[Milsurplus] Command set, CCT46104

[Mike Morrow]

Ben wrote:

>Just received a 1.5-3Mhz comand set, the ARA unit. 
> 
>Looking at the generic command rx circuit the audio o/p transformer is 600  
>or 8k o/p. This one seems much lower imp though, using a hi to lo z  
>transformer audio is low, using a 15 to 3 ohm transformer the audio is
>far  louder.  Internal transformer is orig. 
> 
>So, Q, whats the actual af o/p imp of this set ?

The audio output transformer in an ARA set is about 500 to 600 ohms, although the parts list in the ARA/ATA manual does not actually state the AC impedances for which the transformer is designed.  The same applies to the the transmitter sidetone audio output of the ATA modulator.  This is the major electrical variance of the USN ARA/ATA gear compared to the almost electrically identical USAAF SCR-274-N gear.  The SCR-274-N gear will have either a hi-z output only (-A suffix receivers and modulators) or an internally connected hi-z or lo-z tap (-B suffix units).  There will normally be a decal on the outside stating that the selectable impedance units have been connected for low impedance output.  

Thus, there are three distinct transformer part numbers:  One for the ARA/ATA, and two for the different SCR-274-N variations.

The USN seems to have always used low impedance for their headsets.  The USAAF began WWII using hi-z headsets like the HS-23, but ultimately converted to low-z headsets like the HS-33.

Mike / KK5F