[ARC5] Added 6F6 audio stage...Aircraft Interphones

Sat Oct 20 14:03:31 EDT 2012

Now that excellent explanation makes perfect sense, far better than the 
prior attempts.

Since Ive no experience or interest in aircraft installations I was going by 
some assumptions based upon ship and land equipment. Glad nobody reinvented 
the wheel.

----- Original Message ----- 
From: <WA5CAB at cs.com>
To: <arc5 at mailman.qth.net>
Sent: Saturday, October 20, 2012 1:19 PM
Subject: Re: [ARC5] Added 6F6 audio stage...Aircraft Interphones

> REF: T.O. 08-10-33, Interphone Equipment RC-36 (typical of several
> Equipments using BC-347).
>
> RC-36 consists of Junction Box BC-366 and Interphone Amplifier BC-347.  It
> is designed for Hi-Z audio circuits in 24/28 V aircraft.
>
> BC-366 consists of a rotary switch, multi-pin socket and jack, microphone
> and headset jacks, and terminal strip.  The terminal strip and socket are
> mounted in the base of the box, which is mounted to the aircraft. 
> Connections
> from the terminal strip run to other BC-366's, the BC-347, and the 
> Liaison,
> Command and Compass equipment in the aircraft.  The roitary switch in 
> BC-366
> has five positions, labeled COMP (compass), LIASION, COMMAND, INTER
> (interphone) and CALL.  In the first three positions, BC-347 is 
> disconnected from
> everything and may in fact be removed from its mounting box without
> disturbing anything connected to those switch positions.  With the switch 
> set to
> INTER, one terminal of the amplifier's input transformer primary is 
> connected to
> the MIC jack in that box.  24 VDC is permanently connected through a
> resistor to the other primary terminal.  The output transformer secondary 
> is
> connected to the top of the volume control rheostat of all boxes that are 
> also
> set to INTER.  With the box switch set to CALL (which is a momentary
> position), the input is the same.  The output is connected to the headset 
> jack of all
> boxes in the aircraft and all rheostats are shorted out.  The output
> impedance of the amplifier is such that it overrides any receiver outputs.
>
> So the stamina of a 6F8 (which happens to be a twin triode) isn't at 
> issue.
> The T.O. says that it can handle up to 16 P-18 or HS-23 headsets.
>
> Robert D.
>
> In a message dated 10/20/2012 07:45:24 AM Central Daylight Time,
> geoffrey at jeremy.mv.com writes:
>> ----- Original Message ----- 
>> From: "Mike Morrow" <kk5f at earthlink.net>
>> To: "ARC-5 List" <arc5 at mailman.qth.net>
>> >
>> >>It may not have "amplified" the signal level but like any splitter 
>> >>[sic]
>> >>type unit it provided the same output to up to 10 headphones as if they
>> >>were each connected to a seperate [sic] radio.
>> >
>> >I'm surprised to see such complete nonsense appearing in print on this
>> >forum, save from a very few.
>> >
>> >>In that case it fits its description as an amplifier...
>> >
>> >You can't be serious...now I know you are joking.  Otherwise would admit
>> >to a serious lack of understanding of the fundamentals of physics and
>> >electrical engineering.
>> >
>>
>> I suspect that I have as good as or better understanding of the EE world
>> than you do but Im not obsessive about shoving it in everyones face as
>> you.
>> Typical academic type.
>>
>>
>> >>...and a 6F8 is far from a wimpy tube.
>> >
>> >Nor is the 12A6 or 6K6 or 6V6 in the AF output sections of the various
>> >aircraft receivers.  What's your point?
>> >
>> >The 6F8 in the BC-347-* is only an interphone carbon microphone
>> amplifier.
>> >It is not an amplifier of the outputs of **any** receiver that is
>> >connected
>> >to the interphone system.
>> >
>>
>>
>> I quote from you:
>>
>> >The interphone amp in all common WWII-era aircraft interphones (until 
>> >the
>> >late-war AM-26/AIC, part of AN/AIC-2) did not provide further
>> >amplification
>> >of any receiver's AF output, even one that is connected to ten
>> headphones.
>> >The weak little VT-99 (6F8) of the common RC-36/BC-347-* single-tube
>> >interphone amp was always connected simultaneously to all headsets.
>>
>> And now you say it has nothing to do with headphones.
>>
>> As with many of your posts they seem to be constructed more to confuse
>> rather than educate. In any case a high impedance headphone amplifier is 
>> a
>>
>> natural for the 6F8 if you can actually understand vacuum tube
>> fundamentals.
>>
>>
>>
>> >Have a good day, Carl.  But, just between us friends, why do you
>> **never**
>> >use your **real name** and **call sign** when posting?  I always seem to
>> >have to help you with that!  Never fear, though...I'll always be willing
>> >to help my old friend Carl.
>>
>> Because I signed on from another PC and didnt remember all the setup
>> parameters for OE. Most on here already know who I am so I just left it.
>> Would you like me to sign on with something different so you dont get so
>> itchy twitchy upset? My, my, you are rather high strung.
>>
>> >
>> >73,
>> >Mike / KK5F (Nothing to hide, nothing to deceive!)
>> >And: nothing to offer>
>> >
>
> Robert & Susan Downs - Houston
> wa5cab dot com (Web Store)
> MVPA 9480
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