The information below is from AN 08-10-248, which was superceded by the later AN 16-40RC175-2. The later version records more detail about several versions of the BC-347 amplifier. When I get a chance, I'll try to post it here as well.

The page below is from the Graphic Survey directory series and has an interesting anomaly - the obsolete BC-212 interphone amplifier is pictured,while one of the BC-347-* series nomenclatures is printed for the amplifier in the RC-36. Such errors occurred more often than one would think.

Continuing with the RC-36 section of AN 08-10-248 on the RC-36:

(Parenthetically, the folowing clip shows a way of modifying the schematic above to introduce amplifier gain into the microphone circuit for old carbon mics:)

Now, continuing with the maintenance section from RC-34, as mentioned on page 22 above: