The 808 is a magnificent specimen. Built as the early triodes with a vertical anode, this valve was designed as an RF power amplifier or power oscillator. It can be used at full input up to 30 MHz and with reduced input up to 130 MHz. The filament is of thoriated tungsten and runs at 7.5 Volts and 4.0 Amps. The anode is substantial and glows cherry red at maximum input, the insulators are ceramic and the grid is connected to a side contact. The grid is a set of three support wires fixed to a ceramic spider, upon which the helical wire grid is wound. The maximum negative grid voltage is -400 Volts.
The valve is marked JAN808, the JAN being a US Government quality code. The 808 had been discontinued by 1960 in favour of the 812A. The best date of introduction is 1938 but it was probably earlier.
The grid connects to the side cap with metal tape.
The anode with close wound grid. The grid supports are attached to the ceramic insulator.
The thoriated tungsten filament is helically wound.
A closer view of the grid and filament.
The balloon envelope is 70 mm in diameter and, excluding the UX4 base pins, is 140 mm tall.
References: Data-sheet & 4061. Type 808 was first introduced in 1938. See also1938 adverts.
