[Milsurplus] Re: [ARC5] Re volume control

[Mike Hanz]

Brian A Clarke wrote:

>Good to cross swords with you again.
>

I didn't consider it crossing swords, Brian - I'm not interested in 
debates.  Just clarifying how the US contingent in the war appears to 
have deployed it as a normal practice.  Other countries no doubt did it 
differently, and as we all know, even different combat units sometimes 
had different approaches.

>From all the manuals and all the installations I've seen, the interphone
>amplifier
>was used as an intercom, rather than as an audio amplifier for the Command
>series receivers. 
>

Agree...but my manuals for the standard series of USAAF interphone 
systems (RC-34, 35, 36, 51,  etc.) all show the 274N command receiver 
outputs eventually connecting to the interphone station boxes, each of 
which has a volume control.  Same with all of the Navy installations, 
though they had a much greater variety of systems to deal with.  It's 
consistent with the few WWII US aircraft I've had the pleasure of 
working in at the Smithsonian, as well.  It's true they didn't always go 
through the interphone amplifier, but I've been careful to talk about 
the complete audio distribution system, not just the amplifier - the 
technical issue was the use of RF gain versus audio volume, IIRC.  But 
then I'm easily and often confused....

>Perhaps the RNZAF and the RAAF developed their own
>practices that differed from their suppliers', but the ARC-5 and SCR-274-N
>manuals I have collected from the USA show no interphone amplifiers in
>aircraft installations.
>

It is correct that the ARA/ATA and 274N manuals are silent on the 
interphone systems they interface.  Not true with the ARC-5 manuals here 
in the library - they show the RL series in the larger systems.  
However, anyone who was trained in avionics at that time would have 
already known that almost none of the manuals for any US aircraft 
radios, not just the command sets, mention the interphone system.  It 
was taken for granted, like propellers or flaps.  Techs were trained 
separately on interphone sets, and in fact all the training books I have 
here, both Navy and AAC/AAF, have separate chapters on them.  Pretty 
interesting reading.  Off the top of my pointy little head, I can think 
of only one relatively common radio whose manual had interphone wiring 
in it other than the ARC-5, and that's the AN/ARC-1 (perhaps the ARC-4 
as well, but I don't have the manual handy and am fuzzy on that aspect 
of it.)

>Re AVC in Command sets - sure the SCR-274-N series used grid
>rectification of the RF voltage from the second IF as feedback applied to
>the RF amplifier and first IF amplifier as the means of achieving AVC,
>while the later ARC-5 actually used a diode for producing a dc bias -
>but it was hardly any more sophisticated. Already by that time [late
>WWII], most British HF sets, AFAIK, had delayed AVC - Murphy,
>Racal, Pye, Plessey, Marconi.
>

Very true.  We Yanks are very backward here in the colonies - it's the 
slow shipping with masts and sails that gets us, though I do hear of a 
new invention called coal and steam that may improve things for us.  
It's amazing that we survived the war at all, especially with that 
klunky BC-348 combined AVC and volume control that RCA came up with.  
Wait!  I remember we had Murphy around a lot.  Though he's getting 
pretty long in the tooth, I still see him just about every day when he 
invokes one of his laws or corollaries!   :-)   Even so, the ARC-5 AVC 
is at least a full range design covering 30-100,000 uvolts (as opposed 
to the step function ARA and 274N design you mentioned above) that works 
as well as the other US aircraft receivers of the period, and it 
functions well enough for my purposes on the ham bands.  The UK sets 
were obviously much better.

>My images of the J-22/ARC-5 in the 1944 NAVAER 08-5Q-95
>manual show no volume control. In fact, none of the J-boxes in this
>manual shows a volume control.
>

Well, only the J-22A and B, C-38, C-39, and C-48 had them...but then, 
they are the primary interface to the crewmen if no interphone system is 
present so it's not particularly surprising.  The J-16 and J-22 non-A/B 
are designed around the C-38 so-called "Pilot's Control Box" so they 
didn't need a volume control.

>I have seen the Station boxes - but they were used with the SCR-522,
>as I recall. I have not seen them specified for use with ARC-5 or
>SCR-274-N. Perhaps there were off-the-book lashups that Americans
>could do because the parts were more readily available.
>

I was using the term station box in its generic sense, as is shown in 
the URL link I included in my last note.  Some folks call them jack 
boxes, and there are a number pictured there - BC-213, BC-366, BC-1366, 
the RL-24 and RL-7 series, even the late war AIC-5 station box, but as 
you can see in the link every one of them has a volume control.

And now I think we have exhausted the useful part of this thread, and 
are in danger of approaching a discussion on the number of angels 
capable of dancing on the head of a pin, so I will turn it over to my 
good friend Cosmoline, who is well known for his exhaustive 
dissertations on the proper cadmium plated screws to use in what 
situations and doesn't like to get involved until we reach that level of 
detail....heh, heh....

Best 73,
Mike