BPO 300 TYPE TELEPHONE INFO
BPO 300 TYPE TELEPHONE INFO
Quick History
Around 1930 the Swedish Ericsson company decided that a new telephone shape was required which would have a global
appeal - they considered that the world was their marketplace (and quite rightly still do so!). The job was given to a
company engineer of Oslo's Elektrisk Bureau (an Ericsson subsidiary) called Johan Christian Bjerknes. He decided to use
Bakelite, but found that he needed help with the design. The leading Norwegian artist Alf Rolfson was at the time too
busy with another project and so the job was given to Jean Heiberg.
Jean Heiberg (1884-1976) was a Norwegian painter who had studied in Munich and in Paris, latterly under Matisse. At the
time he had just returned from Paris to take up a post as professor in Oslo's National Academy of Arts.
His final design had hard lines and sharp edges (possibly influenced by the 1930's Cubist movement) and retained
elements of the neo-classical stylobate which dominated his first plaster drafts.
It went into production in 1932 as the 'DBH1001' and later the Swedish Telephone Co (Televerket) adopted it as standard.
The Prince of Wales (Eldest son of King George V) visited the Stockholm Exhibition in October 1932 where the telephone
was displayed. He admired it and selected it for use in his home. The approval of this fashionable man-about-town did
much to promote the telephone's success beyond Scandinavia.
Around that time the BPO wished to introduce a telephone with integral bell. They developed the Tele 332 in conjunction
with Ericsson Telephones Ltd (UK). By 1937 there were six presses in England stamping out the Norwegian painters
designs. This also came in a standard colour Black, although again other colours were available including Lacquer Red,
Jade Green and Ivory - and many other colours have been spotted - but beware of sprayed cases!. The 300 Type Tele used
the Tele No 164 Handset and had new internal equipment. A variety of different instruments based around this design was
produced to suit varying purposes.
The 300 series was not intended as a replacement of the '200 type' instrument it was still thought that a separate bell
mounted centrally in a household would be more desirable (indeed the 200 type was used into the 1960's for certain
applications!). The 300 type was thought to be primarily suitable for business use.
The 300 type series contained an integral bell, catered for the provision of 1, 2 or 3 keys (with interchangeable
labels) and was easier to manufacture because a single moulding for the case was used rather than several for the '200
type'. Ease of fitting and subsequent reduction of fault liability was a by-product because there was no need to drill
holes in walls for mounting Bellset etc and no wiring to connect for the external Bellset.
All of the main manufacturers produced 300 Type sets, both for the BPO and their own private systems. Another common
manufacturers code seen on the handsets of these instruments is 'AEP' - these were manufactured not in England but in
Portugal by 'Automatic Electric Portugal'.
ARTICLE BY ROB GRANT
Suggested further reading:-
The Conran Directory of Design' edited by Stephen Bayley.
Telephone Design Notes for Students - Design Museum
IPOEEJ Vol. 31 page 1 - see below
THE POST OFFICE ELECTRICAL ENGINEERS’ JOURNAL
Vol. XXXI - April, 1938
The New Combined Hand Microtelephone and Bell Set
Part 1
by C. A. R. PEARCE
A new telephone is described in which the telephone instrument and bell set are combined in the same moulded case.
The advantages claimed are ease of fitting and reduction of fault liability. Provision has been made for one, two or
three press buttons to be mounted on the instrument, thus permitting a variety of extension and interconnection
facilities to be given.
There has recently been developed by the Post Office Engineering Department, working in conjunction with Messrs. Ericssons Telephones, Ltd., a new standard subscriber’s set in which the bell, condenser and induction coil are mounted as an integral part of the telephone instrument and not as a separate bell set as hitherto.
When the Telephone No. 162 was introduced in 1929 it was considered that the demand for a combined set, i.e. one in
which the telephone and bell set form a single unit, would be insufficient to justify the development of a special piece
of apparatus and consequently the only provision for such an item was the arrangement whereby the standard bell set (No.
25) intended primarily for wall fitting could also be mounted under the telephone. Experience has shown, however, that
even with such an admittedly makeshift arrangement
as this, approximately half the micro-telephone instruments are fitted as combined sets and doubtless with the new
design an even greater proportion of the demands will be for this class of instrument.
There is, however, a serious
disadvantage in combining the bell with the telephone in residences where the bell has to be heard in all parts of the
house. In such instances the best position for a bell is in the hall, whereas the telephone may be anywhere that is
convenient. For this reason the new set is regarded as being primarily suitable for business subscribers and plan number
installations, although its use is not, of course, restricted to these spheres.
The advantages of combining the telephone apparatus in a single unit are, first, the economy of a single case and chassis as compared with the variety of mouldings which make up the Telephone No. 162, and, second, the ease and simplicity of fitting. With a single unit the fitter has, on direct exchange lines, to connect only two wires to the block terminal and need not open up the instrument to do so. Thus the new instrument materially reduces the possibility of errors in fitting. Its use will also generally reduce the disfigurement to walls which is occasioned by this operation, since the block terminal can frequently be located on a window-frame or skirting board and the fitter thus saved the plugging of the walls. A very prolific source of faults is bad fitting and the combined set is well suited for fitment by relatively unskilled staff.
General Design
Although the external shape is based on that of an instrument designed by the Swedish Ericsson Co., the internal
arrangement is entirely new. The design of the case is centred around the use of a plastic moulding and the result is
considered to be an extremely sturdy construction and ideally adapted for production in large quantities and in colours.
The mould from which it is produced is practically a straight 'draw-out', the only loose part being that which forms the
dial aperture.
It will be appreciated that an important factor in the success or failure of any design of telephone instrument is the reaction of the general public to its external appearance. It is thought that the new set will be popular on this account as it has already received very favourable comment from many acknowledged authorities on design and was especially selected by the Duke of Windsor when Prince of Wales during his visit to the Stockholm Exhibition in October, 1932, for use in his own private residence.
The original design did not include the
sliding tray in the base and it can hardly be claimed that this addition has improved the general appearance of the set.
This tray was designed as a convenient holder for the list of "dialling codes“ in those areas where a subscriber obtains other exchanges
by the dialling of two or three routing digits, but it has been decided to provide it on all telephones as a container
for a subscriber’s private directory.
The shape of the
Handset Micro-Telephone (H.M.T.) rest has been designed
so as to facilitate the removal and replacement of the hand microphone and it is anticipated that the use of the button
type of “switch-hook,” in lieu of the pattern used in the Telephone No. 162, will obviate the
With the exception of the dial all the various
components are mounted on a single chassis plate. The condenser is the only component for which it has been
found necessary to introduce a special variety on account of the new set. Advances in the technique of condenser
manufacture have made it possible to produce a 2 + 0.1 uF condenser which
The layout is such that all the main component
s with the exception of the switching springs and dial are revealed
and made accessible for maintenance operations by the removal of the under-base, while the removal of three further
screws frees the chassis from the case and enables any maintenance work on these two items to be easily carried out.
Every effort was made to render the dial directly removable from the front of the instrument but this has not been found possible
without spoiling (the appearance of the set.
The circuit of the CB and Auto type is simply the standard anti-sidetone arrangement (Coil Induction No. 22) which has been described elsewhere. The local battery circuit remains a sidetone arrangement and is practically the standard three winding induction coil circuit as at present used when a Telephone No. 196 is connected to a Bell Set No. 31. Although the local battery set will eventually disappear as subscriber’s instrument it will still presumably be necessary for private wires, etc., and it is likely that for these uses a local battery anti-sidetone induction coil will be introduced, but no entirely satisfactory design of coil is yet available. Space has been left, however, to permit of the use of any design of anti-sidetone coil which can be envisaged at the moment.
A feature of both C.B. and LB. circuits, which is novel to subscriber’s
sets in this country, is the shunting of the transmitter by a 0.1 uF. condenser.
This condenser, besides preventing the rectifier action of the transmitter from causing interference between the telephone and nearby radio sets and vice versa, also has the effect of reducing the likelihood of the transmitter becoming packed by current surges occasioned by automatic switching, etc. A filter for preventing the dialling impulses from causing radio interference has also been designed and it has been arranged that, when required, it can be connected directly to the dial strip terminals.
There are in all some seven main
Controls for Extension Instrument Installations, Plan Number Working
One of the main features of the new instrument is the facility for accommodating on the telephone the controls for
plan number working. This facility has for some time past been a feature of the telephone instruments used by certain
continental administrations but the design of the British Post Office apparatus has not until now been such as would
permit of the easy inclusion of switches and keys, etc. The whole of the facilities necessary for the existing plan
numbers (excluding Nos. 5 and 7) as well as many others are provided by means of three key units, two of which are
identical except that for economy one is equipped with just sufficient switch springs to meet the more popular of the
plan number arrangements, whereas the other is equipped with enough springs to deal with all anticipated demands. The
third key is fitted with one make contact only and is mounted and wired as an integral part of one particular variant of
telephone, important uses of which will be as an extension instrument for P.B.X’s, where the press button will be used
for transferring calls.
There
are several distinct advantages both to the subscriber and to the Post Office which are obtained by locating switching
apparatus as part of the telephone. For the subscriber it simplifies operation and for the Post Office it simplifies
fitting and enables the instrument to be prepared at the fitting centre complete with keys, terminal block, etc., ready
for wiring. The labour economies possible from such an arrangement are obvious.
The convenience of this form of control and the fact that it may be linked
with the switch-hook operation (switch hook release feature) has made possible considerable improvements in plan number
facilities and it is anticipated that a complete revision of these will be undertaken
in the near future together with the
introduction of a simple house exchange system catering for tip to three extensions with exchange line facilities. The
switch-hook release feature is of particular importance because of the
A further economy to be introduced with this set is the standardisation of the label, it having been found possible to meet all the envisaged demands for plan number working by ten varieties of engraved label. Up to the present the labelling of keys on plan number installations has been carried out with mechanically engraved xylonite labels mounted adjacent to time keys. The new labels are a chemically engraved metal type of rather neater appearance than the old pattern and cheaper to produce.
Key Units
The two key units are of similar appearance of which one consists of three plunger-type keys
These facilities are all controlled by means of time
very simple control plate shown in the picture to the right. The key when operated is held in position by the lip of the
spring latch plate meeting time projection on the key in ratchet and pawl fashion. The depression of a second similar
button will, of course, force out the latch-plate and release the first button. To render any key non-locking,
therefore, it is only necessary to prevent the latch-plate from overlapping time key projection. This is done by filling
the lip with a portion of the control plate. The arrangement is such that the control plate may be mounted in a
Switch-hook release is provided by removing a second control plate
from the key frame where it is located for convenience and attaching it to time switch-hook mechanism of the telephone.
The sloping face forming the underside of the top projection on the plungers has been provided to cater for cases where
the subscriber inadvertently depresses two locking buttons simultaneously and where the conditions are such that there
is no other means of releasing them. To obviate this the top lip is designed so that if either button is depressed
beyond its locked position it will force the latch plate outwards and release time second button.
The key unit switch springs incorporate twin contacts and arc mounted
vertically to reduce fault
Conclusion
The new telephones and keys offer what are, in the writer’s opinion, unique facilities for
mechanical switching associated with the telephone and facilities, moreover, which could only otherwise be provided by
complicated lever type keys or by press buttons with relays, either of which arrangements would indubitably be
considerably more expensive than time new system, and it is considered that time new apparatus represents a real advance
in telephone instrument design.
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Last revised: 30 November, 2003
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