[ARC5] Nomenclature Taxonomy - AN/ART-13B

[Mike Morrow]

Robert wrote:

>In the case of T-412/ART-13B, however, there was a significant difference 
>in capability (the crystal oscillator).  So not only the component 
>nomenclature but also the set nomenclature was changed or incremented.

There is *no* difference in the T-47A/ART-13 with CDA-T oscillator and the
T-412/ART-13B other than:

(1)  The T-412/ART-13B has an "EXTENDED LOW FREQUENCY" switch on the front
     to allow crystal operation in the CDA-T as low as 1670 kHz.  That
     switch, "second S117", adds C151 in the plate LC circuit of V102.  But,
     S117 is a careless error.  The "first S117" is the dynamotor control
     power interlock switch to top cover removal that was added to the
     T-47A/ART-13.  It was apparently overlooked when C151 was added to
     make the T-412.
(2)  Although manuals refer to the T-412/ART-13B as a modification of the
     T-47A/ART-13, many T-412/ART-13B units were modified USN T-47/ART-13
     or ATC or ATC-1 units which had neither the "first S117" dynamotor control
     power switch, nor the vernier scale on VFO dial B that allowed dial
     settings at 0.1 of each minor dial division.  Those were the main changes
     between the USN T-47 and the USAAF T-47A.  However, sometimes one can
     find T-412/ART-13B units that are modifications of USN ATC or T-47 units
     that had been upgraded to have the same characteristics as the T-47A. 

>Plus I have to add that a T-47A with an installed CDA-T is not a DOD or 
>USAF modified unit.  USAF modified units got a T-412 nameplate.   Those units 
>without the T-412 nameplate were done by a contractor for Pan American or 
>done by some other non-DOD activity (including hams with the mod kit).

USAF modified units got a T-412 nameplate *only* if they had the EXTENDED LOW
FREQUENCY circuitry in addition to the CDA-T.  There are no T-412 units that
lack this switch.

The USAF T.O. 12R2-2ART13-1 (15DEC56) defines the AN/ART-13B as T-47A with CDA-T,
and does not list the T-412.  The USAF T.O. 12R2-2ART13-2 (30MAR56) also defines
the AN/ART-13B as T-47A with CDA-T, but does list the T-412 and address the
EXTENDED LOW FREQUENCY switch. (http://bama.edebris.com/manuals/military/an-art13/ )
The T-47A/ART-13 with CDA-T without the "second S117" EXTENDED LOW FREQUENCY switch
is an AN/ART-13B without the change of external nomenclature that was done for the
T-412 units with that switch.  These were military units, not post-WWII surplus
or commercial 17H-2 units used by the airlines.

The only thing that the T-412/ART-13B tag guarantees is the presence of that
second S117 and C151, along with the CDA-T oscillator.  The T-412 can be a
modified USAF T-47A, or a modified USN T-47 or ATC in several variations.

Mike / KK5F