Teletype 33 Operating and installation instructions

TELETYPE CORPORATION
Skokie, Illinois, U.S.A. SECTION 574-123-l00TC
Issue 3, June 1974
33 CALL CONTROL UNIT
GENERAL DESCRIPTION
AND OPERATION
CONTENTS PAGE
1. GENERAL ..... . . . .. . . . . 1
2. DESCRIPTION AND
OPERATION .... . . . . . 1
CALL CONTROL UNIT
FOR SWITCHED NETWORK
SERVICE ........... 1
CALL CONTROL UNIT FOR
PRIVATE WIRE SERVICE .. 8
1. GENERAL
1.01 This section provides a general
description and operation of the 33 call
control units. It is reissued to consolidate 33
information. Marginal arrows are not used to
indicate changes.
1.02 This section describes two call control
units which may be considered basic
units. They are:
(1) Call Control Unit for Switched Net-
work Service
(2) Call Control Unit for Private Wire
Service.
1.03 The call control unit is the electrical
link which joins the various compo-
nents of the set to one another, and the set to the
transmission facilities.
1.04 References to left, right, front, or rear
consider the call control unit as viewed
by the operator.
1.05 This equipment is intendecl. to be oper-
ated in a room environment within the
temperature range of 40° F to 110° F. Serious
damage to it could result if this range is exceeded.
In this connection, particular caution should be
exercised in using acoustical or other enclosures.
2. DESCRIPTION AND OPERATION
CALL CONTROL UNIT FOR SWITCHED NET-
WORK SERVICE
2.01 The call control unit for Switched
Network Service (Figure 1) supplies de
signals to a data set. The data set modulates these
signals into tone frequencies which are trans-
mitted over the telephone lines. A data set at the
receiving station demodulates the tone fre-
quencies back to de signals which are then
handled by the call control unit for operation of
the teletypewriter set. For a better understanding
of the call control unit, 2.02 briefly describes the
data set.
2.02 Start-stop de signal pulses form essen-
tially a square wave which cannot
readily be transmitted over telephone lines. The
data set is basically a converter which changes the
de signals from the sending or calling station into
frequency-shifted tones for transmission over the
telephone network. A marking pulse from a
sending station is converted to a 1270-hertz
marking signal _(Fl mark) and a spacing pulse
becomes a 1070-hertz spacing signal (Fl space).
The data set at the receiving or called station
sends a 2225-hertz marking signal (F2 mark) and
a 2025-hertz spacing signal (F2 space). During
transmission of a message, the calling station
sends a mark and space tones (Fl mark and
space) while the called station sends a continuous
mark tone (F2 mark). In this way the telephone
facilities are operated on a full duplex basis. If the
signal received at either station (Fl mark and
space at the called station and F2 mark at the
calling station) shifts to a space tone for more
than one second, or if the received signal is lost
for one second, the data set will cause the station
to be disconnected. This provides assurance that
the connection is maintained for the entire period
of message transmission.
2.03 The call control unit used with the data
set operates with conventional tele-
phone central offices that have the necessary
© 1962, 1964, 1969, and 1971 by Teletype Corporation
All rights reserved Page 1
Printed in U.S.A.

SECTION 574-123-l0OTC
(Right Front View)
NORMAL-RESTORE
DIALER ___ _
CLR----'
ANS
TST
LCL
SELECTOR MAGNET DRIVER
AND MOTOR DELAY
TIMER CIRCUIT CARD
SPEAKER
Figure 1 -Call Control Unit for Switched Network Service
routing and accounting facilities. In operation, a
call is -originated by depressing the ORlG push-
button (Figure 2). A lamp illuminates the push-
button, and the dial tone will be heard through a
loudspeaker. If the line is busy, a busy signal will
be heard and the clear (CLR) pushbutton (non-
locking) should be depressed. If the line is not
busy, the operator dials the number of desired
station. This causes the called station to go into
connect condition. If the teletypewriter is
manually operated, the called station operator
presses the answer (ANS) pushbutton (non-
locking). Following a short interval, about 1-1/2
seconds, in which telephone facilities are
connected, the called station transmits a mark
tone (F2) and receives a mark tone (Fl) from the
calling station. Receiving the continuous F2 mark
tone from the called station for 1 second causes
the calling station to go into connect condition.
Page 2
and its motor is turned on. Likewise, the contin-
uous Fl mark tone from the calling station for 1
second causes the called station to go into
connect condition, and its motor is turned on.
Either station can now transmit.
2.04 At the end of the message, either
station may originate a disconnect by
depressing the CLR pushbutton, (Figure 2) at
which time each station goes back to its idle
condition, ready to receive or originate other
calls. For keyboard practice, maintenance
purposes, or preparation of copy, the local mode
(LCL) pushbutton (locking) is depressed. This
turns on the motor and disables automatic
answering facilities, if present. In the event of an
incoming call during local operation, the call
control unit responds to ringing signals and the
ANS pushbutton must be operated manually.

ISS 3, SECTION 574-123-l0OTC
ROTARY CARD DIALER .TOUCH-TONE* CARD DIALER
Figure 2 - Call Control Panels
*Registered Service Mark of AT&TCo.
Page 3

SECTION 574-123-lOOTC
Operation of the test (TST) pushbutton (locking)
causes received signals to be retransmitted to the
test center for maintenance purposes. A lamp,
associated with each pushbutton, illuminates the
pushbutton whenever that pushbutton has been
operated and the operating condition exists. The
ANS lamp is pulsed in response to ringing signals
of an incoming call, and lights continuously when
the call is answered. The CLR lamp is automat-
ically extinguished 1.5 seconds after the push-
button has been depressed, and disconnect is
completed.
2.05 A steady mark signal blinds the associ-
ated teletypewriter during all intervals,
except when in the connect condition. This
prevents spurious characters from being printed
except when due to loss of signals, circuit noise,
or deliberate break or space-disconnect signals.
Progress of a Call
2.06 To originate a call, the ORIG push-
button (Figure 2) is momentarily
depressed. This connects the station to the line
and lights the ORIG lamp. During the period of
time in which connection is being made, the
telephone central office makes no time measure-
ments. When the ORIG pushbutton is closed, the
call control unit is connected to the telephone
line through the data set and an off-hook condi-
tion is set up. The amplifier is connected into the
circuit so that the dial tone from the central
office is heard. The called station is dialed while
the amplifier monitors the progress.
2.07 At the called station audible and visible
signaling devices are operated. The
called station goes off hook and into the connect
condition upon operation of the ANS pushbutton
circuit, by manual or automatic means, at the
distant point. At this time, there is a nonsignaling
interval of 1.225 seconds during which
accounting and toll recording facilities at the
telephone exchange will be cleared. Following the
nonsignaling interval, the called station transmits
its F2 mark tone and sets its monitoring timer to
respond to the Fl mark tone from the calling
station. When the continuous F2 mark tone is
received at the calling station for a period of 1
second, indicating that a station has answered, it
will go into the connect condition and turn on its
motor. When the continuous Fl mark tone is
received at the called station for an interval of 1
second, it will go into the connect condition. The
station may now acknowledge the call either by
operator keyboarding, or by automatic answer-
back message transmission. The monitoring timers
Page 4
at both stations are set to respond to reception of
a space tone from the distant station. Traffic can
now be exchanged from either station on a
half-duplex basis.
Disconnecting a Call
2.08 During the time the two stations are
connected (traffic interval), either
station can initiate a disconnect as follows:
(a) A call is normally terminated by the
end-of-transmission (EOT) code
combination which provides fast disconnect
without introducing hit characters. This is
accomplished by the data set in response to
EOT contact closures in function boxes of
both the sending and receiving teletype-
writers.
(b) A call connection can also be cleared
manually by momentarily depressing
the CLR pushbutton (Figure 2). Operation
of the CLR pushbutton at either station will
cause transmission of a spacing signal of
1.5-seconds duration, after which the station
originating the disconnect will discontinue
its tone transmission and go back on hook.
The other station, after receiving the spacing
signal for 1 second, will automatically trans-
mit its 1.5-second spacing signal and then go
on hook. Both stations will then be back in
their original idle condition in which calls
can be either originated or accepted.
Answering a Call
2.09 To answer a call manually, momen-
tarily depress the ANS pushbutton
(Figure 2). This connects the station to the line
and lights the ANS lamp. The lamp remains
lighted until the answer mode is terminated.
Manual answering is necessary only when the
automatic answer-back circuit is disabled. The
automatic answer-back circuit is disabled by
low-paper contacts, data set relay contacts (when
in local mode), and the OUT OF SERV. key.
2.10 Call control units equipped with auto-
matic answering facilities will respond
to received ringing signals, turning the teletype-
writer on at the end of the ringing interval and
proceeding through to the connept condition.
Automatic message answer-back is a part of this
feature. The presence of an operator is required in
order to complete disconnect and return the
teletypewriter to idle condition. For unattended
service, an automatic disconnect timing device

(optional) actuated when a call is answered, will
cause the teletypewriter to go through the
connect condition, send the 1.5-second spacing
tone, and go back on hook if the Fl mark tone is
not received within 8 seconds after the called
station answered. This is designed to prevent the
unattended station from being made busy by
(telephone) calls that fail to cause a full connec-
tion to be set up. This feature does not affect
normal automatic disconnect upon receiving the
1-second spacing tone or loss of tones due to a
dropoff.
Local Mode
2.11 The local mode (LCL) provides off-line
operation of the teletypewriter. The
operator selects the local mode by depressing the
LCL pushbutton (Figure 2). This lights the LCL
lamp and operates the motor control relay (MCR)
to energize the motor. The data set connects the
sending circuit to the receiving circuit and enables
the keyboard and answer-back to transmit. In this
condition the teletypewriter can be used for
preparing copy, for operator practice, or for
maintenance purposes. If an incoming signal is
received during this time, ringing signals are
received and manual operation of the ANS
pushbutton is required in order to receive the
message. If the teletypewriter is in a terminal
hunting group, the operator must tum the out-of-
service (OUT-OF-SERV.) knob to the RESTORE
position momentarily and then to NORMAL.
OUT OF SERV. Switch
2.12 The OUT OF SERV. switch (Figure 2)
prevents the automatic answering of
incoming calls. In its NORMAL position (arrow
on knob upright), it has no effect or function; in
the OUT OF SERV. position (knob rotated
counterclockwise and detented) it sets the
following conditions:
(a) A contact is closed that causes the OUT
OF SERV. lamp to light.
(b) A contact is closed that shorts the
ringer coils. This makes the ringer
inoperative. As an option the contact can be
located to shunt both the ringer and series
capacitor (ie, the telephone line). This makes
the station appear to be in an off-hook
condition or busy to the central office.
(c) A contact is opened that breaks the
automatic answer circuit to the answer
relay. This prevents the relay from operating
ISS 3, SECTION 574-123-l00TC
in response to the ring-up relay and thus the
teletypewriter will not answer.
2.13 For stations that are not in terminal
hunting groups, the operator may
return the teletypewriter to service by turning the
OUT OF SERV. knob to the NORMAL position.
For terminal hunting stations, however, the
operator must tum the knob to the RESTORE
position and hold it until a dial tone is heard. In
this position:
(a) A contact is closed that shorts the tip
to ring (off-hook condition). This
condition is detected by the central office
which then releases the teletypewriter from
lockout and applies the dial tone.
(b) A contact is closed that completes a
path from the speaker amplifier to
ground. This permits the amplifier to pass
the line signals (dial tone).
The OUT OF SERV. switch is then restored to
NORMAL.
Low-Paper Alarm
2.14 A low-paper alarm is provided in the
teletypewriter. When a low-paper
condition occurs, make contacts in the low-paper
switch provide ground to the low-paper buzzer,
permitting it to operate. Depressing the buzzer-
release (BUZ-RLS) pushbutton (locking) in the
call control unit (Figure 2) silences the buzzer
and causes the BUZ-RLS lamp to light. Attempt-
ing to release the pushbutton without replen-
ishing the paper supply will result in the buzzer
operating. When the paper has been replenished,
the teletypewriter is returned to normal by
releasing the BUZ-RLS pushbutton.
2.15 Break contacts on the low-paper switch
disable the automatic answer-back
circuit. The operator can override this condition
by answering manually. If the low-paper alarm
occurs during a call, the operator has the option
of completing the call before changing the paper,
or interrupting the call. To interrupt the call, the
operator stops transmission by depressing the
keyboard BREAK key, and then depressing the
BRK-RLS pushbutton to notify the distant
station of the problem. The connection is cleared
by simultaneously operating the control (CTRL)
and EOT keys on the keyboard. Turning the OUT
OF SERV. knob to the detent position insures
that the teletypewriter will not automatically
answer a call while paper is being replenished.
Page 5

SECTION 574-123-l00TC
2.16 To restore the teletypewriter to service
after the paper has been inserted,
depress the CLR pushbutton and return the OUT
OF SERV. knob (Figure 2) to its NORMAL
position. (For teletypewriters in terminal hunting
groups, tum the knob to its RESTORE position
and hold it there. When dial tone is heard, release
the knob.) The teletypewriter is now in a normal
idle operating position.
Restrain Lamp
2.17 This high intensity restrain (REST)
lamp (Figure 2) lights when a restrain-
ing signal is received from an 8-level to a 5-level
converter used in transmission to 5-level TWX
stations on the DDD switching plan. The lamp
remains lighted until the restraining signal is
removed. The purpose of this feature is to limit
the sending speed from 8-level teletypewriter
transmitting at 100 wpm to 5-level teletype-
writers receiving at 60 wpm.
Test Mode
2.18 If the TST pushbutton (Figure 2) is
operated while the teletypewriter is
connected to a test center, the message sent by
the test center will be recorded on the teletype-
writer and turned around and sent back for
analysis. This is accomplished by connecting the
teletypewriter to the data set through a set of
transfer contacts and a break contact to ground.
This type of operation can be terminated by
momentarily operating any of the nonlocking
pushbuttons which will then release the TST
locking pushbutton.
Signal Generation
2.19 The teletypewriter can send by oper-
ating the keyboard, answer-back
mechanism, or BREAK key (Figure 2). The
keyboard signal generator contacts and answer-
back contacts are in parallel with the signal
generator (distributor) which is, in tum, con-
nected to the data set. The BREAK key connects
to the data set via separate leads.
Dialers
2.20 Pulsing Rotary Dialer: For rotary dialer
applications, a pulsing contact of the
rotary dialer is inserted into the telephone line.
The rotary dialer (Figure 2) is equipped with a
normally closed pulsing contact and a normally
opened off-normal contact. The pulsing contact is
inserted into the telephone line when the station
Page 6
originates a call. When answering the call, a short
circuit is applied across the pulsing contact. The
off-normal contact is placed across the output of
the amplifier and silences the speaker whenever
the dialing disc is moved.
2.21 Pulsing Card Dialer (40A Dialer): The
40A dialer operates on direct current
furnished from the central office. To use the card
dialer, the ORIG pushbutton is depressed. After a
dial tone has been received, a card with the
telephone number punched in it is firmly inserted
in the slot. This operation winds a spring which
later pushes the card out of the slot as dialing
proceeds.
2.22 The card dialer is started by momen-
tarily depressing the START bar. This
operates the card dialer start contact and estab-
lishes a path from the ring side to the tip side of
the telephone line. Sending of the dial pulse
means interruptions of the current in the tele-
phone line.
2.23 A scanning drum makes sixteen revolu-
tions: ten for transmitting the digits
and six for interdigital time. At the completion of
the revolutions, an escapement is tripped which
permits the next row of holes on the card to be
placed in position for sensing.
2.24 This sequence is repeated at each row
as the card advances out of the card
dialer. If no "stop" code is punched in the card,
the card dialer will continue to advance the card
(even if no number code is punched) until the
card is released. If the "stop" code is sensed, the
card dialer stop contacts operate. The card can be
released by operating the RELEASE bar. No
attempt should be made to release the card by
reoperating the START bar, as this will trigger the
card dialer mechanism and place a short circuit
across the output of the data set. This shunt will
prevent the station from receiving or sending until
the card is disengaged. If this condition persists,
the data set will disconnect.
2.25 Pulsing Card Dialer (41A Dialer): In
locations with 60-hertz ac power, the
41A card dialer is used. In this dialer the power to
operate the commutator disc is derived from a
synchronous motor powered by the 14 v ac
source in the teletypewriter. The power to
advance the card in the dialer is derived from a
spring wound by inserting the card in the slot.
The switching functions and the motor control
are independent of the signal path. These features
result in a superior performance as compared with
the 40A dialer.

2.26 To operate the dialer, the card is
inserted and the START bar is momen-
tarily operated. The commutator disc begins
rotating, and the dial pulses are sent to the line.
2.27 When all the punched codes are sent,
the disc stops. A mechanical linkage
then permits the spring, wound by inserting the
card, to advance the card for the next digit to be
read and dialed. As the "stop" code is read, the
dialing stops. The card can then (as also at any
other time) be released by operating the
RELEASE bar.
2.28 TOUCH-TONE Dialer: For multifre-
quency (MF) dialing applications, the
dialing frequencies generated by the TOUCH-
TONE dialer are fed through the loudspeaker
amplifier and into the telephone line via the
sending amplifier in the data set. As the station
connects, the output of the TOUCH-TONE dialer
is disconnected from the data set so that there is
no hazard connected with improper operation of
the TOUCH-TONE dialer at that time.
2.29 The TOUCH-TONE MF signal gener-
ated is a one-transistor oscillator gener-
ating two frequencies any time a single
pushbutton is operated. Seven frequencies are
provided, with each dial digit corresponding to
two frequencies according to the table below:
TOUCH-TONE
Frequencies
cps-1209 1336 1477
+
697 1 2 3
770 4 5 6 Dial
851 7 8 9 Digits
941 10
2.30 The frequencies above 1000 hertz are
generated at a somewhat higher level to
compensate for greater line loss at those frequen-
cies. There is also a variation or amplitude for
various digits.
2.31 TOUCH-TONE and Card Dialer (Figure
2): To use the automatic card dialer,
the ORIG pushbutton is depressed. After the dial
tone has been received, a punched card is inserted
into the slot and pushed down. The START bar is
ISS 3, SECTION 574-123-l0OTC
then momentarily operated. The card dialer
proceeds with dialing under power of a spring
motor wound by insertion of the card. When a
"stop" code is read, the dialing stops. The card
should then be released by reoperating the
START bar.
2.32 The sensing contacts in the card dialer
are in parallel with the frequency-
determining contacts in the associated TOUCH-
TONE dialer. As the card advances out of the
slot, the sensing contacts sense the holes punched
in the card and thus determine the proper
frequencies to be transmitted. This occurs for
every row on the card.
2.33 Since the card advances out of the slot
very rapidly, there is no need for a
separate RELEASE bar. When the station con-
nects, relay contacts in the data set disconnect
the MF signal input and remove any hazard
connected with false operation of the TOUCH-
TONE dialer.
Fuse Protection
2.34 Three fuses protect the components in
the call control unit from accidental
shorts or overloads. They are the selector magnet
driver fuse, the motor delay timer fuse, and the ac
line fuse.
Electrical Interconnections
2.35 A number of nylon plugs and a
terminal strip located at the rear serve
to interconnect the set components to the call
control unit. A six foot power cord connects the
call control unit to the ac power source.
Circuits
2.36 Selector Magnet Driver Circuits: The
data set supplies a 20-mA de signal to
the selector magnet driver associated with the
teletypewriter. The selector magnet driver
amplifies the signal to 500 mA to operate the
selector on the teletypewriter. The selector
magnet driver is a two-stage triggering regener-
ative amplifier (or flip-flop) capable of switching
high output currents of 0.500 ampere at very
closely controlled input current levels. The out-
put of the selector magnet driver is automatically
regulated and is essentially independent of normal
variations in power supply voltage, and of selec-
tor-magnet and current-limiting resistance values.
Page 7

SECTION 574-123-l00TC
RECEPTACLESrt----==
I
(Left Front View)
PLATE
Figure 3 -Typical Call Control Unit for Private Wire Service
2.37 Speaker Amplifier Circuit: The speaker
amplifier is powered only after the
ORIG key is operated and is quieted when the
station connects. It has two inputs, one from the
telephone line via the buffer amplifier in the data
set limiter and the othex-from the multifrequency
(MF) tone dialer. Three outputs are provided: (1)
into the speaker or optional hand-held receiver,
(2) into the telephone line through the sending
amplifier in the data set, and (3) an auxiliary
output into the data set. The line-to-speaker
connection permits monitoring of supervisory
signals when originating a call. The TOUCH-
TONE dial-to-line and TOUCH-TONE dial-to-
speaker connection provides for amplification of
the outgoing MF dialing signals and for moni-
toring them during outpulsing. The line-to-
sccond-output connection is provided for the dial
tone detector (when furnished). The various
connections mentioned are established by
switching in the data set and by the common
switch in the TOUCH-TONE dialer.
Page 8
2.38 Technical Data
Dimensions (Approximate)
Width
Length
Height
. 5 inches
.17 inches
. 6 inches
Input . . . . . . . . 115 v ae±10%, 60 Hz
Environmental conditions . . . . 40° F to
110° F ambient temperature
CALL CONTROL UNIT FOR PRIVATE WIRE
SERVICE.(Figure 3)
2.39 Power for the motor, selector magnet
driver, local power supply, and tape
reader power pack, is supplied from fused 115
volt ac, 50 to 60 hertz power. Direct current of
either 0.020 or 0.060 ampere is required for the
signal line(s) and for operation in the local mode.
The de power for the signal line(s) is supplied by

external facilities, while local de current for
operation in the local mode is furnished through
the operation of the local power supply circuit in
the call control unit. At the rear of the call
control unit is a terminal strip which provides the
point of entry for the ac power and signal line(s)
into the teletypewriter set.
Note: Normally the tape reader power
pack comes from the factory installed in the
call control unit; optionally the power pack
may be mounted in the stand. See Section
574-100-201TC.
2.40 A 3-position rotary power switch is the
only manual control on the call control
unit. Its three positions are: OFF, LOCAL, and
LINE.
Fuse Protection
2.41 Two fuses protect the components in
the call control unit from accidental
shorts and overloads. They are the selector
magnet driver fuse and the ac power line fuse.
Electrical Interconnections
2.42 Connector plugs at the rear of the call
control unit serve to interconnect the
set components to the call control unit. A
terminal strip, also located at the rear, serves to
connect the ac power to the call control unit and
offers a convenient terminating area for other
accessories and external connections.
Line Mode
2.43 When the switch is in the LINE posi-
tion, the teletypewriter is placed in the
external signal line loop for communication with
other teletypewriters. The external signal line
ISS 3, SECTION 574-123-l0OTC
loop is united with the selector magnet driver.
With de power on the signal lines, transmission
from the keyboard or tape reader will cause the
typing distributor to send start-stop signals to
other teletypewriters in the external signal loop.
Also, the local teletypewriter is able to receive,
through the typing unit selector, the start-stop
signals transmitted from other teletypewriters in
the signal line loop.
Local Mode
2.44 When the switch is in the LOCAL
position, (1) the local battery is
supplied to the selector magnet driver and the
send circuit, (2) the external signal line loop is
divorced from the selector magnet driver, and (3)
the external signal line loop is shunted so that
other teletypewriters in that loop can communi-
cate without being affected by the operation of
the local teletypewriter.
Off Mode
2.45 When the switch is in the OFF position,
the signal line is diverted around the
local teletypewriter. Other teletypewriters can
communicate in the signal loop without interfer-
ence. All power in the call control unit, except
the ac power to the selector magnet driver, is off.
2.46 Technical Data
Dimensions (Approximate)
Length .
Width .
Height .
. .15 inches
4-1/2 inches
. . 6 inches
Input . . . . . . . . . 115 v ac, 50-60 Hz
Environmental conditions . . . . 400 F to
110° F ambient temperature
Page 9
9 Pages