The TZ40 is a magnificent audio triode that was designed for high power audio use in class B. A pair would deliver 175 Watts at 5% distortion.
The signal input would be 220 Volts peak to peak between the two grids. The anode load would be 7,000 Ohms.
It is quite possible that the main use for this device would have been modulators for small AM transmitters. The data-sheet is for the very similar DA41.
The TZ40 was a development of the earlier T40, also with a 40 Watt anode dissipation but with a gain of 25 whereas the TZ40 has a gain of 62.
The shaped graphite anode is held between ceramic insulators. The top cap is much larger than the receiver types.
The top of the valve. The graphite anode is a smooth oval inside and the grid can be seen to be close wound. Below the filament tension springs can be seen the tops of the two inverted V filament strands. The filament passes through the grid four times. Note that the anode connection passes into a glass tube and not directly through the envelope.
The top of a filament loop can be seen. The wire is bright with no trace of oxide and this fits with the DA41 description of a thoriated tungsten filament.
The lower ceramic support and pinch. The centre filament support is a hook fixed into the ceramic support. The anode cannot be welded so a series of metal tubes with flat tops are crimped onto the supports.
Mark Mallison has sent this image of the TZ40 on a ceramic base.
The balloon envelope is 51 mm in diameter and, excluding the UX4 base pins, is 149 mm tall.
