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

[WA5CAB at cs.com]

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