The type 77 is a general purpose pentode voltage amplifier/detector. As a high impedance device the control grid is taken to the top cap for maximum isolation from the anode circuit.
Sylvania describe the Type 77 as a sharp cut-off pentode similar to 6J7G.
The Sylvania branding printed on the base.
The screening prevents seeing the inner electrodes. Note the head radiating fins on the control grid supports.
The classic envelope is 39 mm in diameter, and excluding the UX6 base pins is 97 mm tall.
References: Data-sheet & 4059. Type 77 was first introduced in 1932. See also1932 adverts.
