The 803 transmitting pentode was made for government use only, and this suggests a special quality version. The maximum anode dissipation was designed to be 125 Watts and in Class C RF amplifier mode it could produce 155 Watts of output power. The design dates to the late 1930s and most transmission at the time was confined to the HF bands up to 30 MHz.
The electrodes are held in place by a collar placed around the pinch stem. This style of construction was effective but resulted in long leads and thus increased lead inductance and consequently a limit on the operating frequency.
The graphite anode and ceramic supports indicate high voltage and significant anode dissipation. looking at the base and pinch the connecting wires are braided.
The top ceramic insulator and two helical filament tension springs. The anode is approximately 2 mm thick.
The wide glass tube envelope is 64 mm in diameter and, excluding the base pins is 214 mm tall.
Reference: Data-sheet. Type 803 was first introduced in 1937. See also1937 adverts.