The ORP90 is a 1950s Cadmium Sulphide photoconductive cell. Basically a light dependent resistor with the incident light arriving aligned with pin 4. The data sheet describes the target application as flame control and ignition detection. This Mullard device was made by Philips in Holland.
The maximum voltage across the resistor can be 300 Volts and the dissipation is 1 Watt maximum at 25 °C falling to 0.3 W at 70°C. The more usual operating voltage would be 10 Volts. The dark current is given as 2.5 μV. The device is most sensitive to red light and at a colour temperature of 1500°C is twice as sensitive as when illuminated by a Tungsten filament lamp at 2700°C.
The metal frame is just present to hold the board with the light sensitive resistance.
The pattern of lines just divides the surface into one long strip.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 53 mm tall.
Reference: Data-sheet. Type ORP90 was first introduced in 1958. See also1958 adverts.
