The P220A triode from Mazda is a low wattage audio output valve for battery radio receivers. The load impedance is 4,100 Ohms and the power output is given as 350 mW. It is the bigger brother to the P220.
The identification on the dome.
Thanks to Mark Mallison for sending the images.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 91 mm tall.
References: Datasheet, 1040 & 1043. Type P220A was first introduced in 1931.