The BTH B5 is a triode that was first released in 1923. It is a general purpose valve and has an μ of 7. The filament rating of 2.8 Volts was chosen so that the valve could be heated by two dry cells in series.
Unlike our other two B5 & B5 exhibits this one has a slightly transparent coating that reveals the inner electrode structure. The vertical anode is of small diameter with the single strand filament at its centre.
In 2010 another B5 with a clear side to the envelope has been found. The anode is revealed as a long thin cylinder.
The glass bead insulator is held in place by a rod to the pinch
The grid is held to a single support. The filament is a single central strand.
The balloon envelope is 38 mm in diameter and, excluding the B4 base pins, is 88 mm tall.
Reference: 1003. Type B5 was first introduced in 1923.