This AT50 is a directly heated transmitting triode from M-OV with GEC on the envelope as well. The original was the M-OV T50 with flying leads and developed in around 1923.
This valve was made for the UK Army - AT is Army Transmitting - and has a 50 Watt anode dissipation with up to 1.5 kV on the anode.
The S3 base. The connection on the right is the control grid.
The screw anode connection.
The anode with the control grid and single hairpin filament within.
Looking up from the base the feint lettering is just visible. The filament rating is given as is the Type designation.
Microscope image of the filament support hook. Note also the method of attaching the grid winding to the three supports.
The filament tensioning spring.
Part of the grid support mechanism.
The fine wire wrapped round each grid turn and the support rod.
This example seen on the internet looks unused whereas our exhibit has blackening on the envelope from the evaporating filament.
The base connections - Image courtesy of Fin Stewart.
The balloon envelope is 76 mm in diameter and, including the S3 base connections, is 193 mm tall.
References: 1003, Data and valve envelope. Type AT50 was first introduced in 1925. See also1925 adverts.
