The KT71 is an audio beam tetrode output valve that was designed for use in AC/DC equipment such as universal voltage radio receivers and television sets. It was issued in the early 1940's.
In single ended use an output of 5 Watts was possible with an anode load of 2400 Ohms. If used in push pull class AB1 a pair of KT71's would generate 11.5 Watts at 4.5% distortion.
The Marconi paper label.
Looking at the pinch and above. The cathode is rectangular and the heater is formed from insulated coils of wire that pass four times through the cathode. The control grid has copper supports.
The top mica with the control grid heat sink above. The S shaped ribbon connects the beam plates to the cathode.
The classic envelope is 44 mm in diameter and, excluding the IO base pins, is 103 mm tall.
