The 100E1 is a neon voltage stabiliser. The current through the device is centred on 125 mA but can rise to 200 mA. For maximum life the 125 mA should not be exceeded in regular use.
The cylinders are held between micas discs.
The construction is a series of three concentric cylinders.
The wide glass tube envelope is 50 mm in diameter, and excluding the B4 base pins is 137 mm tall.
Reference: Data-sheet. Type 100E1 was first introduced in 1955. See also1955 adverts.