[Milsurplus] Intercom amp (AM-26/AIC)

[Mike Morrow]

>I have here an intercom amp, i think, uses a pair of 12A6 and 12J5 tubes.

It's helpful to any discussion if the equipment nomenclature is cited,
but it's pretty obvious what is being addressed here.

>I picked it up out of the boneyard years ago and thought i might play
>around with it, running a command receiver thru it.  

That's not what the USAAF/USAF did with it.  All WWII-vintage aircraft
interphone amps (including your AM-26/AIC) that I recall do NOT amplify
ANY of the receivers feeding into the system.  That's an assumption that
ham surplus writers have been making for 60 years when they wrote of how
weak the AF output is for various surplus sets such as a BC-348 or a
BC-453 or a BC-433.  Their output, un-amplified, could be selected by
about ten stations simultaneously in many installations.  Must have been
pretty good output!

>I think the knob on the front which is 4 position may be for setting
>the gain.

AM-26 units had a table for setting this switch, or that of the remote
gain switch C-97/AIC (not to be confused with the C-197/ARC-3),
depending on altitude.  Higher altitude had lower air density between
the microphone and the crewman, and required higher gain.  Position 4
sets the highest gain.

Mike / KK5F