The 808 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 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 grid supports are connected to a collar that sits aroind the pinch stem. The grid connection to the side cap as made near this collar.
The metal anode with side flanges. The close wound control grid is clearly visible and with effort the bright helical filament can be seen.
The balloon envelope is 70 mm in diameter and, excluding the UX4 base pins, is 135 mm tall.
References: Datasheet & 4061. Type 808 was first introduced in 1938.