GPO telephones
The General Post Office (GPO) of the United Kingdom carried the sole responsibility for providing telecommunication services across the country with the exception of Hull.
[1] During the early days of telephones, in the UK, a variety of instruments were produced, in low volume, often combining new and emerging technologies with the traditional skills of the wood joiner and cabinetmaker.
The Type 121 had the transmitter mouthpiece screwed onto the front of the box and the switch hook, holding the receiver, protruding from the left hand side.
This made it a true, one-piece telephone which was available either 'stand alone', mounted on a handsome, wooden, back-board, with integral writing desk or, as a Tele.
The transmitter (microphone) was of a very poor, carbon granule construction, which absorbed moisture and required regular replacement.
This was initially the wooden cased version shown or the later, compact, Bakelite, Bell set 25.The 162 was originally launched in 1929 as the last of the 100 series.
When this system was eventually revisited and brought up to date, with the 700 series Plans 105 and 107, the equivalent control unit was dubbed 'The Planset'.
The term ASTIC indicates the use of an anti-sidetone induction coil, to permit only a small, controlled amount of speech signal back to the talker's ear to provide necessary sidetone for a natural communication experience.
As these were banned by law from connecting to external lines, they contented themselves with producing systems for automatically dialling between company offices, within the same building or, via private wires, rented from the GPO, virtually anywhere.
All these bellsets appeared identical externally, with a contoured, moulded cover which looked stylish alone, but would dock firmly underneath a 232.
They were all based upon the same baseplate but differed in the type of bell and whether this was alone or accompanied by a capacitor, and / or an induction coil and any other telephone circuit components and wiring.
Electrically identical to Bellsets 26/56 but with an all-weather case and externally mounted bell gongs, for use where much more volume was required.
The 700 series was the GPO's response to public demand, fuelled by American television shows, for a modern design with a helical, anti-tangle handset cord.
Again, still also available in CB (no dial) form, it was a robust design which is still in use today in the UK, suitably modified for use with the New Plan BT sockets.
The purpose of the regulator was to vary the amount of AC speech current flowing through the transmitter and receiver, to prevent it being considered too loud by subscribers on short lines.
Whilst most of these phones were superficially similar to the GPO 706 many had different internal parts including "tropicalised" versions for countries with high humidity or potential insect ingress.
710, 746, the 711/741 wall phones, pendant telephones, headsets, re-styled bellsets, connection blocks and distribution panels.
Incredibly, two of the knockouts could wind up, for a full system, containing two pushbuttons each, one for each of the other four stations, L-shaped to cram them into the small holes.
(see above) Initially with the 700 series, when a subscriber (customer) ordered a wall-mounted telephone, the attending fitter would have to requisition a standard Tele.
The GPO introduced the Trimphone in the late 1960s as an alternative to its standard telephone, this new phone featured a distinctive warbling ring as opposed to the traditional bell.
Push-button models were introduced in the 70s and the final version of the Trimphone was the Phoenix phone, available in a range of new colours known as The Snowdon Collection which came in out 1982.
It used a DC signalling system comprising a number of rectifier diodes[4] arranged in different polarity configuration according to the button pressed.
fuelled by US television shows, so the advent of 'Touchtone Dialling' in later American TV output brought about a demand for the same at home in the UK.
Completely ignoring the then-standard US layout, an experiment was put into motion at the Dollis Hill Research Centre.
The push buttons just created the same loop disconnect signalling pulses as a dial telephone, which caused horrendous post-dialling delay and much knuckle rapping frustration.
With its case removed, the master instrument was then screwed down onto the Planset whilst squeezing a thick umbilical cable up through the oblong hole in the telephone baseplate.
The hole left in the rear of the telephone case, by the removal of the, redundant, instrument cord, now had to be filled with a matching coloured, square bung.
With the advent of 'New Plan' sockets and changes in legislation, subscribers were now free to either rent their telephone or purchase one from any source (as long as it was an approved model).
This was addressed by the simple inclusion of a steel bar in the handle of the handset to give it weight and make it feel a 'serious' piece of equipment.
This telephone is not a domestic instrument but one of many designed for use on early electronic office systems, with ten direct-dial extension buttons.
