The 230PT (formerly the 230) is an audio output pentode from cossor and the B4 with side terminal version dates to 1929. In 1933 a revised version was issued on a B5 base. The 230PT produced 0.4 Watts.
Our other 230PT is of later construction with a box anode. Here the construction harks back to the earlier days of tetrode construction.
The anode is formed from a pair of plates either side of the central electrodes. The suppressor grid can be seen as a ladder of wires between supports.
The central box structure is the screen grid. Note that there is just one filament tension spring.
The suppressor grid as two sets of wires hooked around the supports.
The layers of grids with the oxide coated filament at the centre.
In the top right of the picture is the second filament tension spring.
The balloon envelope is 45 mm in diameter, and excluding the B4 base pins is 96 mm tall.
References: 1043 Type 230PT was first introduced in 1929. See also1929 adverts.