The EL71 is a sub miniature output pentode. These valves were used in professional and military equipment. As the valve gets very hot in use it is recommended that the valve be encased and connected to a suitable heat sink. This exhibit is tightly fitted into the heat sink.
This valve was extracted from the audio amplifier of a military transceiver.
The corrugated metal conductor between the glass and the outer heat sink allows the glass to expand safely. The data-sheet says not to bend the wires closer than 1.5 mm from the glass. Two wires were bent very close to the glass and broke off as the valve was moved. As one missing wire is the heater, the valve is now dead.
The main heat sink is 14 x 12.6 x 39 mm. The four tapped holes allow it to be screwed to the metal outer case of the amplifier module.
