3 Internal
Issue 1, Aug 1983

(BT Payphone 100)



The Coin Telephone No. 23B (CT23B) is a self contained, micro-processor controlled telephone capable of working in a DEL mode or as a Payphone with restricted facilities. It is. a renter's telephone designed for use in supervised locations such as Public Houses, Business Reception desks and families with large telephone bills i.e. with teenage children.

The mode of the CT23B is controlled by a lockable switch. When the "O" symbol has been selected the CT23B works as a normal DEL with access to IDD, STD and all operator services. Calls will meter on the associated exchange meter and the customer charged in the normal manner.

Selecting the "P" symbol converts it into a payphone with restricted facilities. In this mode it will accept 2p, 5p, 10p and 50p coins but there is no access to operator services (or any lxx codes) except for '999' calls.

The CT23B cannot be used in plan numbers (except Phonesocket where an extension can be added) or on shared service lines.

The instrument has been styled to harmonise with the New Generation Telephones incorporating a keypad and a new styled handset. Due to the styling the payphone does not have a high degree of security and therefore the installation should be in a well supervised location. It will be possible to screw the CT23B down to a shelf or to chain it by a clasp fixing at the rear of the cash compartment.

The line cord is a Cord Connecting No. 4/500 3000 mm which is plug ended at the Line jack 2/7A and at the telephone.

The handset cord terminates on a plug and socket inside the payphone to allow for ease of replacement.

Above the keypad there is a Credit Display window which consists of a Red Light Emitting Diode (LED) which flashes advising the customer to insert money. The minimum call charge fee is also displayed in this window.

The CT23B is provided with a Tone Generator calling device similar to the Trimphone.

The dimensions are 180 mm (height) x 230 mm (width) x, 200 mm (depth) and it weighs 3 Kgs (empty).

At the CCB Installation or Payphone Maintenance Centre (PMC) each CT23B should be carefully unpacked and a check made for any discrepancy and/or damage. It is advisable prior to installation to ensure that the CT23B operates successfully. The connection of an ORD exchange line with SPM facilities and a signalling earth to the CT23B will enable the coin telephone to be tested in accordance with this instruction. To enable the payphone to be tested the battery will need to be installed.

The CT23B should be installed in accordance with Diagram N 2825.

The following item should be requisitioned.. -

Coin Telephone No. 23B ... colour Battery Secondary No. 34 Line jack Unit 2/7A Block Terminal 80A

NOTE: The lockable mode switch and cash box lock are already fitted on delivery of the CT23B.

Mode Switch and Cash Box Key Procedure
The keys for the mode switch and cash box are sealed in an opaque heat sealed envelope and will have been removed from the CT23B packing case on arrival at the local stores. The keys would then have been sent to the Call Office duty in the appropriate Sales Group, along with parts 2 and 3 of the serial number card, by the Storekeeper. The Call Office duty would then send the keys direct to the customer on receipt of the Advice Note (AN). The Fitter will receive part 2 of the card associated with the buff copy of the AN, this will enable the correct CT23B to be issued to the Fitter by the Storekeeper. Part 3 of the card should be completed and forwarded to the Sales Division by the Distribution Officer in the Installation Office.

Cash Compartment/Mode Switch Key Handling
The following procedure is suggested to ensure a secure method of handling the associated keys.

The exterior of each CT23B carton will be stamped with a serial number. Enclosed within the carton will be a heat-scaled opaque envelope containing two keys for the cash container and two keys for the mode switch. Associated with this envelope will be a three part card.

  • One portion to remain with CT23B.
  • The second portion to be associated with TELE No Buff copy of AN.
  • The third portion to be forwarded to TELE No Sales for completion of A4488.

The carton should be opened by the Storekeeper or the Maintenance Repair Centre staff, dependant on Area organisation, and the envelope containing the keys be removed. Parts 2 and 3 of the serial number card should then be sent, with the keys, to the Sales Renters Payphone Duty. Part 1 of the card should be kept in the carton for reference purposes only.

The Sales Coinbox Duty should store the keys until required. When an AN for a CT23B is issued a serial number should be allocated from the keys in store and noted on the AN. The AN plus parts 2 and 3 of the card should be forwarded to the Installation Control. The card A4488 should be completed in the normal manner and the keys forwarded to the customer by recorded delivery.

On receipt of an AN at the Installation Control, the Installation officer should complete parts 2 and 3 of the card. Part 2 should be attached to the AN and given to the Fitter. Part 3 of the card should be forwarded to the Sales Division.

The Fitter should present the AN with part 2 of the card to the Storekeeper. The Storekeeper should identify the correct carton using the serial number and issue the CT23B.

Fitting Instructions
The CT23B must be connected to an exchange line with Subscriber Private Metering (SPM) facilities.

A signalling earth must be provided at the customers premises. Wire Earthing, 9141 /1W should be used to connect the signalling earth to the Line jack Unit of the CT2 3B, via a Block Terminal 80A.


The CT23B is line powered with a battery to maintain the memory and supply a regulated power output. The battery is a Battery Secondary No. 34 and should be installed fully charged.

To install the battery: -

(i) remove the moulded case. To achieve this loosen the two retaining screws at the rear of the case using a Ringdriver No. 9.

When removing the case, gently lift rear of the case whilst easing it forwards.

After the case has been removed the battery compartment can be seen at the top left-hand corner of the mechanism compartment.

(ii) unclip and lift the processor board. To secure the board in the raised position slide it either to the right or left.

(iii) remove the mode switch, this enables the battery to be easily installed. To remove the mode switch unclip the right-hand side of the mode switch bracket. Slide the bracket towards the rear of the case. Lift the switch and bracket out and lay to the side of the telephone.

(iv) clip the Battery No. 34 onto the support bracket, see Fig 5.

(v) replace the mode switch using the reverse procedure as described in (iii).

(vi) release and lower the processor board.

(vii) the battery leads are connected to the battery socket which is situated under the key- pad board (Marked PL2/batt). To remove the keypad board just lift up, this will expose the notch which accommodates the battery leads. Replace the keypad board.

Cash Compartment Lock
The cash compartment lock is a Lock No. 2/41A. The lock has already been fitted by the manufacturer.

Mode Switch Lock (Lock No. 58A)
The mode switch lock has been fitted by the manufacturer.

Telephone Number/Minimum Fee Label
The telephone number label should be positioned under the clear plastic label holder. To remove this plastic holder gently ease it out by pressing down at either end and prising it off. Insert the label and replace the plastic holder. The minimum fee label window is removed by pressing down on the right-hand side and gently easing off. These labels can be requisitioned from SND/P1.1.

Minimum Fee Label: - LAB 542A Telephone Number Label: - LAB 542B

Fixing CT23B to a Shelf
If fixing to a shelf is requested by the customer this may be achieved by carrying out the following: -

(a) ask the customer to unlock and empty the Cash Compartment,

(b) remove the case,

(c) remove the mechanism compartment from the cash compartment. Unclip torsion bar, lift off the entire mechanism and put it in a safe place. The cash compartment is now left on its own,

(d) screw the cash compartment to the appropriate shelf using two screws placed in the top right-hand and bottom left-hand corners (viewed with the cash box lock to the front). To enable the top right-hand screw to be fitted, the torsion bar supporting collet will have to be removed. Once the screw has been installed replace the plastic collet.


(e) replace the mechanism and re-clip the torsion bar,

(f) relock the cash compartment,

(g) replace the case cover.

Fitting a Clasp (Part No. I/DLC/184) to the Rear of the CT23B This can be achieved in a similar manner as described above but instead of screwing to a shelf a clasp is bolted to the rear of the cash compartment using the two knock out holes situated on the rear panel.

The minimum fee (mf), unit free (uf) and M rate (internal timer if the SPM rate is greater than the M rate that has been selected) are stored in the CT23B by using the keypad and the associated tariff button (located on the speech board within the mechanism compartment).

If at any time during the call the received SPM period exceeds a value "M" the payphone applies a tariff, equivalent to a SPM period, "M" charging reverts to being based on the received SPM Pulse period only if it becomes less than the value "M".


Method the following method should be carried out with the case removed and the processor board in the raised position (to gain access to the Tariff Button).

NOTE: Because the case has been removed release the gravity switch and check for dial tone.

Press and release the tariff button situated on the speech board, see Fig 6. Dial tone is replaced by tones to state that the tariff has not yet been set. The tones are: -

1 second of 800 Hz

1 second of 400 Hz repeated 3 times. Pause followed by a continuous tone lasting for 3-8 seconds. At the end of the continuous tone the CT23B is ready for the tariff to be set by using the keypad. The tariff is in the form of 5 digits as follows: - Digit: 1 2 3 4 5 m Rate Minimum Fee (in pence) Unit Fee (in pence)

NOTE: If minimum fee or unit fee is less than 10 ensure that two digits are set i.e. 08 or 09. M Rate is represented by pips of tone (400 ms of 400 Hz followed by 600 ms of pause). M = 1 pip (90 secs) = 2 pip (120 secs) = 3 pip (180 secs) = 4 pip (Infinity i.e. no internal timer)

Therefore to insert a tariff setting of minimum fee 8p, unit fee 6p and no internal timing the five appropriate digits are keyed i.e. 08064.

When valid tariff has been received the new data (in the form of tones) are played back. Then dial tone will be heard and the red LED (minimum fee) will glow.

Check of Tariff
A check can be made to ensure that the correct tariff has been stored. This is carried out by pressing the tariff button. A set of tones will be heard describing the tariff information.

The information is as follows: -

5p Fee value............... 300 ms of 800 Hz followed by 200 ms pause
lp Fee value............... 400 ms of 400 Hz followed by 600 ms pause so that 6p will be represented by 800 Hz.400 Hz

Example: - For tariff digits 08064 tones heard: - 800 Hz.400 Hz.400 Hz.400 Hz . . . 800 Hz.400 Hz . . . 400 Hz.400 Hz.400 Hz.400 Hz Followed by a continuous tone lasting 3-8 seconds.
NOTE: the first tone of each set is always the 5p tone (800 Hz), if applicable. After checking if the tariff information is correct wait approximately 30 seconds and dial tone will be restored. If the tariff information is incorrect after hearing the continuous tone key in the correct tariff figures.

A new Payphone from British Telecom

Many small businesses would like to provide their customers or visitors with the use of a telephone but cannot afford to give away free calls, while other businesses may want to control their staff’s use of the telephone. Households may want to cut down on heavy telephone bills by ensuring everybody pays as they call.

Renting a payphone may be the answer, but the current models are not ideal for every situation, so British Telecom is to introduce new kinds of payphones exploiting the latest technology. The Table-top Payphone is one of these and offers two major benefits:-

  • it is a compact, attractive payphone designed to sit on a desk or table-top,
  • it can either be simply and permanently a payphone or, at the turn of a key, it can be switched by the renter from a payphone to an ordinary telephone and back again.

When it is used as a payphone:-
Local, trunk and international calls may be dialled (calls to or via operator services are not possible except for 999 access - the renter can obtain operator access by switching to ordinary telephone use);

it accepts 2p, 5p, lop and 50p coins in a single coin slot, with little pressure needed to insert them;

up to 4 coins may be inserted in advance, with further coins added during the call;

unused coins are returned (no change given);

full incoming service is available except for inland transfer charge calls.

When switched to ordinary telephone use:-
Full facilities are available, including operator services, without the need to insert coins.

To Use the Payphone

  1. 1. Lift handset. The red lamp will flash.
  2. Insert coins before dialling, up to at least the Minimum Fee (but: no more than 4 coins should be inserted at the start of the call). If you intend to use a 50p coin, insert small value coins before the 50p so that the payphone does not cash the 50p if you have the wrong number or the person you want is not there. The Payphone 100 refunds wholly unused coins. IT DOES NOT GIVE CHANGE.
  3. Dial the number. As soon as the call is answered, the payphone will cash enough coins to pay the 8p minimum fee, in the order in which they were inserted.
  4. Add coins during the call if you need to. Just before all the coins are used up, the red light above the press buttons will flash and you will hear a tone. If more money is not added, then the call will be disconnected.
  5. Replace receiver at the end of the call, and the payphone will refund any un-cashed coins.

We hope you will like this new payphone from British Telecom. If you have any questions - about ordering for example (this payphone will become available in Autumn 1982 at a rental of around £20 per quarter - this is in addition to the exchange line rental), please contact:-
British Telecom ICS2.2.3

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Last revised: December 06, 2010