The BT Response 300 is a modern processor controlled, combined push button telephone, single tape answering and recording machine with remote interrogation. The instrument cannot be wall mounted although a plinth, purchased separately, may be available in the near future.  The recording media is a MC60 Micro-cassette.

The facilities for the instrument are as follows;

Signalling is switchable by the customer between tone-earth, tone-time-break, (100mS) or loop-disconnect. Operation of the "*" key when in loop-disconnect mode will change to tone signalling for the duration of the call.

Last number Redial:
and "#" count as one digit and the pause counts as two digits.

Call progress monitor with LED indication.

Latching Secrecy Button with LED indication.

Dial Pause, 4 seconds:

Memory Stores: 3 one touch and 10 indirect (1 to 0 under keypad). Up to 16 digits including "*" and "pause": The "*" counts as one digit, the "pause" uses two digit locations.

Memory stores are protected by line power and will be retained for 5 minutes if mains power is disconnected.

Time/Day announcement:

Message Tape: Standard MC60 Microcassette. Up to 30 minutes recording time.

Announcement: May be up to 2 minutes duration.

Memo: Up to 30 seconds with separate LED indication, replay and pause facility.

Message indication: The PLAY LED will flash if a message is waiting and the display shows the number of messages received.

LED display: If the Response 300 is not set to answer calls the LED will display a dot.

Playing messages: Press Play, Response 300 announces the number of messages stored followed by "please wait" as it rewinds. The messages are played back through the loudspeaker while the displays shows "P". At the end of each message, the time and date of the recording, which is held on tape, is announced.

Saving messages: During playback, pressing play will save the message and skip to the next message. At the end of message play, Response 300 will announce "that was your last message" and the display will flash "-" for four seconds. During this period, all messages may be saved by pressing save.

Play all (recovering unsaved messages): If Response 300 has been reset without the messages having been saved, Response 300 will announce "you have no messages" if the play key is pressed. However following this announcement the display will flash "-" for four seconds, if the play key is operated again during this period Response 300 will announce "please wait", rewind and replay all messages which have not yet been overwritten.

Pause: Press Play. The display shows a flashing To continue press play again, the display changes to PI.

Message save: Press save after listening to the messages.

Automatic Message Save: When accessed remotely.

Incoming Message: Up to 3 minutes. Up to 32 digits, including "*", "#" and pause.

Skip Announcement: Frequent callers can key "*" from a Touchtone telephone or remote controller and leave a message without having to listen to the announcement.

Message counter: Displays the number of messages received and displays"." to confirm power is on. If more than nine messages have been received, the display will change from a steady 9 to a flashing 9.

Volume Control: Located on right hand side of instrument.

Call Screening: With the volume control in the mid-position, it is possible to listen to incoming callers leaving a message. If it is desired to speak to the caller, the recording should cease when the handset is lifted. If this does not happen, briefly replace the handset or press the Answer key.

Two way recording: To conform to regulatory requirements, a security tone is heard at 15 second intervals.

Fast forward and rewind facility:

Ring Adjuster: 2, 6 or TS (Time Saver). TS = Answers after 2 rings if messages have been left, or 6 rings if no messages. This facility aids remote access. i.e. When accessing remotely, if the call is not answered after 2 rings, the caller can clear down knowing there are no messages and save the cost of a call.

Remote set to Answer: Call Response 300, let it ring 20 times, listen to the announcement and hang up.

Branchphone reset: Will release machine from the line should a parallel telephone handset, or it's own handset be lifted. Inhibited for a short period (1 second) before and after answering.

Remote access with a preset 2 digit security code:

Announcement library: The customer may keep a library of tapes which have been pre-recorded with different announcements. The mains power to the Response 300 must be switched off and on after the tape is changed for correct operation. The time and date should then be reset.

Made by Inventec Corporation.

Distributed by BT Sale and rental. BT UK Trade Sales, sale only.

Approval Number S/2981/3/P/502807
Approved DEL, PBX CAT 1, 3, 5 & 7.
Approved as supplied for connection to Public Switched Telephone Networks (PSTN) and 2-wire PBX extensions.

Unapproved modifications must not be carried out on this machine, to do so would invalidate approval making connection to the PSTN unlawful.

User Guide TPU 1881
Phone in card TPU 1881A
Product Manual PDM/TPM/A010

A Phone Socket and a 240 volts, 13 amp, 50 Hertz mains supply socket are required within easy reach of the instrument. Transformer lead and Line Cord both measure 300Omm.

Suitable for use on Phone Socket installations on DELs and most types of 2-wire PBX extensions.
Ringer Equivalence Number (REN) is 1.

The User Guide supplied gives sufficient information to install and commission machines at phone socket installations. MAINTENANCE
The instrument does not contain any on-site serviceable parts, therefore maintenance is limited to functional testing, checking the facility switches are set to provide optimum performance of the instrument to match the line to which it is connected, the condition of the tape and that the tape head is clean.

If the machine fails completely, the output voltage of the Transformer should be checked. The Transformer output is marked 9.5 volts dc, but will measure about 13 volts when tested with the output open circuit.

The User Guide recommends that the customer should perform the following routines;
Every three months, turn the tape over and re-record the announcement.
Every six months, clean the tape head, capstan and pinch wheel using a cotton bud moistened with a proprietary tape head cleaning fluid.

If the tape is worn, it may be replaced with any high quality "normal bias" MC60 size Microcassette. Although available, longer and shorter tapes must not be used as they will prevent the instrument from operating correctly.

The duration between the above routines should be reduced if the machine is heavily used.

Response 300 may be accessed remotely from any Touchtone telephone or by the use of a remote controller.

Accessing messages: Call the Response 300 and wait until it answers the call. During or after the announcement,- operate the # key on the telephone or controller. Two beeps will be heard. From the keypad, enter the first digit of the security code, Response 300 will beep once. Enter the second digit of the security code, Response 300 will beep twice.

With the correct code entered Response 300 will announce the number of messages received and announce "please wait" while it winds to the correct position on the tape.

Should an incorrect code be entered, a second attempt may be made, if this is incorrect, Response 300 will hang up.

Memos and messages will be replayed automatically. Message replay will pause every 2.5 minutes and a pause tone will be heard for several seconds. During remote access, keying digits from the keypad or remote controller will allow the user to control the functions of the Response 300. See the user guide for a full explanation of the facilities.

Unless messages and memos are reset remotely, they will be saved automatically.

New units carry a 21 months warranty from the date of manufacture as shown on the year and week marking on the base of the instrument. These markings form the first 4 digits of the serial number.

BT guarantee sold machines (excluding cassette tape) for 12 months from the date of purchase irrespective of the date of manufacture.

On-site maintenance of the Response range is limited as the equipment contains no serviceable parts. Some routine servicing - detailed in the User Guide should be carried out by the customer, but field maintenance is restricted to checking the facility switch settings and testing the power unit output.

Several adapters used with Response instruments are marked with lower outputs than those actually measured. Approximate voltage readings (with the output open circuit) are as follows:-
Transformer 19B (marked 13.5V DC) measures 19 - 20v.
Transformer 752 (marked 9V AC) measures 11 - 12v.
Transformer 753 (marked 9.5V DC) measures 13 - 14v.


Description						BT Item Code
Response 300 Combined Telephone / Ans & Rec Machine	870627
(Complete with transformer and tape)
Transformer 9.5 volts dc: Black				870471
Transformer 9.5 volts dc: White				870629
BT Remote Controller No 2 (MF4)				870427
Message Tape MC60 Microcassette.			870435
Or any high quality, normal bias MC60 tape

Normal test conditions when waiting to answer. After answering, the telephone and answering machine presents a loop resistance to line of approximately 328D measured at 28mA. Additionally, the instruments will draw about 4.6gA on hook. This may appear to give apparent 'Low Loop' line test conditions. With the handset off-hook, like many modern telephones, they may give high resistance telephone loop test conditions.

15 seconds to 2 minutes depending how many messages are recorded.

The ringing circuit has been designed to recognise both PSTN and all internal ringing cadences generated by BT PABXS. There is no manual ring facility.

3. VOICE / TONE DETECTION (Voice Operated Switch - VOX)
The VOX will release the machine from the line after approximately 4 seconds of quiet, constant or cadence Network tone (i.e. dial tone, NU etc).

4. CLEAR DETECT Line Break Clear / Release from line.
Modern exchanges generate a 100 ms line break on the called parties line when the calling party clears down, this is a called a disconnect clear signal. The machine will detect this signal and immediately release from the line without the need to wait for network tones.

This facility causes the machine to release the line when a telephone connected to the same line is taken off-hook. For about 1 second before and after answering this facility is inhibited. This prevents the false release of the machine from line due to line 'ringing' (current surge to & fro) when answering.

The handset and keypad are line powered. The answering / recording features of the instrument is mains powered from the 9.5 volt dc plug top transformer.

In the event of a mains failure all mains dependent facilities cease to function. Provided that a valid announcement has been recorded, restoration of the mains supply will automatically reset the machine to answer whether or not it was set to "answer" before the supply failed.

This is a system default condition and cannot be overridden. Messages received before the power failure are not lost and can be played back remotely or by using the play button on the machine.

The cassette cover which is located under the memory label, must be in place for the Response 300 to make and receive calls.


It has been reported that a large quantity of the Response range of TARMs have been returned as faulty without being fully reset and retried. Some faults are caused by quick line disconnects and Radio Frequency Interference and may be cleared by a reset.

Models such as the Response 200, 300, 400, 500 & 1000 have all got a reset button on the underside of the unit. Depressing this button momentarily, using a small probe, will perform a slightly different reset to that performed when the mains is turned off/on. It is suggested that this is performed first, then retry all facilities, before changing out the unit.

However, if after changing the unit the same fault recurs on the new unit, the problem may be site specific and changing the unit again will be of no advantage. If this is the case, please contact the Technical Helpdesk for further advise.

A major problem with Response TARMs recording after a message has been left has been caused by the exchange equipment presenting 'clicks' on the line when it is idle. This is due to a modified line card on System X exchanges. BT Labs are aware of the problem and are investigating a cure. Changing the unit will not clear this problem. 

This problem is commonly reported as 'not recording messages' or 'message counter not incrementing after messages left'.

This problem only appears on Response 300 units connected to exchanges that give an 'end of call signal'. It is this signal which has been the cause of Response 300s ignoring valid messages of a very short length (typically less than 4 or 5 seconds). As a result, the answering machine will reset without either recording the call or incrementing the message counter, although it may appear the message has been recorded.

The Response 300 also suffered from a problem of memory loss if the power was disconnected even for a short while. Documentation states that the unit should hold its memory for up to 4 hours. The problem was due to a component change in production but has now been resolved by producing a modified instrument.

Both of the above problems have been cleared in units with serial numbers greater than 9426093469 which should be available by the end of August. These units will also have a red rectangular label attached for easy identification. 

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Last revised: October 30, 2022