|The Post Office introduced the Answering
Machine No. 2 in 1963. Like its predecessor (Answering Machine No. 1
) it was an answer only model,
but with a longer message facility (of up to three minutes), this second
version was more suited for use on information lines. Its first use was
in Birmingham, for a "Dial-a-Prayer" service.
C MARKETING - INSTALLATION
ANSWERING SET No. 2A
Instruction describes the Answering Set No. 2A, which provides automatic answering and a
subscriber's information service in the form of a pre-recorded message. The Answering Set
No. 2A is a development of the Answering Set No. 1 described in M1000 and many features are
common to both machines. This Instruction gives a detailed description of the features
peculiar to the Answering Set No. 2A.
Appearance and size
Features common to Answering Sets Nos. 1 and 2A
Ringing delay and tape control
Replacing the tape
Operating the machine
Precautions during installation
Answering Set No 2
The Answering Set No. 2A is powered by an ac mains supply of 110V or 200-250V at 50 hz. It
is designed to answer an incoming call automatically and play a pre-recorded message of
any duration between 30 seconds and 3 minutes. The message is transmitted once before the
machine releases the line. To make a recording the message is recited into the transmitter
of the associated telephone or a telephone specially provided for the purpose. The volume
is monitored by the sidetone facility) incorporated in the telephone. The recording may be
checked by playing back into the telephone used for making the recording.
Provision has been made for a number of machines, each terminating an incoming-only line,
to be installed at a subscriber's premises. Under these conditions a recording can be made
on one machine and transferred to all other machines, in turn, by a patching cord.
A single machine is suitable for use on exclusive DELs, two-wire PMBX extensions and PABX
extensions not arranged for direct night service, in automatic areas. It cannot be
connected to extension plans or house exchange systems because the purpose for which the
machine is provided is not appropriate to such installations.
Appearance and size
In colour and size the Answering Set No. 2A is identical to the Answering Set No. 1.
Differences in appearance are the repositioning of the start button and pilot lamp, and
the absence of a recording time indicator; the subscriber must time his own recordings
according to the length of tape loop he has requested. The case and front plate are not
interchangeable those of the Answering Set No. 1. The machine is supplied with an eight way
36 in cord terminated on a Connector No 202A11A, and 12 ft of mains cord.
Features common to Answering Sets Nos. 1 and 2A
The following items are common to both machines.
(a) Record replay amplifier
(b) Power supplies
(c) Motor, flywheel, idler and pinch wheels
(d) Erase and record/replay, heads
(e) Control knob and key.
(a) Chassis assembly
The chassis consists of a sloping plate with two strip steel supports. Mounted. on the
sloping plate are the tape transport mechanism, relays, tape storage cassette and multiple
wafer switch. Relays A, AA and B are Type 16 relays mounted on a bracket recessed into a
rectangular hole in the chassis. It is only necessary to release the two screws securing
this bracket and draw the whole assembly forward, to gain access to the relays for
inspection and maintenance. The tape transport mechanism includes a redesigned pressure
pad arm. The pressure pads are mounted on a cross member which rocks on the end of the
tensioning arm to maintain constant Pressure on both heads. The storage cassette is
secured to the chassis by three long screws through the cassette supports.
(b) Tape storage
The tape is stored as free convulations in a die cast aluminium tray which has a
smoothed, clean, finish. The ends of the cassette are curved to assist the movement of
convolutions around the cassette. A clear plastic cover is secured by five fixing screws
to the top of the cassette. An encapsulated assembly containing a small socket, a
photocell and a lamp for tape cycling control is secured by two screws underneath the
cassette. A slot is provided in the cassette wall, at the lower left-hand corner, for tape
(c) Tensioning adjustments
Screw adjustments are provided for the springs tensioning the pinch wheel arm, the idler
wheel and the pressure pads. Details of the tensioning are given in the maintenance
instruction, G 5010, for the Answering Set No. 1.
(d) Ringing delay and tape control circuits
The thermal relay and tape bump operated microswitches, which provide ringing delay and
tape control in the Answering Set No. 1, are replaced by electronic circuits in the
Answering Set No. 2A. These circuits are located on a printed circuit board mounted
vertically on the left-hand side of the chassis. An adjustable potentiometer is provided
at the top corner of the board for adjusting the period of ringing delay. Adjustments are
not provided in the tape control circuit which relies on transistor circuitry for its
The tape is double coated and graphited instrument tape formed into a continuous loop with
a 180 degree twist in its length. This is known as a continuous loop. A small hole is punched
near one edge of the tape, close to the joint, which allows light from the tape control
lamp to impinge on the photocell, thus stopping the tape drive and releasing the line at
the end of the message.
The Mobius loop principle is utilised to enable a maximum three minute message to be
recorded on a 1 and a half minute tape loop. When the start button is pressed at the
commencement of a recording, the entire tape loop is driven past the heads, and a
half-track recording is made on one side of the tape. At the end of the tape cycle, the
hole passes the light beam but is near the lower edge of the tape and passes below the
beam. Hence, no control signal is generated. The tape section with the hole then passes
through the twist compartment and is turned over, allowing further recording on the other
side of the tape and a different track. The entire tape loop passes over the heads for the
second time. When the hole passes the light beam at the end of the second traverse, it is
near the top edge of the tape and allows light to reach the photocell thus generating the
control signal to stop the tape and release the line.
Replacing the tape
If it is necessary to change the tape the following procedure should be adopted:-
(a) Turn the switch to OFF and remove the knob using the hexagonal wrench located in the
(b) Release the four cover screws and remove the cover.
(c) Remove the transparent cassette cover, noting how the tape twist is located in the
twist compartment. The twist, when viewed along its length towards the heads, should be in
the clockwise direction. Remove the tape from the cassette.
(d) Locate the twist in the new tape. A recommended method is as follows. Open the tape
loop to its full extent and place the middle finger through the loop at one end allowing
the tape to hang freely. Close the fingers to trap the tape each side of the middle
finger. Draw the tape through the fingers until the far end of the tape is approached when
the twist will be apparent.
(e) Hold the tape at each end of the twist, allowing about 3 inches between the points
held and insert the tape into the two slots at top and bottom of the twist compartment.
(f) Thread the lower end of the tape between the lamp and photocell and the top end
through the tape transport mechanism. Finally, bring both ends out of the cassette via the
slot in the cassette wall.
(g) Replace the cassette cover, turn the switch to CHECK and press the START button. The
tape will be gradually drawn into the cassette and form its own free convolutions. Care
must be exercised to ensure that the tape outside the cassette does not become entangled
or collect dust from the floor. If the tape becomes entangled, switch the machine off and
carefully unravel the tangles before restarting the machine.
(h) When all the tape is inside the cassette allow the drive to continue until stopped by
the operation of the control circuit.
(j) Replace the case, cover plate, knob and hexagonal wrench.
The complete circuit is shown on Dgms N603 and SA 5136 and operates as follows:-
(a) Answering a call
When the machine is switched on, but quiescent, the transistor TR3 is switched off. This
transistor with TR4 acts as a trigger circuit. The Zener diode D5 is not conducting so
that there is no base bias to switch TR3 on. Hence TR4 is switched on but the negative
potential at the collector is insufficient to switch on TRS and operate relay B.
When incoming ringing current is detected, relay AA operates and contact AA1 operates
relay A which locks via its own contact A1. Contact A2 removes the 8V supply maintained by
Zener diode D1 while contact A3 extends the a.c. supply to operate the call meter, if
fitted. The standing charge on capacitor C2 leaks away via RV1 and after a nominal period
of 10 seconds TR1 and TR2 cease to conduct. The potential at TR2 collector reaches
approximately -5V and Zener diode D5 conducts extending this potential to the base of TR3,
switching this transistor on. Transistor TR4 switches off and extends a high negative
potential to the base of TR8 causing it to switch on, thus operating relay B. Contacts B3
and B4 connect the line transformer to line which trips the incoming ring. Contact B2
releases relay A and contact B1 operates relay C. Contact C1 starts the motor and the
message is transmitted to line. Although contact A2 has restored, relay B is held because
TR7 is now switched off and a high negative potential is applied to the base of TR8 to
maintain its switched on state. Diodes D7 and D8 form an OR gate, and TR7 and TR8 form a
(b) Cessation of the message
When the hole in the tape loop passes through the photocell gate for the second time, the
photocell is actuated by the light beam passing through the hole in the tape. This causes
current to flow in the photocell circuit and TR5 is switched on. A 15k ohm temperature
sensitive resistor in the photocell circuit compensates for changes in the photocell
characteristics due to temperature changes. Transistor TR6 switches off and the resulting
increase in negative potential on the collector forward biases diode D6 to switch TR7 on
again, thus switching off TR8 and releasing relay B. Contacts B3 and B4 release the line,
and BI and B2 switch off the motor and reconnect relay A ready for the next call.
When it is desired to make a recording, the switch is turned to RECORD and the START
button pressed and released. This connects the dc supply to relay B, thus starting the
motor and ensuring that TR7 is switched off and TR8 on. At tile end of the recording the
photocell operates as in (b).
During the recording, the erase head is energised and erases any previous message. A dc
supply of about 45 ma is extended to the telephone from the machine to feed the
After recording, the message should be checked by turning the switch to CHECK and again
pressing and releasing the START button. The control circuit operation is the same as in
(c) but the erase head is not energised.
Operating the machine
A copy of How to use the Answering Set No. 2A (form A 1377) should be given to the
subscriber and he should be given a demonstration to ensure that he understands the
A summary of the operating instructions is given below.
(a) Single machine on a bothway line.-
(i) To make a recording - Allow at least 30
seconds after switching on for the machine to warm up. Turn the switch to RECORD and lift
the handset. Press button firmly and release. When the motor the START indicator begins to
rotate speak into the telephone transmitter in the normal manner. The duration of the
message should fill the whole of the tape capacity.
(ii) To check the recording
Turn the switch to CHECK and proceed as in (i). The message is played back via the
telephone receiver. If the recording is unsatisfactory in any way, a fresh recording
should be made. The first recording is automatically erased at the time of re-recording.
(iii) To answer an incoming call while a recording is being made or checked
When the switch is turned to RECORD or CHECK an incoming call will ring the telephone
bell. To answer the call turn the switch to OFF and lift the handset. If the call
interrupted the record or check procedure it is necessary to run the tape back to the
start position by operating the START button before re-recording or checking. The new
recording must be started from the beginning.
(iv) To connect the answering set to line
When the recording has been checked and judged satisfactory it is only necessary to turn
the switch to ON for the machine to answer calls.
(b) Multi-machine installation on incoming only lines
(i) To make a recording
Select a free machine and turn the switch to RECORD. Insert the telephone plug into the
jack associated with the machine and press the START button firmly and release. Proceed as
in (a) (i) The line is busied during recording and no incoming call will interrupt the
(ii) To check the recording
Turn the switch to CHECK and insert the telephone plug into the associated jack. Proceed
as in (a) (ii) the line is again busied while the recording is being checked.
(iii) To transfer the recording to other machines
A patching cord with a plug at each end is provided to enable the recording on one machine
to be transferred to 11 other machines in turn. Insert the plug on one end of the
patching cord into the jack associated with the machine from which the recording is to be
transferred. Turn the switch on this machine to ON. Ensure that the machine to which the
recording is to be transferred is free and insert the plug on the other end of the cord
into the jack associated with this machine. Turn the switch on this machine to RECORD.
Press and release the START buttons on both machines simultaneously. The lines to both
machines are busied during the transfer.
(iv) To check the transferred recording
Remove the patching cord plug from the jack associated with the machine bearing the
transferred recording and insert the telephone plug. Turn the switch to CHECK and the
recording can be checked via the telephone handset as in (a) (ii). The plug on the other
end of the patching cord should remain in the jack to prevent the machine bearing the
original recording being engaged by a caller.
(v) To connect the machine to line
The procedure is the same as (a) (iv). If a machine becomes faulty it is only necessary to
turn the switch to OFF to busy the line and immobilise the machine.
The Answering Set No 2A can be installed in either of two ways. It can be installed as a
single machine with telephone connected to a bothway line or it can be connected as a
multi-machine installation without telephone, each machine connected to an incoming only
line. For a multi-machine installation a Telephone 706CB is provided for checking and
making recordings. Dgm. N 4191 details these two types of installations, which are
described as follows:-
(a) Mains power supply
This is described in M1000 but the P.O. must provide the appropriate mains plug.
(b) Connecting the machine for a single machine bothway line installation
(i) Remove the base and check the mains voltage setting. The voltage adjustment is
located under the removable panel marked DANGER.
(ii) Fit the appropriate three-pin mains plug, connected as shown on Dgm. N 603.
(iii) Rearrange the telephone and answering set straps according to Dgm. N 4191. The
answering set is supplied with a line cord terminated by a plug coded Connector No
202A11A. A jack, coded Connector No 202D11B, is required to mate with the plug. The jack
should be mounted in a mounting plate Part 8/DMO/32, and case Part I/DCA/94. The telephone
cord should be changed to Cord Instrument, No 5/37AA, Grey, and the terminal block
replaced by Block, Terminal, No 36A, Grey. Eight-wire cable should be used between the
terminal block and Connector No. 202D11B. The line should be connected to this terminal
block. If required by the subscriber, a Meter No. 19, Grey can be connected to the
terminal block for call counting.
(c) Connecting the machine for a multi-machine incoming only line installation.
(i) Proceed as in (b) (i) and (ii).
(ii) One Telephone 706CB, Grey should be provided for recording and checking messages.
Recover the telephone line cord and terminal block and fit a Plug No 505 with Cord,
Instrument, No 5139AD, Grey modified in accordance with Dgm N4191. The telephone straps
and cord terminations are also shown on this diagram. The connectors and parts detailed in
(b)(iii) should be fitted, one each per machine. The answering set straps must be changed
as indicated on Dgm N4191 a jack No 96A should be fitted for each line connection and
six-wire cable should be used to connect the jacks to Connectors No 202D11B. The Meter No
19, Grey is an optional feature for each machine and is connected to the Connector No
202D11B. A patching cord for transferring recordings is required and this must be
constructed from a Plug No 505 with Cord, Instrument, No 5/39 AD, Grey terminated by
another Plug No. 505 in accordance with Dgm N4191.
Precautions during installation
These are detailed in M 1000 but the reference to the recording time indicator does not
apply. Extra care must be taken to observe the warning concerning installation in the
vicinity of strong ac fields and it must be ensured that the wiring and cords of the
answering set are not adjacent to machines such as teleprinters.
Answering Set No. 2
This machine, of which only a small number were manufactured, was the predecessor of the
Answering Set No. 2A. Installation details are the same as for the Answering Set No. 2A and
circuit details are shown on Dgms N603 and SA 5136.