The DA60 power triode was designed for use in both public address equipment and transmitter modulators. The anode load is given as 2,300 Ohms and the output is 11 Watts in a single ended configuration. For both public address and modulation the valve would have been used in push pull and for higher power output in parallel push pull.
The DA60 is a directly heated triode with a thoriated tungsten filament. Direct heating was preferred as the direct heating of the active thoria surface layer gave a greater emission per watt of heating power than an indirectly heated valve.
The anode from the side, here the filament tensioning springs can be seen. The glass rod provides insulation.
The DA60 like other large valves has the anode supports brought down to a clamping ring that was manually tightened around the pinch before the envelope was attached. The etched inscription 'made in England' is easy to read.
The anode is not carbonised but has ridges pressed into it to give greater rigidity.
The grid wires do not appear to gave been wound with any significant tension as they are not held flat across the filament strands. The bottom filament tensioning springs can be seen as small hooks. Sadly the actual filament is broken and exists only as a series of straight wire strands loose in the envelope.
The L4 base with a well form example of the M-OV logo.
The top filament supports extend from the glass rod. The rod itself is supported on the curved rod emerging from the centre of the pinch. The vertical support is cross braced back to near the pinch. A significant piece of engineering and quite costly. The DA60 was clearly intended for professional or military use. The UK Navy used L4 based valves for both transmitters and ship wide public address.
The balloon envelope is 78 mm in diameter, and excluding the L4 base pins is 165 mm tall.
References: Data-sheet & 1043. Type DA60 was first introduced in 1929. See also1929 adverts.