With increased mobilization and the need for rapid dissemination of information in today's Army, it becomes absolutely necessary that commanders have a secure means of communications to accomplish this task. Secure telephone is one of these means. One such example is the Digital Secure Voice Terminal (DSVT) KY-68/TSEC. The electronic keying device KYK-13A/TSEC is used to load variables into the KY-68 device. The US Navy is also using the KY-68 as the voice encryption device for some SHF/EHF applications. The KY-68 is the field version of a DSVT while the KY-78 is the office version.

KY-68 (Photo by Austin Mills)
The TSEC/KY-68 shown in a vehicular installation. (Graphic via George Mace)


1) The handset has a 2 position pressure switch that permits (a)  Push-to-talk only in half duplex; send or receive, however not both simultaneously. (b)  Push-to-talk only used in full duplex; send and receive simultaneously.

2) Keypad - Similar in function to standard telephone,  however has additional keys to provide for special functions:

(a)  0-9 numerical data, (RED keys).
(b) FO, F, I, P - Precedence.

FO = Flash Override
F = Flash
I = Immediate
P = Priority

(3)  C - Conference, conference release, and end of dial key.
       R - Used in certain NET radio interface calls.
       O - Used for emergency access.

(4) CRADLE HOOK switch.

A three position switch, that when set enables the following conditions:

(a) Locked on-hook when switch is pushed down and turned to lock position.
(b) On hook state when handset is in the cradle.
(c) Off hook state when handset is removed from the cradle.
(d) Plain text mode when switch is pulled all the way up.

(5) FUNCTION SELECT switch.  -  A five position switch that enables the operator to create the following conditions:

(a)  DSBL - Disables all local operations of the KY-68/TSEC and its extensions; can be used to deny access to extensions; gives master reset to internal circuits (storage position).
(b)  LDU - For loading "U" variable.
(c)  LDX - For loading "X" variable.
(d) OP - Puts KY-68/TSEC into normal operations after initialization is complete.
(e) SVAR - For loading the "S" variable and  permits "S" mode operations.

(6) Audio Volume.

(7) Ring volume.

(8) VARIABLE STORAGE switch. - A three position switch that enables the operator to create the following conditions:

(a)  Zero - Pulled upward and moved to left, zeroes all loaded variables. Plain text can still be operated, (storage position).
(b) Center - Normal operations.
(c)  Load - Momentarily pushed to the right allows operator to load variables.

(9) RING/BUSY indicator.

(10) EXTENSION indicator.

(11) NSW - Non-secure warning indicator.

(a)  Flashes - KY-68/TSEC is operating in a non-secure  mode and is OFF HOOK.
(b)  ON - KY-68/TSEC has not been initialized and is OFF HOOK.

(12) Fill Connector.

(a) Battery compartment/installation date.
(b) Phone number surface. (Use grease pencil only.)


(a)  RCV Terminals.
(b)  Xmit Terminals.
(c)  Gnd Connector.
(d)  Power external supply HYP-71.
(e)  EXT connector - Data devices.


 Initialization (cold start).

 (1)  Required when a zeroed KY-68/TSEC is placed into operations.
 (2)  Handset must be in ON HOOK or HOOK. Switch must be in LOCK position.
 (3)  VARIABLE STORAGE switch is in the normal (CENTER) position.
 (4)  Set FUNCTION switch to DSBL.
 (5)  Insert KYK-13 (electronic fill device) J1 connector into fill connector of KY-68
       or you may use the fill cable. Line up pins and turn connector to lock.
 (6)  Set KYK-13 mode to ON. Do not depress KYK-13 initiate button while unit is in "On Mode".
 (7)  Set KY-68/TSEC FUNCTION SELECT switch to LDU.
 (8)  Select proper KYK-13 channel for U variable. Ring/Busy and NSW  indicators should be lit.
 (9)  Move VARIABLE STORAGE switch to LOAD and HOLD. Annunciator will sound parity tone.
(10)  Release VARIABLE STORAGE switch. It will return to normal (CENTER) position. Annunciator
        will again sound parity indicating U variable is loaded.
(11)  If a 10-second tone or no parity tone is heard, variable is not properly loaded. Return FUNCTION
         SELECT switch to DSBL and repeat loading steps. If variable still does not load, try a new fill
(12)  Load LDX.

 (a) Turn KYK-13 to OFF mode.
 (b) Select channel for X variable on KYK-13.
 (c) Turn KYK-13 to ON mode.
 (d) Set KY-68/TSEC FUNCTION SELECT switch to LDX.
 (e) Move VARIABLE STORAGE switch to LOAD and hold. Annunciator will sound parity tone.
 (f)  Release VARIABLE STORAGE switch. It will return to normal (CENTER). Annunciator will again sound parity tone. X variable is loaded.
(13)  Load SVAR. - Used only for providing additional security between a select group of users on a per
        call basis. Traffic on KY-68/TSEC must be secure end-to-end.


(a) Turn FUNCTION SELECT switch to OP position.
(b) Remove handset and listen for dial tone.  No dial tone will be heard in classroom environment or
      point-to-point operations.
(c) Await ring/answer or busy signal.
(d)  Return handset to cradle when finished.


(a)  +21 to +56 VDC.
(b) Fill Battery BA-1372/U = 6.5 VDC.

Another view of the KY-68 (E-bay photo) 


1) (link now obsolete)


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Apr 19/13