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.
The side terminal and the box anode within the balloon envelope. With the launch of the New Process in September 1929 Cossor moved away from the shaped anode of the Stentor range to the box anode. The latter being easier and cheaper to make and offering a better fixing arrangement for the improve filament.
This view clearly shows the construction method. The filament is two inverted hairpins held with springs placed above a top mica. The three wire grids pass horizontally in front of the filament. The broght box anode is formed from two sheets crimped together.
The filament tension springs.
The grid shape is clear.
The shaped black composition base is a Cossor design.
Here the pin construction can be seen together with the solder at the tips to connect the lead-out wires.
The balloon envelope is 50 mm in diameter, and excluding the B4 base pins is 104 mm tall.
References: 1043 Type 230PT was first introduced in 1929.