The Y63 valve is housed in a classic shaped envelope with the electrodes held in a glass pinch with the leads leading to an International Octal base. The Y63 was for mains sets and parallel heater connections. The operationally identical Y64 was for AC/DC sets and this suggests that the heater was controlled for both Voltage and current.
The magic eye display hows the circular display and the target at the centre. The triode section is clearly visible in the main picture and requires a grid voltage change of 22 volts for maximum visual change. The display is green. See CV51 for the nearly identical Y65. The Y65 had increased sensitivity requiring 11 volts change for full deflection range and is the second generation type of this indicator with a 6.3 Volt heater which found use in many radios most famously the Lancaster receiver the R1155..
These devices are hard to find today having good emissive properties, all examples offered for sale will be shown by two photos - an envelope shot and a lit shot with the device photographed on test on our AVO VCM163 with the correct anode load (1M Ohm).