|See also Telephone No. 735 - Red renters POA
See also additional information on BCC No. 705 - armoured
BCC No. 700 was introduced circa 1959 in the Bristol STD area. The box
accepted 3d bits, 6d and one Shilling coins.
Issue 1, April 1971
CALL-OFFICES AND SUBSCRIBERS COIN-BOX INSTALLATIONS
Mechanical and electrical operation of Box, Coin Collecting No. 700 & 705 (POA type)
The Box, Coin-collecting, No. 700 (shown to the right) is used in
conjunction with a 700-type telephone on subscribers' installations. The circuit is shown
in Dgm. N 1169 and the coin-collecting box associated with a Telephone No. 706 in Dgm. N
2423. The Box, Coin-collecting, No. 705 (shown below) is a combined telephone and coin
box, the integral telephone being of the 700 type. The circuit is shown in Dgm. N 805.
The coin mechanism is a Mechanism No. 20.
Those coin boxes have been designed to enable users to obtain trunk calls, in
addition to local calls, without operator assistance. They are for connection to public
exchanges which provide subscriber trunk dialling facilities. In use the wanted
subscriber's number is dialled, and it is not until after the called party has answered
that coins are inserted. For this reason the system has been designated 'Pay-on-Answer'.
The coin boxes accept 12-sided threepenny pieces, sixpences and shillings and signal
the value of the coin(s) inserted to the exchange. The coins, if accepted after passing
the coin tests, drop straight through to the cash container and are not held in suspense. There are therefore no 'A' or 'B' buttons but a reject chute is provided to return worn or
The circuit for the bell is completed via the gravity switch as long as the hand- set is
on its cradle, and the instrument functions as a normal telephone for incoming calls. The
coin slots remain locked throughout an incoming call.
Outgoing calls - sequence of events
The caller lifts the receiver and dials the wanted number. Until the called subscriber
answers the line polarity is such (A-line positive) that relay SU does not operate and the
coin slots are locked to prevent premature insertion of coins. When the called subscriber
answers the line polarity reverses, and relay SU operates unlocking the coin slots. At
this stage there is no speech path but the caller receives pay cone (N.U. tone interrupted
at 0.125 second on, 0.125 second off) and should then insert a coin. The insertion of a
coin causes coin pulses to be sent to the exchange where they are recorded by the coin and
fee checking relay-set, which then opens the speech path, so that conversation can
proceed. Further coins can be inserted at any time and corresponding coin pulses are sent
to the exchange as above. At each termination of paid for time, pay tone is re-applied to
line for three seconds (the speech path is still open during this pay tone). If a com is
not inserted within 10 seconds of the commencement of pay tone, a line reversal re-locks
the coin slots and two seconds later the call is force released at the exchange and N.U.
tone returned to the caller.
Coin value signalling
The coin pulses are signalled by increasing the line loop resistance by 5000 ohms. The
coin pulses are sent at approximately 4 pulse/sec. with a signalling resistance/loop
resistance timing ratio of 1:1.6. Each coin pulse train terminates with a line
disconnection of 60 ms and if this final disconnection is absent the pulse train is not
accepted by the exchange equipment, i.e. the call is regarded as a fraudulent operation.
The energy for generating the coin signals is obtained by the insertion of' the coin. When
the coin is pressed into its slot it operates a pivoted lever, the movement of which
raises a bank of cams. When the coin is fully inserted the cam-bank falls under gravity
but at a speed regulated by a dial-type governor. As the cams fall various spring-sets are
operated to produce the coin pulses, but the pulses are not sent to line unless the coin
has successfully passed through the coin tester and tripped the mask operating lever. The
number of pulses sent depends upon the coin used, a 3d., 6d. or 1s. coin sending one, two
or four pulses respectively. Generation of the correct number of coin pulses for the
particular coin inserted is effected by moving a pivoted coin-pulse spring-set to be
opposite the appropriate cam on the cam-bank. With reference to Dgms. N 805 and N 2423,
the spring-sets produce coin pulses as follows:-
(a) CPON3 makes and prepares a circuit for CP.
(b) The mask contact opens, leaving the telephone loop held via CP and CPON3.
(c) CPON1 makes, and short-circuits the receiver.
(d) CP opens and introduces 5000 ohms into the loop, this being the first coin pulse.
(f) CPON2 makes and prevents operation of the gravity switch interfering with coin
(g) CP closes and completes the first coin pulse. If the coin inserted is 3d., CP
operates once only, if 6d. CP operates twice and if 1s. CP operates four times.
(h) CPON3 opens and gives a line disconnection ('coin train complete' signal).
(j) The mask contact closes and re-establishes the loop.
(k) CPON2 opens, CPON1 opens and the circuit is restored to normal.
Coin slot locking
The slot locking is controlled (a) electromagnetically by the exchange equipment, relay SU
being used for this, and (b) mechanically within the coin-operated mechanism itself. The
coin slots are normally locked but are unlocked when the distant subscriber answers and,
in general remain unlocked for the duration of the call. The full sequence is:-
- The slots are locked when there is no line current (handset on its cradle, circuit
faulty, etc.) or when the line polarity is normal.
- Relay SU unlocks the slots when the called subscriber answers and the line
- The slots are relocked, momentarily, during the signalling of a coin (a period of
approximately two seconds) to prevent the premature insertion of a second coin. They are
also interlocked to prevent the simultaneous insertion of two or more coins, or the
last-moment substitution of one coin by another (for example by withdrawing a Is. and
inserting a 3d. coin, in a fraudulent attempt to obtain ls. worth of time for 3d.).
- Finally, relay SU relocks the slots two seconds before forced release at the end
of pay tone to prevent coins being inserted too late during the 12-second pay period to be
recorded at the exchange.
(a) 'Emergency service' facility
If the Mechanism No. 20 is removed and taken away, e.g. to a coin-box maintenance centre, the
telephone circuit can be retained for emergency service by coupling a 4-point jack to a
4-point plug (connector SJ, see Note 3 Dgms. N 805 and N 2423). A label that the telephone
is available for emergency calls only is then fitted over the coin plate aperture. The
4-point jack (jack No. 77D) and the label (label No. 360) used for this purpose are housed
in the mechanism compartment of each coin box.
(b) CPON3 contact
This contact is made as soon as the Cam-bank starts to move downwards after a coin has
been inserted. It must make before the mask contact opens. If it fails to do so, the
telephone line is open-circuited and the call is released. A failure here may occur due to
incorrect adjustment of the CPON3 spring-set assembly so that it fails to latch, or
incorrect positioning relative to the cam-bank so that the operating mechanism is not
prepared on the upward movement of the cam-bank.
(c) The telephone regulator
This is part of the 700 type telephone and is used to reduce the sensitivity of the
telephone on short lines. If a regulator fails, and a spare is not to hand, the telephone
circuit can be temporarily restored (but without regulation) by withdrawing and reversing
the regulator end-for-end in its jack. In the reversed position the contacts on the
regulator bridge jack points B, D and C.
(d) Rectifier MR2
This is a selenium double-diode having the purpose of minimising the clicks in the
receiver during the progress of a call, especially those arising from the line current
reversals used to control slot locking.
(e) SU relay
This is a 3000-type relay used to perform mechanical work only; bias spring-sets are
provided to control the armature, but the springs have no electrical contacts. The relay
is 'polarised' by the use of a rectifier, so that with the initial conditions (A-line
positive), the series element does not conduct and therefore relay SU does not operate.
When the line polarity is reversed, e.g. called subscriber answer the series element does
conduct and relay SU operates. The shunt element is provided to maintain the line current
when the series element is not conducting.
(f ) The mechanism test jack
An 8-way jack, T.J., is provided, at which access to the isolated contacts of the pulser
unit can be obtained for maintenance purposes. The strappings required for normal working
are provided by a plug which is normally inserted in the jack. The jack enables faulting
to be carried out and is used for the setting up of the mechanism in coin-box maintenance
centres, in conjunction with a Tester SA 9129.
(g) Earthing of coin-box casing
The earth connected to the appropriate coin-box terminal is extended to the mechanism
framework and the metal casing or cover. This is done to ensure that if low insulation
conditions arise, shocks will not be experienced by users. In addition, contacts to the
frame or casing will show up as definite earth faults instead of giving rise to low
insulation or noise faults which may be difficult to trace.
Taken from EI Telephones, Call Offices D1010
Picture below shows BCC 700 type as it would be supplied
to a customers premises