Western Electric service manual pages covering the 49-A & B amplifiers which show the original diagram with the 246A input transformer in the circuit, and the 700 apparatus box which contained the amplifier on the projector.
Around 1930 ERPI modified 49 A & B pre-amplifiers to accommodate 18 db higher output of the new 3-A photoelectric cells used in movie projectors. This modification bypassed the 246-A input transformer and also replaced the two 239-A tubes with the less microphonic 264-A tubes which also drew more filament current. The drawings on this page show the original configuration of the 49 as it was in 1929. This is useful information if you are restoring a 49 amplifier to original. The 239-A tubes are thought to have a softer sound and preferred by some people to the 264 tubes.