The 12B7 is identical to the 14A7 as can be seen from the double identification on the dome of the envelope. An early all glass construction pentode it was introduced in 1940, probably by Sylvania in America.
The 7A7 is identical except for having a 6.3 Volt heater.
This variable μ valve was designed for high gain signal amplification, at RF and IF in broadcast receivers.
Champion was a reseller of valves as the etched Sylvania name clearly shows.
The envelope dome showing 14A7 and 12B7.
The wide glass tube envelope is 29 mm in diameter and, excluding the B8B base pins, is 56 mm tall.
References: Datasheet & 4059. Type 12B7 was first introduced in 1940.