The VT13C (later renamed the CV1562) is a directly heated transmitting triode for use up to 6 MHz. The VT signifies the old RAF service code pre 1941.
It is believed that the VT13C was the first valve to use the L4 base.
The blackened inside of the envelope is due to the deposition of filament atoms as the filament boiled away and eventually fails.
The Air Ministry Crown logo.
The horizontal anode cylinder has a30 Watt dissipation. The control grid is supported on one side only and the filament was a single strand through the centre of the grid.
This side of the filament is intact and the thickness of the wire holds it in position.
Here the pitch of the grid winding can be seen as the grid extends beyond the end of the anode.
The grid winding is fixed to the support at each loop by the notch and peen method where a trough is cut and after laying the wire a roller pushes the displaced metal back over the inserted wire.
A closer view of the grid.
Top view showing the electrode geometry.
The balloon envelope is 56 mm in diameter and, excluding the L4 base pins, is 86 mm tall.
