[Milsurplus] FWIW: "Command Set" Receiver Connections To Adapter Panels and Other Information

[Mike Morrow]

"Command Set" Receiver Connections To Adapter Panels And Miscellaneous Accessories

I.  Front Panel Adapter Panels

Adapter panels engage receiver front connector J-1.  NOTE differences for pin 4 on AN/ARC-5 and pin 8 on SCR-274-N receivers.

Pin                 Function
  1      RF Gain Potentiometer, linear 50 kohm to ground
  2      Ground
  3      No connection
  4      ARA and SCR-274-N:  AF Output Transformer Secondary
          R-23*, R-24/ARC-5:  Low level AF from 12A6 cathode **
          R-25, R-26, R-27/ARC-5:  No connection
  5      Ground to shut off CW oscillator
  6      +24vdc to receiver stages
  7      +24vdc from pin 6 of rear connector J-3
  8      ARA and AN/ARC-5:  HV from pin 7 of rear connector J-3
          SCR-274-N except BC-946-B:  No connection
          SCR-274-N BC-946-B:  HV from pin 7 of rear connector J-3 ***

A.  Remote Control Adapter Panel

ARA:  CBY- or CCT-49107
SCR-274-N:  FT-230-A
AN/ARC-5:  MX-21/ARC-5

- Supplied with all receivers except broadcast band models.
- Connects +24vdc pin 7 to pin 6 on receiver connector J-1.
- Connector on most FT-230-A units has electrical connection only for pin 6 and 7.
- All three versions are interchangeable.

B.  DC Power Adapter Panel

ARA:  CBY- or CCT-62036
SCR-274-N:  FT-310-A (used only with BC-946-B)
AN/ARC-5:  MX-20/ARC-5

- Supplied with broadcast band models to provide LV and HV to VHF Homing Adapter ZB-* or AN/ARR-1.
- Usable with other non-SCR-274-N receivers to supply LV and HV power to receiver tuning alignment equipment (LM-*, O-4/ARC-5).  No SCR-274-N receiver except BC-946-B supplies HV at J-1.
- All three versions are interchangeable.

C.  ILS Audio Adapter Panel

ARA:  None
SCR-274-N:  None
AN/ARC-5:  MX-19/ARC-5

- Connects receiver as localizer to AN/ARN-9 Air-Track ILS.
- Connects to filtered 90 and 150 Hz AF from the 12A6 cathode circuit.
- Contains a relay controlled by AN/ARN-9 that shuts off CW oscillator and sets maximum RF gain.
- Used with R-23*, R-24/ARC-5 only.
- AN/ARN-9 Air-Track ILS was abandoned by USN in 1944 for the superior USAAF SCS-51 ILS, which used RC-103-* (BC-773) VHF localizer and AN/ARN-5* UHF glide path receivers.

D.  Local Control Adapter Panel

ARA:  None  (CBY-23154 supplied with RAT, RAT-1, RAV will work)
SCR-274-N:  FT-260-A
AN/ARC-5:  C-24/ARC-5

- Provides RF Gain control and power switch that selects CW or MCW operation.
- Provides NO AF jacks.  Headphones connect locally to jacks on mounting rack.
- A receiver with local control adapter installed requires an LV power connecting plug be installed in the rack connector that normally goes to a remote control.  The plug connects pin 1 to pin 6 to provide LV power to the receiver.
    SCR-274-N:  PL-192
    AN/ARC-5:  MX-2/ARR-2 with connection from pin 2 to pin 8 lifted. ****
- All three versions are interchangeable.

* All version letters
** This AF is filtered for 90 and 150 Hz from 12A6 cathode.  It is used by ILS audio adapter panel MX-19/ARC-5 to supply localizer receiver AF to the AN/ARN-9 Air Track ILS.
*** BC-946-B is always supplied with FT-310-A power adapter panel to supply power to an AN/ARR-1 VHF "ZB" Homing Adapter.
**** The pin 2 to pin 8 connection sets the installed receiver's AF to audio bus B.  MX-2/ARR-2 was required when an AN/ARR-2 receiver was installed in single-receiver rack MT-7/ARR-2.  That rack has no audio bus selector switch.  MT-7A/ARR-2 added such a switch.



II.  Local Tuning Controls

A.  Front Panel Spline

ARA:  A.R.C. 6743
SCR-274-N:  A.R.C. 6743 or MC-237
AN/ARC-5:  A.R.C. 6743

B.  Lock-Tuned Receiver Tuning Key

ARA:  None
SCR-274-N:  None
AN/ARC-5:  A.R.C. 9554

- Threaded base under the AN/ARC-5 tube cover store the brass-colored tuning key A.R.C. 9554.
- The key is supplied with every R-25, R-26, R-27/ARC-5 communications receiver.  These are frequency-stabilized as indicated by a yellow 'S in a circle' paint stamp above the tuning control and a small metal plate to record the receiver's preset frequency.  These improved receivers may be used with no remote
tuning control.  Pre-flight frequency alignment would be made with a signal source while tuning with the receiver's tuning key.  After alignment the tuning key would be removed, reversed, and tightened over the spline tuning port.  The receiver is now lock tuned.
- R-23* and R-24/ARC-5 navigation receivers were never lock tuned.  They required use of a tunable remote control like C-26 or C-125/ARC-5.  These receivers neither use nor require the frequency stability modifications.  They are usually NOT supplied with the A.R.C. 9554 under the tube cover.
- The A.R.C. 9554 tuning key was NOT intended to be the tuning control for a locally-controlled receiver.  The A.R.C. 6743 is the ONLY option.

NOTE:  All AN/ARC-5 receivers have a second storage fixture under the tube cover to store a small tuning dial for the C-26 and C-125/ARC-5 remote tuning controls.  Every AN/ARC-5 receiver was supplied with the appropriate dial stored under the tube cover  These dials are designated, but not marked:

ID-25/ARC-5     0.19 to 0.56 MHz
ID-26/ARC-5     0.54 to 1.50 MHz
ID-27/ARC-5     1.50 to 3.00 MHz
ID-28/ARC-5     3.00 to 6.00 MHz
ID-29/ARC-5     6.00 to 9.10 MHz


III.  Navigation Receiver ANT-LOOP Switch Controls

A.  R-23* and R-24/ARC-5 navigation receivers restored the LOOP terminal posts and switch of their 1940 RAV grandparents CBY-46102 and CBY-46103, but which were removed from their 1941 ARA parents CBY-46129 and CBY-46145 and uncles BC-453-* and BC-946-B.

1.  LOOP-ANT Switch Local Control - A.R.C. 7491
2.  LOOP-ANT Switch Remote Control - C-25/ARC-5

Either of these is extremely rare.  The A.R.C. 6743 local tuning control fits in place of the A.R.C. 7491.

Mike / KK5F