Optional Components

Telephone No. 706 Accessories
By Sam Hallas

To round off previous articles on the Telephone No. 706, this article looks at some of the accessories for use with that novel telephone from the 1950s and 60s.

Cord & Block Terminal
As stated in previous articles, nearly everything about the Telephone No. 706 was new.  We saw the new handset cordage in the article on the Handset No 3. The desk cord and block terminal were also new designs.

Fig 1a - Green cord & Block Terminal No. 30 Fig 1B - Red cord and Block Terminal No. 52A

The initial cords were three-way to allow an extension bell but no more.  For extension plan working a four-way cord was needed and this became standard later.  Fig 1a is a three-way cord and Block Terminal No. 30. Fig 1b shows a four-way cord (Cord Instrument 4/88) and the, by now, more common Block Terminal No. 52A.  The cord and block terminal were supplied in colours to match the telephone body.

As on the handset the new cordage does away with the need for tie strings by using a moulded grommet glued to the cable sheath.  The wrapped wire loops used in the past are replaced by the simpler and cheaper spade tags.  Replacing a damaged cord is much quicker with the new type.

It is my opinion that the Post Office exercised tight quality control over the quality of the plastics used in the cords and grommets.  The ones I have are all between 25 and 45 years old, yet none have gone slimy and sticky.  Some non-PO ones in my collection have deteriorated like that.

Accessories - Press switch, Switch No. 5A-3

Fig 2a - Telephone No. 706 with button marked 'Press'
Fig 2b - Switch mounting
The switch is mounted in it's own metal mounting which fixes into a slot in the switch hook frame and then finally fixed by the smaller screw located to the left of the dial fixing screw.

Fig 2a shows a Telephone No. 706 with a recall button marked 'Press'.  In Fig 2b you can see how it mounts onto the phone and fixed by the screw located to the left of the dial mounting retaining screw.

The button here is labelled 'Press' suitable for recall or call exchange on a shared service line.  A different option button labelled 'On/ Off' can be used for a bell off function and it works by having an additional foot to its rear arm.  In Fig 3, this button is show to the lower right and by pressing the 'on' side of the switch causes the button to tilt sideways, so that it latches in the operated position.  Pressing the 'off' side of the switch causes the switch to tilt the opposite way, thus releasing the latch and the button springs back up.   Simple and clever.

Fig 3 - Different press buttons


Additional Hookswitch Springset

Fig 4a - Additional springset
Fig 4b - Springset mounting - the two fixing screws can be easily seen on the switch hook upstand

There are applications that require more contacts to be operated when the phone is off-hook than are provided in the basic circuit.  A typical case is on extensions connected to a Switchboard PMBX 2/..  Fig 4a shows a springset 1/DSP/1252 which has a single make contact.  Fig 4b shows one in situ in a phone that was a PMBX extension.  It fits on the right hand support pillar and operates in the same way as the main springset on the left hand pillar.  Other springsets with different contacts were produced.

Buzzer No 32A

Fig 5a - Buzzer No 32A-1
Fig 5b - Buzzer in situ

This is a small DC buzzer used, typically, on extensions on a Plan 105 or 107 to allow the main to buzz the extension on an intercom call or to transfer the exchange line.  It mounts using one of the bell screws as seen in Fig 5b.  It looks like a tight fit, but there is room to get the case back on again - just.

Rectifier Element No. 205A & Thermistor No. 1A-1

Fig 6 - Rectifier Element No. 205A (black item in centre of picture)
Fig 7 - Thermistor No. 1A-1 (black and yellow item)

Rectifier Element No. 205A (Fig 6) consists of two diodes connected back-to-back - that is with the anode of one connected to the cathode of the other.  It's purpose is to limit voltage surges to the receiver in order to protect the user against acoustic shock which could damage their hearing. It is fitted directly to terminals 1 and 2 as seen.  Initially it was provided as an accessory but later it was fitted as standard as a routine safety measure.  The style of construction varied by manufacturer.  Some were in hard cases with moulded in spade terminals.

Thermistor No. 1A-1 (Fig 7) was generally used on shared service lines (party lines) to prevent bell tinkle when the other party was using the phone.  It was wired in series with the bell, replacing the strap between terminals 16 and 17.  The Thermistor has a high initial resistance preventing the bell from ringing.  After a short burst of ringing current it warms up so that its resistance reduces sufficiently to allow the bell to ring.  It always seemed to be the practice to push the Thermistor into the U-shaped cutout in the regulator to hold it firm.

Please note that the phone in Fig 7 is fitted with the additional springset and so it has an extra wire in the desk cord, coloured orange.  The Thermistor is only fitted to show where it would fit - it was not there originally.

Lock No. 29
When this lock is switched on it only allows 999 calls to be dialled.  A Dial No. 28 must also be fitted.


Wall Hanging Adaptor

Fig 8a - Wall Conversion kit
Fig 8b - Telephone No. 706 hung on wall

The wall telephone in the 700-series, Telephone No. 711, was not available immediately.  As some sort of stopgap this adaptation, right, was issued as Telephone No. 1/706, a rebadged version of Ericsson's N1065.  Some private suppliers used the kit shown in Fig 8a to make wall telephones available without increasing their inventory by stocking the Telephone No. 711 separately.

The T-shaped bracket is fixed to the wall. The Telephone No. 706 has its dial and outer number ring reversed and its feet removed.  The case fixing escutcheons are removed and replaced with the chromed bracket.  The telephone can then be hung from the top of the T-bracket and fixed with the screw at the bottom.

Other Accessories

Several other accessories were available and are listed below and in Diagram N808.

These include:-

  • Local battery adapters comprising an inductor and two different extra springsets.

  • A dial dummy for use on CB and Local battery versions.

  • Additional connection strips, 6-way and 18-way.

  • Additional 2uF capacitor.

  • A watch receiver.

The list is proof, if proof were needed, of the versatility of the 706 design.


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Last revised: November 05, 2022