1A Key--Key Telephone Units

[poplar1]

This is a list of various Key Telephone Units (K.T.U.s) that are used with 1A Key Systems. The most basic system would be two 1A K.T.U.s mounted in a 105-type apparatus box. This would provide holding on two lines.

                           
Code     Unit

      1A     Holding (J53007A)   

      2A     Battery Feed (J53007B)

      3A     Intercommunicating Signaling
                   (J35007C)

      4A      Intercommunicating Automatic
                     Signal (J53007D)
                           
       5A      Auxiliary Hold (J53007E)
   

       6A     Busy Lamp (J53007F)

       7A  Private Line (J53007G)
 

        8A  Blank Mounting Plate with Ter-
                 minal Panel for use as a bridging
                 point in the 105A apparatus box

         9A   Ringing Relay (J53007H) for oper-
                  ating line lamps with or without               
                  a common ringer

Section C53.152 Issue 1, 2-10-39

[poplar1]

-----C53.152 Issue 5, 5-28-48
Code             Function                                         

1A Key Tele-      Holding                                         
phone Unit

2A Key Tele-      Battery feed on intercom-             
phone Unit          municating line, 14-26V.

3A Key Tele-     Intercommunicating code and       
phone Unit          selective ringing                                   

4A Key Tele-     Intercommunicating with             
phone Unit           one-way automatic signal-                   
                            ing. (Replaced by 13B
                            K.T.U.)

5A Key Tele-        Auxilary hold.                           
  phone Unit

6A Key Tele-       Busy lamp. (Replaced by 6B       
  phone Unit          K.T.U.)

6B Key Tele-       Busy lamp and line lamp           
  phone Unit           release.

7A Key Tele-       Private line.                           
  phone Unit

8A Key Tele-      Blank mounting plate with         
  phone Unit         terminal panel. (Replaced             
                           by 8B K.T.U.)                                 

8B Key Tele-      Blank mounting plate for         
  phone Unit         mounting U-type relay and
                           terminal panel for use as
                           bridging point for bridging
                           nine conductors.

9A Key Tele-      Ring-up relay. (Replaced by         
  phone Unit          14A and 15B K.T.U.'s.)                     
                                                                             
10A Key Tele-    Automatic exclusion for use         
  phone Unit         between a principal station
                           and one or more secondary
                           stations.

11A Key Tele-     Ringing lamp for use with
  phone Unit         ringing feeder serving as
                           many as five ringdown
                           private lines.

12A Key Tele-     Dry cell battery feed coil.
  phone Unit

13A Key Tele-     Intercommunicating with
  pone Unit           two-way automatic signal-
                           ing. (Replaced by 13B
                           K.T.U.)

13B Key Tele-    Intercommunicating with
  phone Unit         two-way automatic signal-
                           ing.

14A Key Tele-    Ring-up relay---Manual areas
  phone Unit

15A Key Tele-    Ring-up relay--Dial areas
  phone Unit   (Replaced by 15B K.T.U.)

15B Key Tele-    Ring-up relay---Dial areas
  phone Unit

16A Key Tele-    Common audible signal con-
  phone Unit         trol---Dial areas.

17A Key Tele-    Switching relay.
  phone Unit

18A Key Tele-    Busy lamp and line lamp re-
   phone Unit       lease---Dial lines.

19A Key Tele-    Flashing. (Replaced by 19B
   phone Unit       K.T.U.)

19B Key Tele-    Flashing.
   phone Unit

20A Key Tele-    Common audible signal con-
   phone Unit         trol---Manual areas.

21A Key Tele-    Fuse block unit for six bat-
   phone Unit         tery feed fuses.

22A Key Tele-    Resistance units for lamp
   phone Unit        leads of illuminated sets.
                           8-cell battery supply.

22B Key Tele-    Same as above but for 9-cell
  phone Unit        battery supply.

22C Key Tele-    Same as above but for 10-
  phone Unit         cell battery supply.

22D Key Tele-    Same as above but for 11,
   phone Unit        12 or 13-cell battery supply.

22E Key Tele-    Same as above but for 23 or
   phone Unit        24-cell battery supply.

50A-26 Key       Metal apparatus cabinet,
  Telephone           Olive Green finish, com-
   Unit                   pletely wired and equipped
                            with apparatus for two cen-
                            tral office or P.B.X. lines.
                            Provides flashing line lamp
                            with automatic timing out
                            feature, busy lamp, hold-
                            ing, intercommunicating
                            when desired.

50A-27 Key           Same as 50A-26, but Walnut
   Telephone             finish.
   Unit

50B-26 Key           Metal apparatus cabinet,
   Telephone             Olive Green finish,
   Unit                      equipped and wired for 3
                               central office or P.B.X.
                               lines. Functions same as
                               50A-26.

50B-27 Key          Same as 50B-26, but Wal-
   Telephone             nut finish.
   Unit       

50C-26 Key          Metal apparatus cabinet,
   Telephone             Olive Green finish,
   Unit                      equipped and wired for 4
                               central office or P.B.X.
                               lines. Functions same as
                               50A-26.

50C-27 Key          Same as 50B-26, but Wal-
    Telephone             nut finish.
    Unit

52A Key Tele-      A single 19" mounting plate
   phone Unit            on which are mounted and
                               wired the "per line" relay
                               apparatus required to pro-
                               vide flashing line lamp,
                               with automatic timing out
                               feature, busy lamp, holding,
                               etc., on one central office
                               or P.B.X. line.

53A Key Tele-     A single 19" mounting plate
   phone Unit          containing the "per line"
                             relay apparatus which pro-
                             vides flashing line lamp,
                             steady busy lamp, talking
                             battery, nonring-back on
                             hangup on one automatic
                             tie line.

54A Key Tele-    A single 19" mounting plate
   phone Unit         equipped and wired with
                            apparatus to provide flash-
                            ing line lamp, steady busy
                            lamp, talking battery, etc.,
                            on one ringdown tie line.
                           
55A Key Tele-   A single 19" mounting plate
   phone Unit        equipped and wired with
                           apparatus for providing
                           flashing line lamp, steady
                           busy lamp, talking battery,
                           etc., on one station line
                           circuit.

56A Key Tele-   Two 19" mounting plates on
   phone Unit       which are mounted the ap-
                          paratus for an off-premises
                          station and private line.

Reference:
BSP Section C53.152,
Issue 5, 5-28-48                   

[unbeldi]

Here is a picture of a 105A type apparatus box in which the KTUs were mounted.  NOS condition, found a stash of these some time ago.

[unbeldi]

Many 1A key systems used one of the 60xx-series keys with telephone instruments that didn't have built-in keys.
These were described in the catalogs as early as 1935, although the 1A system was developed in 1938 and published in BLR June 1940.

Here is a 6021B:

The 1935 catalog describes these as follows:

The No. 6021 Type Keys are intended for use at subscriber stations with various wiring arrangements. Each key consists of a key unit enclosed in a black finished metal box and is equipped with push buttons and a terminal strip to which the contact springs are strapped for outside connection. Designation card frame is provided above each button.

[unbeldi]

The 1A key system was developed out of the need to eliminate the typical scenario in which a business executive would have several telephone sets lined up on the desk to accept calls coming in on multiple telephone lines. This was possible with just using keys of course, but it became evident that more features were needed than just switching a telephone from one line to another.

The 1A system was limited to only six lines, but provided access to those lines to many stations.
It was a modular system that could be expanded as needed from a single line and a single set. At a minimum, each line required a single KTU module with a line switching relay assembly. Other KTUs provided service features, as listed in Poplar1's presentation of KTUs.

The 1A system initially had only one visual signal, which consisted of a lighted lamp under the transparent push button of a set to indicate that a line was in use. Later a blinking lamp would indicate ringing on a particular line.

In 1952, the 1A system was redesigned creating the 1A1 system, introduced in 1953. Benefits were simpler connections, smaller modules, more line capacity, and better features and signaling.

Some relevant references with historical perspectives (incl. 1A1 and 1A2):
* Bell Laboratory Record, June 1940
* W.F.B. Wood, Key Telephone Systems: The Latest Chapter, Bell Laboratory Record 44, March 1966, pp.85
* S.E. Bush, Advances in the 1A2 Key Telephone System, Bell Laboratory Record, October 1970, pp. 259.

[paul-f]

There's also good background reading on early key equipment in Section VI of the Pacific Tel Sales Manual:
  http://www.telephonecollectors.info/index.php/document-repository/doc_details/12110-pacific-tel-sales-manual-norcal-nevada-ca-1930-1952

[poplar1]

As described in the 1941 Pacific T&T Sales Manual, Part III, Section 5:

"Holding" (optional) required a 1A KTU for each line.

"Busy Lamps" (optional) to show a line in use or on hold required a 6A KTU for each line. [The 6A did not operate to indicate a ringing line.]

"Line lamps" (optional) to show a ringing line required a 9A KTU for each line [later replaced by the 15B].

"Line ringers": the ringer inside the telephone set could be connected to any one line. Additional ringers externally mounted, or in a different sets, also could be connected to any other line(s).

Alternately, "common audible" ringers or buzzers could be used. The same ringer or buzzer, located inside the set, sounded for a call on any of the lines in the group. 

Line lamps were required whenever common audible signaling was used, in order for the user to know which line to answer. They were optional when line ringers were used. In the 4-button 444 and 6-button 464 sets, the lamps were "combined line/busy" or "signal" lamps. In other words, the same lamp was used to indicate busy (in use or on hold) or incoming call.

On incoming calls, the lamps followed the ring cycle (2 seconds on, 4 seconds off for central office calls) and for held calls, the lamps remained steady. There was no difference in the lamp to indicate a held call vs. a line in use.

[Flashing lamps to indicate an incoming call were available later with the 50-series prepackaged KTUs and with the 19A and 19B KTUs.]

[Winking lamps for held calls would be introduced with the next generation of Key Equipment, the 1A1 in 1953.]

From the March, 1966 BLR article:

...This was later modified so the signal lamp at every station would flash (about a half-second on and a half-second off) when the line was ringing. With the 1A1 a third signal was added to indicate a line being held--a winking lamp (off for about one-twentieth of each half second) at every station where the line appeared.
[emphasis added]

[poplar1]

Additional 1A K.T.U.s:

23A  Noise suppression circuit

24A  Telephone set induction coil unit

25B  Automatic cutoff control circuit

26B  Automatic cutoff circuit

27A  Capacitor circuit (4 mf)

28A  Equalizing resistor circuit

29A  Cut-through relay

30A  Time-out circuit

31A  Battery feed relay

32A  Equalizer unit

33A  Wink circuit  (used with 17B KTU)

51A  CO or PBX line equipment for 2 lines

57A  1 dial-selective signaling intercom (1 per 9 stations)

Reference:
Section C71.331 Issue 1, Dec., 1957, 1A and 1A1 Key Telephone Systems, Identification

http://etler.com/docs/BSP/C/C71.331_I1.pdf

[poplar1]

Additional 1A KTU:

34A  Make busy circuit

Ref: Section C71.331 Issue 3, November, 1961

http://etler.com/docs/BSP/C/C71.331_I3.pdf

Index:

http://etler.com/docs/BSP/C/

[Babybearjs]

Thank you for the posting... the info is wonderful...