[AI2V]

The audio stage was probably rewired for use with a 6F6; the 6V6 didn't gain much radio use until after 1940; it doesn't really matter since the wiring for both is the same and the output power is roughly the same in general use.

As a cheap and common alternative I sometimes use the cooler running 6K6 in these audio stages; these are the long lived audio tubes used in the 1950's TV's. All three, the 6F6, 6V6, and 6K6 use the same wiring. If you want slightly higher volume (and heat) a 6L6 will also work.