The EM1 is a magic eye tuning indicator. The control voltage swing required is 5 Volts to move from minimum to maximum shadow within the bowl of the screen.
The EM1 has the same characteristics as the TV4 except for the heater.
The other EM1 has a conventional domed envelope. This valve, like the EM4, has a recessed window that makes for an elegant design.
The internal construction follows the normal pattern for tuning indicators.
The Ct8 base is clean and clearly this is a new valve.
The wide glass tube envelope is 26 mm in diameter and, excluding the Ct8 base pins, is 73 mm tall.
References: Data-sheet & 1043. Type EM1 was first introduced in 1937. See also1937 adverts.
