The Type A from Siemens was developed from the French hard valve towards the end of 1917 after samples were captured. Like the earlier inefficient German valves the workmanship is of high quality. Five basic designs were made: two designs from AEG, two designs from Telefunken and the Type A from Siemens and Halske.
The main image shows this unused example s/n 2868 in the original box with shredded paper packaging.
The connections at the top end of this image are labeled A and G for Anode and Grid. The anode is a flat plate maintained a constant distance from the ladder type grid by both being held in glass rods. The filament is a single strand supported from the other base.
Rotated through 90 degrees. The sprung brass contacts and the shaped mouldings can be seen.
Rotated trough 90 degrees again. This shows the underside of the base(s).
A final 90 degree rotation.
The filament end showing the brass connections screwed to the base and the twisted wires soldered to the connections passing into the base shell.
The anode and grid connections are identical to the filament end.
The top pinch, base and Siemens logo.
A close-up of the filament connections. The wires pass into the white cement inside the Bakelite base shell.
The ladder grid looks to be corroded and would thus indicate a loss of vacuum.
The glass electrode support fixed to the pinch stem. The glass holds both the anode and grid in place. The anode is connected to the pinch by stout wire.
Another view of the anode connection.
The geometry of the triode. The filament is shaped but has no tension spring or other support to maintain the position relative to the grid.
Seen from this angle both the grid and anode connections through the pinch can be seen.
The label was tied to the valve by thin cord. This had rotted away at the eyelet. The only parameter present is the filament current for this bright emitter.
The reverse of the label showing the serial number. It is believed that 50,000 of the Type A were made in total.
The wide glass tube envelope is 37 mm in diameter, and including the base pins is 108 mm tall.
References: Internet. Type Type A was first introduced in 1917.