Manual / Guide · 1959

AE Training Bulletin 818: P-A-X's with P-A-B-X Appendix

Private automatic exchanges and PABXs: the system-level guide for a small home PBX.

Author: Automatic Electric Co.
Year: 1959
Type: Manual / Guide
Credit: Telephone Collectors International (TCI) Library, telephonecollectors.info (retrieved via Internet Archive Wayback Machine)

CONTENTS PART I Page 1. INTRODUCTION . 1 AUXILIARY SERVICES 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.1 2 2.13 2.14 3. . . 3 CodeCall . Conference C a l l s D i r e c t Line S e r v i c e Dictating Service . Type 11 Executive Quick-Call Service (Optional Speakerphone), Executive Right-of- \Nay Service Executive Cut-in Service P-A-X F i r e A l a r m Service . Monitoring S e r v i c e Pick-up S e r v i c e SecretarialAnswerilngService Voice Paging Service Toll R e s t r i c t i o n Service Night Answer and T r a n s f e r Service . . . . . . P-A-X SYSTEMS 3.1 3.2 3.3 3.4 3.5 3.6 . 3 3 3 3 3 4 a 4 4 4 5 5 5 5 5 5 . Types 32A1 and 32A321 P-A-X Switchboards Type 32A31 P-A-X Switchboard Type 32A38 P-A-X "Common-talk'' Switchboard Types 47A and 47B :P-A-X Switchboards TheTypes25and50P-A-XSystems. Type 75 P-A-X Switchboard . . 5 . . 7 . 8 9 . 10 . 12 PART I1 1. INTRODUCTION 2. P-A-B-X 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 SYSTEMS . 15 . . 15 Types 32A1, 32A21, 32A31 P-A-X S y s t e m s (Converted) T y p e s 25B, 50B, 75B P-A-B-X Switchboards Type 85 P-A-B-X Switchboard . Type 95 P-A-B-X Switchboard . Type 33A6A P-A-B-.X Switchboard Type 33A35 P-A-B-:Y Attendant Cabinet Type 33A19 P-A-B-:Y Attendant Cabinet . Type 51 P-A-B-X Attendant Cabinet . . . . . 15 . 16 . 18 . 19 . 21 . 21 . 21 . 17 An A. E. C:o. P-A-B-X system (type 75). EXCHANGES PRIVATE AND PRIVATE AUTONIATIC BRANCH EXCHANGES PART I 1. INTRODUCTION T h e P r i v a t e Automatic Exchange, abbreviated P-A-X, is a n automatic intra-office 'telephone s y s t e m which s e r v e s b u s i n e s s houses and institutions. The P-A-X is composed of standard switching equipment designed to fit the specific r e q u i r e m e n t s of any e n t e r p r i s e . P-A-:X switchb o a r d s a r e produced in a number of standard types and s i z e s ranging f r o m t h r e e telephones to any number desired. And once installed, initial switchboard capacity m a y be i n c r e a s e d . Planned expansion r e q u i r e m e n t s can e a s i l y be m e t with Automatic E l e c t r i c Company's flexible P-A-X s y s t e m s . The P-A-X, a s a n isolated, local s y s t e m , has a number of advantages f r o m the standpoint of both s e r v i c e and cost. F i r s t , i t gives "double track" telephone s e r v i c e . An inquiry received on a c a l l made from a city exchange telephone m a y be investigated privately over the P-A-X while the city call is waiting. Automatic local communication a l s o s p e e d s i n t e r i o r information flow and eliminates c a l l s handled locally by a switchboard attendant. Switching equipment employed in the P-A-X s y s t e m s vary with the specific demands and r e q u i r e m e n t s of the u s e r e n t e r p r i s e . In s y s t e m s with plunger lineswitches, one switch is associated with each line. They function, p r i m a r i l y , to connect a calling line to a n i d l e connector. Essential to plunger lineswitchcontrol is the masterswitch. This control switch keeps up to 100 plunger lineswitches in p r o p e r posit i o n It o p e r a t e s to a s s u r e that a group of plunger lineswitches a r e connected to a single f r e e outgoing c o n n e c t o r Generally, each plunger lineswitch group consists of 25 to 100 lineswitches p e r masterswitch. E a c h lineswitch a l s o h a s a c c e s s thru a m a s t e r s w i t c h to a maximum of 10 outgoing trunks. The m a s terswitch s t e p s a l l idle plunger lineswitches in a group to a position opposite a n available trunk. This p r e s e l e c t s y s t e m i s then in position for the next s u b s c r i b e r call. F i g u r e 1 i l l u s t r a t e s a typical plunger lineswitch circuit. . . In s o m e s y s t e m s the r o t a r y switch r e p l a c e s the plunger lineswitch. Basically, the r o t a r y PLUNGER' LINESWITC:H CALLING STATION CALLED STATION Fiewe I . T).pical plz~?zgerlitzeszc3itc/~ civcrcit as llscrl rtitlz the T j p c 25 P-A-X Sztitcitbonrd. ' - i)lNG a s a linefinder. In this c a s e the switch becomes a non-numerical switch in connecting a calling s u b s c r i b e r ' s line thru a trunk link to a connector. The Strowger linefinder c o m e s in two capacity s i z e s - 100 and 200 lines. The 200line linefinder is s o a r r a n g e d that i t s e l e c t s any one of two groups of 100 bank contacts. In the. 100 -line Strowger f i n d e r s y s t e m , the mechanism s e l e c t s a line f r o m one group of 100 bank contacts. T h i s s y s t e m is found, f o r example, in the Type 75 P-A-X Switchboard. Figure 3 details the circuit. REMAINING TELEPHONES I I I I ROTARY FINDERS ROTARY ICONNECTORS Figure 2. Rotary lineJzfilzdersand corrnectous as employed i)z tile Type 32.41 Su~itchboa~*d. lineswitch s e r v e s a s a single -motion, nonn u m e r i c a 1 switching device for connecting a calling line. to a n idle trunk. The operation of t h i s switch is entirely automatic. When a c a l l e r picks-up his t e 1 e p h o n e handset, the r o t a r y switch is activated. In addition, no m a s t e r s w i t c h is r e q u i r e d . The r o t a r y line finder is shown in figure 2 . The switch. connects a "seized" s u b s c r i b e r ' s line to a n idle trunk. At the other end of the line, a r o t a r y stepping switch s e r v e s a s a connector. T h i s a r r a n g e m e n t is used in the Type 32A1 P-A-X Switchboard. Other s y s t e m s using r o t a r y linefinders substitute two-motion, numerical Strowger conn e c t o r switches. The Strowger s w i t c h r e p l a c e s the one-motion r o t a r y s t e p p i n g switch f o r connecting a link to a called party. This type is used with the Type 32A31 Switchboard. The Strowger, two-motion switch can a l s o s e r v e In actual operation, a distributor switch common to all linefinders in a group d e t e r m i n e s w h i c h idle finder w i 11 s e r v e the next call. When a s u b s c r i b e r picks up his telephone handset, the line equipment busies his line to a l l other c a l l e r s , activates the group r e l a y s , and m a r k s h i s line contacts on a l l the linefinder banks. The linefinder then s e a r c h e s out the marked line and puts t h r u a connection to a connector. Once this c i r c u i t is established, dial pulsing m a y begin. There a r e two g e n e r a l classifications of private automatic exchanges. The "stock board" type denotes a switchboard that is a "standard item." It h a s specific wiring and equipment a r r a n g e m e n t s and is readily available when required. It is designed to m e e t n o r m a l u s e r requirements. A "stock board" then, is a p r i vate a u t o m a t i c exchange that is wired and equipped a t the factory in a "standard" manner,. The second classification of private automatic exchanges is the "specially engineered" unit. This type unit is non-standard in s i z e and is available f o r those u s e r s who have special c a p a c i t y and s e r v i c e r e q u i r e m e n t s . The "specially engineered" u n i t is custom built for abnormal u s e r needs. CONN. CALLING STATION :1 e i l Figire 3. Strolcrgcr 100-line linefinde,- as tiscd in the Type 75 P--4-X Src~itcl~boat~d. CALLED STATION 2. AUXILIARY SERVICES Automatic Electric Company provi~desa multitude of a u x i l i a r y s e r v i c e s for use w i t h P-A-X and P-A-B-X equipment. This section will describe several of these s e r v i c e s in detail; other services will be outlined briefly f o r r e a d e r acquaintance. F u r t h e r i n f o r m a t i o n concerning any of A. E. Co.'s auxi:liary s e r v i c e s will be furnished on request. s t a t i o n may originate a conference call by dialing the prescribed progressive conference number. The l a s t two digits of each individual station a r e then dialed. As each party answers, the switch mechanism r e l e a s e s and allows the originator to dial other stations. If a dialed party does not answer, the originator momentarily hangs-up before dialing the next number. T h i s auxiliary service is available only for 48-volt switchboards. I t c a n s e r v e up to 20 stations. 2.1 Code Call The function of code call service is the paging o r signaling of individuals when they a r e not directly accessible by telephone. Units providing a maximum of 10 one-digit codes o r a m a x i m u m of 125 three-digit codebs a r e supplied by A. E. Co. Code call equipment is operated by dialing the c o d e call prefix number. This connects the paging p a r t y to code call equipm.ent. If the equipment is idle, the calling party dials the assigned code n u m b e r of the party sought. The called 'party answers by dialing the a s s i g n e d code "answering" number. The two parties a r e then connected via a private P-A-X c o n n e c t i o n . If the called party cannot be reached, the e q u i p m e n t is disconnected by either (1) replacing the handset, o r (2) using a preset automatic cut-off. If desired, divisional code c a l l equipment may be installed and arranged to sound in different p 1a n t a r e a s by dialing different code a c c e s s numbers. Each assigned number automatically sounds a n "annunciator" system in the a r e a where the individual is likely to be. 2.2.3 "Meet-Me" conference. This auxiliary service derives i t s name f r o m the prearranged conference time and date. At the prescribed time, each party in the conference group dials the conference n u m b e r . All P-A-x stations can have access to the conference circuit. In contrast to the other conference s y s t e m s , the "Meet-Me" conference allows p a r t i e s to ent e r , leave, and re-enter the circuit a s long a s there a r e sufficient selectors o r connectors. 2.3 Direct Line Service Many times in a P-A-X s y s t e m a majority of individual telephone calls go from one particu l a r s t a t i o n to another. To avoid repeated dialing thru P-A-X equipment, the d i r e c t line service can be provided in addition to regular equipment. In this system, ringing of the other particular line is accomplished b y m e r e l y l i f t ing the handset. The P-A-X equipment, ~ t s e l f , is used only for battery and ringing current. 2.4 Dictating Service If a number of persons need a c c e s s . t o a dictating machine, it may be convenient to have the machine P-A-X connected. Anyone d e s i r ing dictation service dials the machine a c c e s s n u m b e r . In o n e system the m a c h i n e is arranged to s t a r t recording by pressing and holding a b u t t o n on t h e telephone handset. Another system uses a machine s t a r t number. F o r a correction o r playback, additional numb e r s a r e dialed. - 2.2 Conference Calls Conference equipment p e r m i t s a desirednumb e r of telephones to be connected to a common line. Conferring parties may simultaneously s p e a k and listen. T h r e e types of conference arrangements a r e available. . 2.2.1 Group c o n f e r e n c e Group conference equipment allows t h e simultaneous; signaling of ten predetermined stations in a fixed conference group. To originate a conference call, o n e member of the f i x e d group ti i a 1 s the assigned number of the conference c:onnector. The group conference unit i s "seized," and automatically rings all lines assigned to the group. Stations may withdraw from the conference a t any time. But once a party withdraws, he cannot r e t u r n to the conference. T h e l a s t party hanging up in the conference group idles the unit. 2 - 2 . 2 Progressive conference. Progressive conference equipment allows t h e alddition of stations to a conference circuit. Ariy P-A-X Access to a number of dictating machines is possible w i t h A. E. Co's. dictating service. T y p e s 50 and 75 P-A-X s y s t e m s a r e especially applicable to the multi-machine dictating service. 2.5 Type 11 E x e c u t i v e Quick-Call Service (Optional Speakerphone) T h e Type 11 e x e c u t i v e quick-call system maintains direct line communication between a n executive and up to 20 individual private 1 o c a 1 telephones. S i n c e direct line service eliminates dialing, executive quick-call s e r v ice instantly connects the executive to those individuals most frequently called. The T y p e 11 quick-call s y s t e m gives one e x e c u t i v e in an o r g a n i z a t i o n m a s t e r s t a t i o n control of all initiated d i r e c t 1 i n e calls. He m a y selectively call any of 20 individual telephone stations designated a s "direct line." These 20 stations, however, cannot call the executive except thru the P-A-X b<ydialing i n the usual manner. The executive may call, in addition, any of the d i r e c t line stations by P-A-X dialing. The executive reaches a direct line station by using manual push keys located on the masterstation control u n i t (quick-call cabinet). To r e a c h a d i r e c t line s t a t i o n , the executive s e l e c t s and then p r e s s e s a cabinet push key. He r i n g s the c a 11e d station's telephone by picking-up his telephone handset o r pressing the ON button of h i s optional Speakerphone. If the called station's telephone t e s t s "busy," another key on the cabinet will place a distinctive "tone" s i g n a 1 in the background of the called p a r t y ' s conversation. O r , if the executive chooses, the handset may be left off the hook until the call is completed. He will be automatically connected to the called party i m m e d i a t e l y after t h e conversation. A n optional feature allows still another choice in quick-call service. By pressing another push key, the executive can "cut-in" on the busy line. F o r the convenience of "hands free" operation, the executive quick-call s y s t e m can be used with the Type 88T Speakerphone. If the Speakerphone is used, the calling party's voice is heard thru a s m a l l speaker next to the telephone. The executive's voice is picked-up by a tiny microphone located in the baste of the telephone. The handset is not t a k e n off the hook. In addition, loudspeaker operation per m i t s a d i r e c t line party to talk freely in group conversation with m o r e than one person in the executive's office. 2.6 Executive Right-of-way Service This auxiliary service gives a n executive the convenience of a separate, private coiiversat i o n channel. It e n a b l e s him to j o i n any established conversation d e s p i t e a "busy" signal. A warning tone m a y a l s o be applied f o r informing the conversing parties that an executive wants to cut-in. A n e x e c u t i v e reaches a busy party thru a r e s e r v e d connector. Normally, the executive's telephone is equipped w i t h two-line pick-up keys. One key connects to the regular P-A-X equipment and the other to the right-of-way c o n n e c t o r . To cut in the executive p r e s s e s the associated c o n n e c t o r key and dials the number. He is then directly connected to one of the c o n v e r s i n g parties. When the other party drops out, the executive and remaining party a r e connected via the standard P-A-X connector. 2.7 Executive Cut-in Service E x e c u t i v e cut-in service incorporates the s a m e ' general features a s the executive rightof-way service. This system, however, does not provide a separate conversation channel. Executive cut-in service employs s t a n d a r d telephones with a grounding push button and is used only with the Types 47A and 47B P-A-X Switchboards. In operating the cut-in service, the executive p r e s s e s a grounding push button on the telephone. His telephone immediately connects to the wanted party's telephone. The called party and the executive r e m a i n connected when the unwanted party hangs-up. 2.8 P-A-X F i r e Alarm Service P-A-X t e l e p h o n e s can be used alone a s a n emergency a l a r m . But the more elaborate f i r e a l a r m reporting s y s t e m s require auxiliary equipment. One f i r e a l a r m reporting system p r o v i d e s s e r v i c e for a maximum of 90 stations. In the e v e n t of fire, the reporting station dials the assigned P-A-X number a n d is immediately connected to f i r e a l a r m equipment. The f i r e a l a r m equipment identifies the location of the reporting station and sends a signal to a cent r a l fire office. At the s a m e time, the f i r e m a r s h a l is notified and a connection is placed and locked between his telephone and that of the reporting party. This insures that a direct connection can be maintained with the reporting party. 2.9 Monitoring Service When t e 1 e p h o n e supervision is necessary, Automatic Electric Company's m o n i t o r i n g service allows listening-in on conversations. Signal lamps, associated with individual talking paths, a r e part of a monitor panel. T h e person monitoring a call can listen-in without disturbing the ,conversation. He may a l s o engage in conversation with the talking parties. Monitoring service involves the use of a port7 able handset w i t h a cord and telephone -type plug. A cut-in button on the handset cuts the transmitter in and out of the monitor panel for conversing with talking P-A-X parties. A p e r son monitoring a circuit i n s e r t s the plug-ended cord into the telephone jack just u n d e r the glowing panel light. If he wishes to converse, he p r e s s e s the transmitter operate button on the handset and interrupts the conversation. 2 -10 Pick-up Service 2.1 3 Toll Restriction Service P i c k - u p s e r v i c e p e r m i t s a n individual to answer c a l l s on his telephone b y dialing a special number f r o m any other telephone in the system. F o r those away from thieir desks much of the time, this is a n important service. Toll restriction service applies to those s i t uations w h e r e some norr-restricted stations make, receive and t r a n s f e r central office calls, but cannot make toll c a l l s t o the public exchange. If a restricted toll number is dialed, all digits a r e absorbed by the r e s t r i c t e d s e r v i c e adaptor. The number will not be t r a n s mitted to the central office. The trunk r e l e a s e s after absorption o f the r e s t r i c t e d digits and makes the trunk available to other calls. 2.1 1 Secretarial Answering Service Several arrangements may be made whereby a s e c r e t a r y has facilities for answering and transferring c a l l s made to a department group. The s e c r e t a r i a l answering service unit can be obtained in s i x o r ten-line s i z e s with a signal lamp and three-position key for each line. When a c a l l comes in on a line, a corresponding lamp flashes. If the called party is away f r o m his telephone, the s e c r e t a r y pushes up the line key to answer the call. By moving the key to the "hold" position, the s e c r e t a r y can hold the line while answering other c a l l s . If third party information is needed, the secr e t a r y turns a n idle line key to the answer position and dials the number. After the information is obtained, the third pal-ty key is returned to normal and the "hold" line is r e turned to the answer position. Only one line can be qonnected to the s e c r e t a r y ' s telephone a t one t i m e . However, s e v e r a l c a l . 1 ~can be held simultaneously. 2.12 Voice Paging Service Automatic Electric Company offers two additional circuit arrangements for toll r e s t r i c tion. One circuit is used to r e s t r i c t stations completely from the toll operator o r automatic ticketing equipment. Another circuit r e s t r i c t s certain stations from "long haul" toll calls, but allows stations to r e a c h "short haul" toll a r e a thru ticketing equipment. 2.14 Night Answer and T r a n s f e r Service F o r night answer service, s e v e r a l lines in a P-A-B-X a r e tied to central office equipment. T h e s e lines connect central office trunks to night answer j a c k s on the attendant cabinet. The night answer jacks, in turn, connect to a night answer and transfer unit. A c a l l received during the night s e i z e s the night answer and t r a n s f e r unit. Automatic seizure r i n g s the night bell, o r o p e r a t e s a code call machine. Any local telephone in the P-A-B-X c a n answer the incoming c a 11 by dialing a predetermined night "answer' ' number. Voice paging is s i m i l a r to the c o d e calling service described in section 2 .l. Here, howe v e r , the calling party is connected directly thru the P-A-X to the plant loudspeilker s y s t e m instead of to visual o r audible i2nnunciat o r s . The wanted party is not paged by code in this s y s t e m . If a second party in the local system is wanted, the answering party u s e s another telephone and dials the wanted local number. After the f i r s t party reaches t h e local number, the second party dials a "transfer" number and is connected thru to the incoming call. The f i r s t answering party can then r e t i r e from the circuit. A party wishing to contact another party lifts h i s station handset and dials the designated P-A-X voice "paging" number. If the system is idle, ring-back tone s i g n a 1 s him to begin paging the wanted person. The calling p a r t y pages by speaking directly i n t o his handset. The called party a n s w e r s by dialing a voice paging "answer' ' number. This connects him to the calling p a r t y and disconnects paging equipment. 3. P-A-X SYSTEMS A. E. Co. a l s o offers a n alternative voice paging service. In this system, the party using the paging s e r v i c e hangs up a f t e r tal.king over the speaker s y s t e m The paged party then dials, t h r o u g h regular telephone ecluipment, the P-A-X n u m b e r of the paging party. He does not use a paging "answer" number. . T h i s section and the following s e c t i o n on P-A-B-X systems a r e written to familiarize the telephone man with the m o r e important types of automatic equipment available from A . E . C o . All P-A-X u n i t s will n o t be described. Only the important features of commonly used stock s y s t e m s will be outlined. Addition21 information on any specific P-A-X o r P-A-B-X s y s t e m can be obtained under separate cover. 3.1 Types 32A1 and 32821 P-A-X Switchboards These two P-A-X s y s t e m s a r e s i m i l a r i n performance, functions, and auxiliary services offered. They differ in line capacity artd numb e r of possible simultaneous conver:;ations. The Type 32A1 P-A-X has an "ultimate" line c a p a c i t y of 10 single-party telephones. The switchboard can handle two simultaneous conver sations . The Type 32A21 P-A-X has increased "ultimate'' c a p a c i t y (22 lines) and handles three simultaneous conversations. In both systems, t e 1e p h o n e capacity can be doubled by using two -party lines . Switchboard equipment on the 32A1 an~d32A21 P-A-Xs is v e r y much alike. The 32A1 equipment consists of four 11-point r o t a r y switches and associated relays. Two switches s e r v e a s linefinders and two f u n c t i o n a s connectors. Associated with each line is a relay. One additional r e l a y s e r v e s a l l lines a s a "common" relay. Included in the s w i t c h i n g unit is the ringing equipment. Figure 4 is a photograph of the Type 32A1 P-A-X, and figure 2 illust r a t e s a simplified switching arrangement of the 32A1. T h e Type 32A21 P-A-X also utilizes r o t a r y linefinders and connectors. However, this unit uses s i x 2 5 p o i n t switches f o r operation. Three switches s e r v e a s linefinders and three a s connectors. The Type 32821 h a s 22 line relays, and a u x i 1i a r y and common relays. Figure 2 diagrams the switching circuit. - The ringing arrangements of the s y s t e m s a r e not alike. The Type 32Al uses only a singledigit number f o ;;' single -party ringing o f i t s ten lines. The Type 32A21 has three numbering groups for i t s 22 lines. Because 25-point r o t a r y switches a r e u s e d , numbers 1 to 9, 01 to 09, and 001 to 004 can be assigned to subscriber 1 i n e s . F o r two-party ringing in either of these P-A-X systems, an additional ringing digit is suffixed to the line digit. The suffixed digit applies a long o r s h o r t ring for party-line identification. The r i n g i n g digit must be redialed for each telephone ring. As figure 4 indicates, the lower cabinet section in the Type 32A1 contains all the power supply equipment. Power is s u p p 1i e d to the switching unit by a battery eliminator delivering 24-volts dc, a t 3-amperes. A 12-cell s t o r age battery and a 1-ampere battery charger can also be used. Under certain conditions a 110-volt d-c power supply source may beused a s optional power source equipment. The Type 32A21 P-A-X uses the same power equipment. An all-metal cabinet mounts the switchboard unit and power equipment. When storage batt e r i e s and associated c h a r g e r a r e used in p 1a c e of a battery eliminator, a n additional cabinet unit usually mounts on top of the twocompartment cabinet. The lower portion of the cabinet then houses the storage batteries. L i k e the "32A1", t h e P-A-X T y p e 32A21 houses a l l r e l a y s , ringing equipment, terminal blocks and fuses on mounting bases enclosed within the cabinet. The "32A21" a l s o has two s h o r t angle pieces which serve a s feet for mounting the switchboards independent of 'the cabinet. Figure 4. Type 32-41 P-A-X S~~~itchbonrtl. Auxiliary s e r v i c e s a r e available for both the Type 32Al and Type 32A21. Most of the s e r v ices outlined in section 2 can be used. It should be noted, however, that installation of special equipment may cut-down the number of individual telephone links. Figure 5. Type 32A3I P-A-X S~clitchboard(line-finderside). 3.2 Type 32831 P-A-X Switchboard T h e Type 32A3 1 P-A-X Switchboard has an "ultimate" capacity of 50 lines andpirovisions for seven possible simultaneous conversations. If desired, it m a y be equipped to s e r v e only 30 lines with any number of conversation channels ranging f r o m t h r e e to seven. All internal wiring is in place for future expansion to the maximum 50 telephones. The m e t a 1 switchboard cabinet divides into two horizontal compartment sections. This is s i m i l a r in nature to the previously discussed Type 32A1 and Type 32A21 Switchboai-ds. The u p p e r section c o n t a i n s line and switching equipment. The lower cabinet section houses power equipment. It holds either a 24-volt dc, 3 -ampere battery eliminator, 12 -cell storage batteries with a 1-ampere charger, o r special voltage control equipment. Refer to figure 5 for a linefinder view of the Type 32A31. The talking path is the finder -connector type. The linefinder is a s i x level, 25-point r o t a r y switch. Its wipers a r e s o arranged that during a single revolution, the s w i t c h successfully t e s t s each of the 50-lines in the 32A31 P-A-X Switchboard. The talking circuit 1s completed with a two-motion S t r o w g e r connector (see section 1). Figure 6 depicts a typical 25-point r o t a r y linefinder and 100-line Strowger connector switch circuit. F o r automatic single -party ringing in the Type 32A31 Switchboard, a l l telephones a r e assigned two-digit numbers. They range from 11 to 50 with individual r i n g e r s bridged across; the line. When two stations a r e connected to a common 1 i n e for two-party operation, o n e telephone number is required for each party. -1Yumbers 11 to 50 a r e assigned to one station a.nd numb e r s 61 to 00 a r e assigned to the second line member. Ringers of the f i r s t station a r e connected from o n e side of the line to ground; r i n g e r s of the second s t a t i o n a r e connected f r o m the other side of the line to ground. The switchboard s w i t c h i n g unit consists of a Strowger two-motion switch, a s s o c i a t e d r e l a y s , ringing apparatus and a line terminal block. Two talking leads from each telephone terminate on the terminal block to form a common-talk circuit. Ring leads terminate on the b a n k terminals of the Strowger switch. Although a l l t e l e p h o n e s a r e connected to one common pair of line wires, i t is customary to install t h e s y s t e m with individual wire& for each telephone. T h e s e wires a r e then connected together on a line terminal block a t the switchboard. Figure 7 is a photograph of the Type 32A38 P-A-X Switchboard. 3.3 Type 32A38 P-A-X "Common-talk" Switchboard The mounting equipment includes five vertical r e l a y s t r i p s on whichare mounted the Strowger switch, a l l r e l a y s and ringing equipment. The vertical s t r i p s a r e bolted to c r o s s angles a t the top and bottom of the upper compartment of the two-compartment sheet metal cabinet. Power equipment is located in the lower portion of the cabinet. The Type 32A38 P-A-X S w i t c h b o a . r d is a "common-talk", isolated exchange. It has an "ultimate" capacity of 100 lines. Ordinarily, only one conversation can take place a t a time. T h r e e service types a r e provided. They a r e the (1) fully automatic; (2) automatic m a s t e r s t a t i o n control of regular stations, and (3) automatic master-station control of r e g u 1a r stations with added auxiliary masterstations. The Type 32A38 can also be arranged for auxi l i a r y s e r v i c e s including a s e c r e t service feature. This "common-talk' ' systern is e s pecially designed to meet the service require ments of schools, s m a l l factories and offices where traffic is not heavy. In some instances the telephones of the Type 32A38 a r e not a l l designated "common-talk." A divided arrangement can b e s e t up where one group of telephones is designated "secret service," and a n o t h e r group a s "ordinary service." The s e c r e t service group consists of a maximum of 30 telephones. Any two s t a tions in this group can c a r r y on s e c r e t conversation without being overheard by stations a s s i g n e d to the "ordinary" service group. Other "secret service" s t a t i o n s , however, may intrude on the conversation. Also, a conversation started within the secretgroup automatically "splits" the two groups. This makes it possible for two simultaneous calls with the s e c r e t service arrangement. One call can take place in t h e s e c r e t service group while the second is associated with the ordinary service - When designed for fully-automatic service, the Type 32A38 P-A-X comprises a maximum of 100 telephones c o n n e c t e d to a single twoconductor line. The bell of each telephone is rung over an individual wire when the distant c a l l e r dials the c o r r e c t two-digit num.ber. The bell a t a called station rings only once. To r e ring, the number m u s t be dialed again. In some c a s e s , "busy" lamps a r e provided for observing whether o r not the system is in use. CALLING STATION ROTARY LINEFINDER - . . . :u .. .... . CALLED STATION • LE CONN. NORMAL • Figure 6. Type 32A3I P-A-X Stcfitchboard. Deiilonstrating rota;+.ylinefinder, S t ~ ~ o u g e r cotznector principle. LE o 1 t call each other. This removes traffic f r o m the switchboard and supplies s e c r e t service. No switching equipment is utilized and two calls may be in p r o g r e s s simultaneously (one in the switchboard and one on the direct line). The two stations arranged for direct line service may also be connected to the P-A-X by means of a switching key for both P-A-X and direct line service. Like a l l previously discussed P-A-X switchboards, the 321238 P-A-X is designed to operate from either a 24-volt d-c power supply, a 12-cell 20 a m p . e r e - h o u r battery with a 1-ampere charger, o r o t h e r power sources with proper voltage control. 3.4 Types 47A and 47B P-A-X Switchboards The Types 47A and 47B P-A-X Switchboards a r e identical in switching, line and auxiliary equipment. They differ only in line capacity. The Type 47A P-A-X Switchboard has an ultimate capacity of 20 single-party lines, while the Type 47B P-A-X has a maximum capacity of 40 single-party lines. F o u r simultaneous calls can be attained with the 47A P-A-X; the 47B can have six. Figure 7. Type 32438 P-A-X Switchbowd. group. F o r two simultaneous calls, the s e c r e t s e r v i c e connection must be established prior to the ordinary service group connection. Figu r e 8 demonstrates the T y p e 32A.38 P-A-X with two group s e r v i c e . The Type 32A38 can be provided with an automatic master-station c o n t r o 1 arrangement. Here, one station is assigned a s a "master" o r "controlJ' station. This station i s the only one equipped with a dial for selectivie signaling of a l l other s t a t i o n s in the syst~em.Other "outlying stations" a r e r e s t r i c t e d to calling the m a s t e r station. They cannot dial o r call among themselves. The third Type 32A38 P-A-Xarrangement adds dial equipped stations to the m a s t e r station. These additional stations a r e termed "auxilT h e masterstation o r i a r y masterstations auxiliary m a s t e r s tations can selectively signal any one of the "outlying" stations andalso signal each other. Outlying stations,, however, can still only signal the masterstation. ." If desired, P-A-X telephone capacity can be doubled by arranging for party-line operation. Automatic ringing accompanies single -p a r t y signaling and selective signaling is used for party-line ringing. Figure 9 s h o w s the 47A Switchboard. The switchboard unit includes line r e l a y s (one per line), auxiliary and common relays, ringing equipment, dial and busy relays, terminal blocks and f u s e s . Twenty-five-point rotary stepping switches s e r v e a s b o t h linefinders a n d connectors. The switchboard u n i t s a r e housed in steel cabinets. Front and r e a r doors lift off. All units, including the power supply, a r e mounted on a s e r i e s of plates t h a t a r e bolted to 'the frame. The r o t a r y switch bank, though, is mounted b e t w e e n two horizontal b a r s and bolted to the frame. Figure 2 presents a switching schematic diag r a m of the Type 47A P-A-X. The linefinder principle i s m u c h the s a m e a s with other P-A-X systems discussed in this bulletin, The 25-point r o t a r y linefinder rotates and t e s t s for the calling line when the c a l l e r picks up the handset. The calling line is then connected to another 25-point r o t a r y connector switch. In these type 'P-A-Xs, however, the connector is stepped differently than normal. The 25-point r o t a r y connector switch is designed to receive dial p u l s e s for selective signaling of either party on a two-party line. Direct line s e r v i c e can b e provided for any two stations which have frequent occasion to The f i r s t p . a r t y is assigned a n u m b e r for ringing on one side of the line to ground, and r ORDINARY GROUP I L 1 1 !SECRET-SERVICE GROUP Figure 8. Type 3,2338 P-A-X Su~itchboard. Demonstratillg a system zuith two group services. the second p a r t y ' s number rings from the other side of the line to ground. Selective dial numbering causes selective r i n g i n g of each telephone over a common pair of wires;. Power in the Types 47A and 47B P-.A-Xs i s usually supplied by a 24-volt battery eliminator. If an eliminator is not u s e d , a 12-cell storage battery arrangement can be pllaced at the b o t t o m of the switchboard cabinet. It i s charged by a 3-ampere (type 47A) o r 6 -ampere (type 47B) battery charger located outside the cabinet. 3.5 The Types 25 and 50 P-A-X Systerns The Types 25 and 50 P-A-X systems a r e specially designed to meet expandable telephone n e e d s They a r e characterized by compact sectional d e s i g n and ease of expansion-onlocation. "Stock" installations can be readily supplemented by additional sections. The 25 and 50 P-A-X systems a r e also fully adaptable for use with the auxiliary services described in section 2. The design and functions of the 25 and 50 a r e similar. This section will discuss these similarities along with the distinguishing features of each system. . --. & Figure 9 . Type 47A P-A-X Szcdtcfiboal-d. Both the 25 and 50 P-A-X systems a r e fully a u t o m a t i c telephone exchanges. Ea,ch uses a: plunger lineswitch-Strowger connecitor s y s tem. In special cases, the Type 50 may also add a selector. The Type 25 Switchboard is adapted for use w h e r e initial requirements a r e near 25 lines and p r o b a b 1e "ultimate" growth will not exceed 75 lines. The Type 50 is used for installations of 35 o r more telephones and where future requirements could approach 100 to 200 lines. More than 1001ines can be a c h i e v e d in the T y p e 50 o n l y by "additional stock' ' equipment. The Types 25 and 50 P-A-X switchboa.rds a r e designed w i t h shelves mounted on sectional frames. The shelves a r e mounted on both sides of end f r a m e s to f o r m a double-sided unit. Shelf units a r e individually located one above the other in a metal cabinet with hinged front and r e a r doors. All switch wiring terminates on terminal blocks located on the shelves. The switchboards can be r e a r r a n g e d easily to facilitate installation of additional equipment in the future. Size differentiates the Type 25 and 50 P-A-X shelves. A Type 50 shelf'section h o l d s 50 lineswitches while the Type 25 is restricted to 25 lineswitches. The Type 50 also has three more connector ~ o s i t i o n s .While the Type 25 can house 7 coniectors, the Type 50 P-A-X can accommodate 10. 'k Figure 10 shows a connector view of a t w o section Type 50 P-A-X Switchboard. The top section accommodates an 11-position connec- tor shelf with eight connectors and associated e q u i p m e n t . The lower section houses the power equipment. Included in the lower section a r e the r i n g i n g apparatus, tone and charge control, and auxiliary service equipment. The lineswitch side of the Type 50 contains t w o sections. The lower portion contains 50 lineswitches and a masterswitch. The upper shelf holds 25 lineswitches with a mechanical link to the masterswitch on the lower section. The upper section also has room for 25 additional lineswitches . In cases where the Type 50 is designed with selectors a s initial equipment, shelves in sect i o n a l cabinets a r e included with the basic equipment. Each shelf mounts ten selectors. The number of selectors used with the unit i s determined by local traffic requirements. The switchboard unit of the Type 25 P-A-X includes one self-aligning plunger lineswitch for each line in service. Each initial "stock" unit of two sections i s equipped with 25 plunger lineswitches, a masterswitch, seven Strowger connectors, a n d associated equipment. T h e connector side contains the power shelf. Here, the voltmeter, ammeter, and ringing apparatus a r e located. The initial unit of 25 plunger lineswitch expands to 50 lineswitches for 50 line capacity. Further expansion is possible with the addition of another unit o f 2 5 l i n e s w i t c h e s . A t o n e a n d charge control relay complete the switchboard equipment. Figure 10. Typie 50 P-A-X Szuitchboard (cornrector side). PLUNGER LINESWITCH CALLED STATION CAYlNG STA ION ?il : a CONN e .a5 = e e e - ee 0 e NORMAL Figure 11. Type 50 P-A-X utilizing Stromger selectors. T h e Type 25 P-A-X r e q u i r e s a 48-volt d-c power c u r r e n t . A battery eliminatoir c a n be used in p 1a c e of the conventional b a t t e r y c h a r g e r system if l o c a 1 commercial power supply is dependable. When a batter:y charger s y s t e m is used, a 23-cell, 48-vollt battery g r o u p and associated c h a r g e r is used. The power s y s t e m used with the Type 50 is essentially that required for the Type 25. Two-digit numbering is required in the Type 25 P-A-X. Usually numbers f r o m 11 to 85 a r e assigned. If lines do not exceed 100, the Type 50 P - A - X a l s o uses a two-digit numbering scheme.