater chain.
Made in England on the glass. Below the lower mica are screens and grid electrodes are seen to be wound on copper supports.
The lower mica components with tape connections to the control grid.
The wide glass tube envelope is 28 mm in diameter, and excluding the IO base pins, is 76 mm tall.
Reference: 1040. Type 20P3 was first introduced in 1952.