The G-24 is an American valve. It is an indirectly heated tetrode and equivalent to the UY224 the first American indirectly heated screen grid valve.
The construction looks to be the same as the Arcturus 124 but with the clear glass the details are easier to see.
The details of the main electrode assembly are revealed. The solid insulation in the cathode protects the two strands of the heater. The screen grid is a cylinder that encloses the control grid and oxide coated cathode. The control grid can be seen within the fine pitched screen grid.
The balloon envelope is 45 mm in diameter, and excluding the UY base pins is 110 mm tall.
References: 3002 & 1047. Type G-24 was first introduced in 1927.