In practice the unit was normally left in circuit. The downside of this plugin module was that if the telephone was dropped or mishandled the regulator board would become loose and fall out and cause the telephone to stop working until it was replaced by a technician. Compare this with the inside of a 746 where the regulator was integrated into the main circuit board. The early extension instruments were also 200 Type telephones, mounted on a Bellset 39a or 44; but these were modified to remove the switching mechanism and contained an integral bell for exchange line signalling when the exchange was switched through to the extension and a buzzer for intercommunication signalling from the main. GPO Tribune Blue base. A switch on the left hand side changes from Loop Disconnect to MF4. Also shows the wheel which is a crude method of adjusting the ringing volume This was a 746 type telephone which could transmit MF4 signalling, also known as DTMF touch tones. These telephones could only operate to exchanges that could deal with MF4 but they were used on PABX systems that used MF4 for internal calls from the 1970s. The TXE1 exchange could handle MF4 calls as early as the late 1960s. This was however a unique prototype exchange, which served customers in Leighton Buzzard: otherwise customers did not have access to MF4 capable exchanges until later models of the TXE4 system came into service in the late 1980s. No. 740 are provided by removing the dummy button and fitting a Part 1/ ... 10/DBU/372 using the pin, Part 1/DPI/203, provided in the telephone.

No. 746 is fitted by removing the dummy button and clip and inserting a Part 1/ or 2/DBU/362 which is retained by two pins, Parts 1/DPI/203. When two press-buttons are required, two Parts 1/ ... 6/DBU/363 are fitted, each with one Part 1/DPI/203. This article's lead section may be too short to adequately summarize the key points. Please consider expanding the lead to provide an accessible overview of all important aspects of the article. ( May 2021) These were updated versions of the 200 type plans 5 and 7 but based on the 700 type telephone. It had a master station which was a 700 type telephone mounted on a plinth with buttons, 'The Planset 625'. The master station and the extension stations could call and speak to each other and also handle and transfer outside calls. The difference between a Plan 105 and Plan 107 was that the latter had only one extension; the former had two. On plans with the 'A' suffix, conversation between the extension and the exchange was private against the planset. On a Plan 107 both of the long buttons, on the front of the Planset 625, were connected together. Pressing either would 'buzz' the single extension. Inside the circuitry is different in that the regulator components are soldered directly onto the printed circuit board, the switch-hooks and other components were miniaturised. No conventional wiring version was produced. The same colour options as for the

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Nos. 740 and 746 shows one change from that of the Telephone No. 706. The brown wire from dial terminal D3 is taken to telephone terminal T3 instead of gravity spring 5. This short-circuits the transmitter when the dial is taken off-normal and prevents surges in the spark quench circuit passing through the transmitter. These similar telephones were initially only loop disconnect types, when introduced in the early 1980s, but were later available in MF4 (touchtone) versions. They were among the first range of BT phones to be available for outright sale. A novel feature of these phones was that both the dialing circuit and the transmission circuit were on a single microchip. The one shown in the photograph is a 9003R manufactured in January 1984 and is loop disconnect. The Tremolo has squarer, flatter styling with a handle recess in the case, below the handset, by which it may be carried in use. An 'off-rest' position is provided with the handset resting across the instrument just above the dial.

Cromwell's laws so issued a very similar act in 1660, which confirmed the formation of The Post Office. The law made the GPO This was the same as a 706 but had four possible buttons or lamps fitted at the top of the case. Dummy buttons were used where neither button nor lamp was used. The telephones can be modified for a variety of uses by the fitting of add-on units, adapters etc. and these will be described in later instructions.The original GPO Telephones were produced by the General Post Office in the UK from the advent of the telephone in the