The 12AY7 is a double triode designed for low level audio amplifier stages.
The stage gain of 44 is around half of that obtainable with the 12AX7 type of double triode. This lower gain is deliberate so as to offer an alternative to the 12AX7.
The control grid has copper supports but more interestingly the anode has a small working section pressed deep into the wider heat sink. This construction was seen in the past only on valves for high frequency operation. SeePC86 for an example.
The triode sections are separated by an electrostatic screen, again an RF valve device.
The thin glass tube envelope is 22 mm in diameter, and excluding the B9A base pins is 49 mm tall.
Reference: Datasheet. Type 12AY7 was first introduced in 1949.