[ARC5] Pilot Headset Audio Control In A Typical AN/ARC-5 System

[Michael Hanz]

KK5F has covered the AN/ARC-5 situation beautifully as usual, but I 
think we need to understand that the ARC-5 panoply of nomenclatured 
boxes was an anomaly from a general WWII avionics systems perspective.  
I've often thought that when the ARC-5 design specifications were being 
assembled by the Navy, the Aircraft Radio Corporation must have had a 
whale of a marketing department full court press providing inputs.  The 
list of piece parts to the entire ARC-5 set is enormous.  As Ken 
correctly surmised, the older command set _systems_ had /both/ RF and 
audio gain controls. They just weren't generally produced by the same 
company.  Anything having to do with RF gain was associated with the 
command set provider.  Anything having to do with audio gain was handled 
by the interphone set provider.  Mike made this point, but in the last 
line below refocused on the ARC-5 again, so I thought it might bear a 
little more elaboration to dispel any possible confusion.

If you noodle around 
http://aafradio.org/flightdeck/Interphone_systems.html you will see that 
_every_ station jack box that was a part of any given interphone set had 
an audio gain control on it, even those back in the 1930s.  Some had 
only a limited range of control, but at least it was /something/.  Now, 
there must have been growing dissatisfaction with the limited audio 
volume situation, because by the end of the war there was a trend to add 
a master volume control station to the system, seen at 
http://aafradio.org/flightdeck/box.htm (but retaining the individual 
interphone station box gain controls.)  The Navy RL-24 concept 
introduced a bit more flexibility, and that trend reached a peak in the 
AN/AIC-5 system at the bottom of the interphone web page, where there 
are multiple knobs for every conceivable audio input and output.

To answer ZL1ANM's original question, I occasionally find it useful to 
turn off AVC and ride _both_ RF and audio gain controls when I'm tuning 
around - especially for SSB reception.  So the choice to have both 
capabilities seems like a no brainer to me.

73,
Mike  KC4TOS

On 7/12/2016 3:00 AM, Mike Morrow wrote:
> Ken wrote of the "command set" receivers":
>> Well, depending on the model (early vs late) the AF output is either .5 watts
>> or .75 watts. I have found that if the impedances are properly matched and a
>> speaker is connected, even 0.5 watt output is enough to rattle the windows
> In most of the WWII era, when there was an aircraft interphone system that distributed audio from the command, liaison, compass, and interphone systems to the various call stations, the AF amplifier in the interphone system amplified **only** the carbon mic inputs...no amplification of AF output from command, liaison, or compass systems by the interphone system occurred.  So that 12A6 in a command set receiver could wind up feeding 10 headsets in parallel at various interphone stations of a B-17 or similar.  The ambient noise was very high, yet the 12A6 produced more than enough AF for all those headsets in a combat aircraft that were selected to COMMAND.  The same thing is true of the liaison and compass AF output stages.  As Ken states, AF from any of these aircraft sets operated within specifications should be much more than adequate for any likely hobbyist application.
>>> so they just ran it wide open and vary the the RF gain which determines how
>>> much audio will appear at the detector.  This was a old time legacy design
>>> that was shared by many radios in the pre-war era.
>> Actually, as I understand it, there is an AF gain control in the external controls
>> or rack somewhere. Mike would know. (Either one). Maybe that was on the intercom
>> though.
> The only "command set" system that uses an AF VOLUME control in some installations is the AN/ARC-5, in particular those using the most common receiver control box, the C-38/ARC-5.


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