The X81 is a triode hexode mixer for use in communications receivers. The triode oscillator is designed to produce 10 volts pk-pk to drive the hexode mixer. The all glass envelope is protected by an all encompassing aluminium screening can that also serves to hold the spigot carrying base in place.
The Osram paper label is on the opposite side to the printed type designation.
We had another X81 in poor condition and so we sacrificed it to reveal the all-glass valve within the aluminium can. With the lower can peeled away the cement holding the bulb to the can can be seen as a brown line round the valve. The foot is moulded to provide a firm anchorage for the can and plastic pin cover and spigot.
The valve out of the can. The pins are solid and moulded into the hard glass foot. The sealant was applied as two narrow bands.
The gettering obscures the electrodes except from the sides. The actual envelope has no markings to identify it.
Seen from the other side the triode is at the top and the mixer a separate assembly between the triode and the base pins.
The wide glass tube envelope is 32 mm in diameter, and excluding the B8B base pins is 59 mm tall.
Reference: 1040. Type X81 was first introduced in 1947. See also1947 adverts.