The Z749 is a screened amplifier pentode, the GEC name was used as the professional brand of M-OV. The Z749 is directly equivalent to the EF812 and closely related to the EF80. TV and radar receivers would require wide bandwidth RF amplification.
This exhibit was Made in England and little of the internal structure is visible within the perforated metal outer screen.
The internal screening includes a lower plate by the anode lead.
The thin glass tube envelope is 21 mm in diameter, and excluding the B9A base pins, is 58 mm tall.
Reference: Datasheet. Type Z749 was first introduced in 1959.