Here is a moderate power triode used in a lot of military equipment during WWII as either an oscillator or class C amplifier. Plate dissipation is around 5 watts with a power output of 4 or so as I remember. 12 volt filament requirement (was frequently matched with some 1625's as in the ARC 5 command sets. Might make a dandy audio driver with some manipulation of the bias voltage. Various manufacturers, RCA, Western Electric etc.