[Milsurplus] Command set, CCT46104

[D C *Mac* Macdonald]

If I remember correctly, impedance ratio varies
as the SQUARE of the turns ratio.  Therefore,
an 8:1 turns ratio will provide a 64:1 impedance
ratio.  I have no idea as to what the audio out
tube operating impedance is, but it might be
found in an old RCA Receiving Tube Manual.
I wasn't able to find it in mine.

A 6V6 running 180 or 250V on the plate shows
in my old ARRL handbook to have load impedance
of 5.5 k or 5 k, respectively.  If the 12A6 is similar,
the 64:1 ratio would give an approximate output
impedance of roughly 86 Ohms or 78 Ohms.

If only half of the primary were to be used, the
ratio would be 16:1 giving output impedances
of about 344 and 312.5 Ohms.

None of this seems to give a good match, but
the second option would match a  PAIR  of
600 Ohm phones very well.  However, I believe
these radios worked into some sort of intercom
system which would take care of matching any
number of receive headphones.

YRMV.  All of this is pure speculation without any
real justification.  Those theory classes were a
LONG  time ago!!

(;-p)


Mac - K2GKK/5



----Original Message Follows----
From: W7QHO at aol.com
To: WA5CAB at cs.com, Military1944 at aol.com, milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] Command set, CCT46104
Date: Mon, 23 Oct 2006 19:28:35 EDT

In a message dated 10/23/06 9:33:52 AM, WA5CAB at cs.com writes:

 > The parts list in NAVAER 08-5Q-4 does not list the rated output 
transformer
 > impedance (nor did I find it anywhere in the text although I didn't spend 
a
 > lot
 > of time looking).  But it does give the winding data.  Says primary is 
4000
 > turns #40 AWG and secondary is 500 turns #32 AWG.  Primary tapped at 2000
 > turns.  In any case, the 2/42 Final manual does not show a tap on the
 > secondary. 
 >

OK, 4000 turn primary and 500 turn secondary gives an 8:1 turns ratio
transformer.

AN 16-30AEC5-2 gives the same turns ratio for the ARC-5 series receivers and
goes on to list 600 ohm headsets for use with these.   Notes that several of
these headsets may be connected to the same output.

Interesting to note, though, that the SCR-274-N receivers appear to use a 
3:1
transformer to drive low Z (600 ohm?) headsets.

Dennis D. W7QHO
Glendale, CA