|These are extracts from the minutes from the British Telephone Technical Development Committee,
Subscribers Apparatus Development Sub-Committee meetings which were held every 3
months. These were run by the GPO and held on their premises. The
GPO contractors also attended these meetings. The minutes started around
1942 and finished in December 1967 due to the re-organisation of the Post
The minutes on this page show the development of the Headset No. 1.
SCP No. 69 - Operators Combined Headset
11th July 1956
Mr. Cameron (GPO) stated that the development S.C.P. would be issued when the
design objectives had been decided; this, it was thought, might take some time. Col. McMillan said that P.O. Research Branch was attempting to determine the
desirable transmission performance (sending and receiving) to be achieved by a
new operator's instrument. He added that the P.O. would welcome any opinions
that the manufacturers might care to advance on this subject. When transmission
performance figures had been settled, R. Branch would then proceed to specify
detailed design objectives for receivers, microphones and induction coils. Receivers of general characteristics similar to those of the "Medresco" external
receiver (used with the National Health Service Hearing Aids) would probably be
chosen leaving only the microphone and induction coil for detailed
6th October 1948
Mr. Cameron (GPO) stated that although the design objective had not yet been
completed, progress was being maintained. The Chairman drew attention to the
statement made at the last meeting to the effect that the P.O. would welcome
any pinions that the Manufacturers might care to advance on this subject and
asked if any wore likely to be forthcoming. Mr. Smith replied that the matter
remained under consideration.
12th January 1949
Mr. Warren (TAC) stated that the Manufacturers& comments had been forwarded to the
P.O. on 3rd January 1949. Mr. Cameron (GPO) confirmed this and said that as the design
objective had not yet been determined it was still not possible to issue a
development C.P. at this stage; there was however, every prospect of one being
issued in the future.
13th April 1949
Col. McMillan (GPO) said that this matter was not
sufficiently advanced to warrant the issue of a development C.P. at this stage.
13th July 1949
Col. McMillan (GPO) said that a Research Report, ,which would add to the information
on this case, was in course of publication. The Chairman stated that when this
was available it would be issued for information as an addendum to the C.P. Col.
McMillan (GPO) said that the time was not yet ripe for making the CP a development
case but the Research Report provided data from which it would be possible to
formulate target specifications.
11th January 1950
Mr. Cameron (GPO) stated that copies of the relevant Research Report were now
available and would be circulated to the manufacturers. The Post Office
was not yet in a position to make a decision on Operator's Headsets. Col.
McMillan (GPO) said that it had been agreed earlier (Meeting 20) that the case should
be in two stages as follows:-
(i) Suggested general performance characteristics of operators sets
(ii) Detailed specifications of instrument parts to give the general performance
suggested in (i).
The Research Report was the Post Office contribution to stage (i). He
would like agreement that the specification should not be proceeded with until
the manufacturers' comments on stage (i) had been received. This was greed.
Mr Cameron (GPO) mentioned that as a result of a meeting between the P.O.
and the manufacturers' representatives it had been agreed that SCP 69 should be
reissued as a development SCP. This had now been done and the terms of
reference were those agreed at the meeting referred to.
10th January 1950
Mr. Combridge (GPO) said he had heard a suggestion that there should be a target
date of 3 months on this development. Mr. Smith (STC) replied that such a target
had been fixed voluntarily by the allocated Manufacturer. There was no
formal target date.
10th October 1951
Mr. Warren (GPO) said that some progress had been made since the last meeting
and a sample headset forwarded to the Department. The Chairman said this was
being examined. He inquired whether any action had been taken by the
Manufacturers on the suggestion to manufacture the American type headset. Mr.
Warren (GPO) replied that the matter was under discussion by the appropriate
16th January 1952
Mr. Combridge (GPO) said that the revised model had been seen and discussed. A
new model was in preparation.
17th April 1952
Mr. Combridge (GPO) said that the case was progressing on the lines
indicated in the L.O.s report. He passed around for inspection a
photograph of a dummy headset to the proposed design and mentioned that, whilst it had been
intended originally to utilize the "Mendresco" Hearing Aid receiver,
there a proposal now to use a smaller version of the rocking armature receiver
to give increased sensitivity.
16th July 1952
Mr. Warren (GPO) said that S.T.C. had completed the first samples which included
the modifications suggested by the P.O. Mr. Combridge (GPO) understood that a separate
acoustic model would be provided. Mr. Smith (STC) replied that it would be included
with the extra samples mentioned in the L.O.'s report.
15th October 1952
It was noted that the Post Office Liaison Officer (LO) was now Mr Spencer.
Mr. Warren (GPO) commented that the models suitable for transmission tests had
been provided to the Post Office. Mr. Helman (GPO) described the reactions of
female operators representatives to a proposed new headset and said the tendency
was towards conservatism. Representatives of the male operators were in
favour of a now headset, It might be that when actual models were put on trial
the female operators would change their views.
14th January 1953
The Chairman drew attention to a letter from the A.P.O. on the subject of
operators headsets which had been discussed at the last meeting of the B. T. T.
D.C. The A.P.O. had announced its intention of replacing all old to
headsets with items of modern design and early action was proposed. It was
stated that suitable sots of foreign manufacture were on the market and the
A.P.O. was faced with the choice of buying the foreign sets, developing sets
locally or awaiting completion of the SCP 69 development. The A.P.O. had
indicated willingness to await the U. K. development if this was likely to be
completed reasonably quickly. The Chairman said that S.T.C. had been made
aware of the A.P.O. intentions and had been consulted on the prospects of
samples of the SCP 69 headsets being available within six months. On the
assurance of S.T.C. a reply had been sent to the A.P.O. saying that samples of
the British sets would be available within six months. Mr. Smith (STC)
confirmed the position on the supply of models.
15th April 1953
Mr. Warren (GPO) said that 10 models had been sent to the P.O. Mr. Smith
(STC) inquired whether the further 10 were required. Mr. Williams (GPO)
replied in the affirmative. Replying to the Chairman, Mr Smith (STC) said that three samples had
been sent to the A.P.O.
15th July 1953
Mr. Combridge (GPO) said that the second ten models had been received. Six of
the models were in service at two exchanges and the trial of these was being
carried out with the concurrence of the appropriate staff association.
Discussions with the manufacturer on minor modifications were continuing.
14th October 1953
Mr. Combridge (GPO) said that the trial was proceeding, the operators' comments
had not yet been sought, but a number of breakages on the mouldings had occurred.
14th January 1954
Mr. Warren (GPO) said that S.T.C. were preparing further samples.
14th April 1954
Mr. Combridge (GPO) said the P.O. was anxious to go ahead with tests and asked
when transmitters and a model acoustic system would be available. Mr.
Smith (STC) replied that they would be ready quite soon. The Chairman remarked that
the A.P.O. as interested in this development and he imagined the matter might be
raised by the L.P.O. representative at the Main BTTDC meeting.
13th October 1945
Mr. Combridge (GPO) said that reports on the tests of the transmitters indicated
that they wore satisfactory and it was hoped to place an order soon.
12th January 1955
Mr. Combridge (GPO) said a further 500 telephones (250 black, 250 ivory) were
being ordered. Mr. Warren (GPO) confirmed that the specification had been
13th July 1955
Mr. Smith (STC) replying to the Chairman said he was hopeful that delivery would be
made in August, but he was unable to commit himself more definitely to a date.
12th October 1955
Mr. Combridge (GPO) reported that the field trial had begun a few days previously.
11th January 1956
The Chairman said he understood that the L.O.s had now been advised of some
comments received from operators taking part in the field trial. Replying to Mr.
Smith (STC), Mr. Combridge (GPO) said it was not known how long the field trial would last.
11th April 1956
Mr. Combridge (GPO) said the comments of users participating in the field trial were
expected shortly; he had heard complaints that the headbands were found insecure
on some heads. He hoped S.T.C. would be able to offer modifications.
11th July 1956
Mr. Paren (TAC) said that in view of the comments, S.T.C. would have new
samples for further trials available within a month. Mr. Combridge (GPO)
said there was severe pressure from users for new headbands. The P.O. was
however rather disturbed about frying - one sample had developed trouble within
a month, and he suggested that a joint meeting be held at Dollis Hill to discuss
ways and means of overcoming this. The Chairman added that confidence in
the design had been shaken and, in view of the time taken over, the development
so far, whether or not to continue with the design would have to be considered.
It was unfortunate that some publicity had been given to this headset because in
view of the seriousness of the frying the P.C. might, be forced to advise the
Administration and influential subscribers that there was a major technical
shortcoming in the design. He suggested that the Manufacturers should
exert all possible effort to overcome the difficulties. Mr. Paren (TAC)
said the suggestions would be followed up.
10th October 1956
Mr. Combridge (GPO), said a number of modified transmitters was now being tried
out. It was intended to order a 110 additional sets to put the transmitters in. Cords would be available in about a week.
Mr. Smith (STC) commented
that in the present standard position circuit the new transmitter was
9th January 1957
Mr. Combridge (GPO) said that there were indications that the modified
transmitters were developing trouble and further reports would be made. He
confirmed that the mechanically modified headsets were ready for testing.
Mr. Bryan (SES) reported that the cords which were required were only just being
10th April 1957
Mr. Troke (GPO) reported that tests had now been running for one month and there
had been no reports of frying to date. He had no information on the trials
reduced. feed current. A P.O. decision on the physical details of the
combined headsets was. still awaited.
10th July 1957
Mr. Troke (GPO) reported that the field trial of transmitters with reduced
feed current had continued for a further month, making four months in all, and
results were quite satisfactory. It was hoped to adopt the headset using a feed
current of 40 mA.
The P.O. had obtained some pre-aged carbon from ET and, with their
permission, had passed. it to S.T.C. to make up some capsules which had not yet
been tried out. Even if successful, this was unlikely to solve the
frying-troubles, as it was understood that E.T. were now experiencing difficulty
in obtaining this carbon and would be unable to supply further quantities.
Replying to Mr. Warren, Mr. Troke said that on main exchanges the only
modification to operators circuits would be a reduction of feed current to the
headset. He also informed Mr. Smith that S.T.C. would be safe to change
their tools to incorporate the changes in design made to date. The headset
was likely to be adopted by the end of the year.
Discussion followed on the quantities likely to be required and S.T.C.s
productive capacity. It was understood that P.O. requirements might be1000
per week by 1959. Mr. Smith (STC) said S.T.C, could meet requirements
provided that the quantities were not excessive. He was asked to give an
estimate at the next meeting of the quantities which could be produced over the
next two years.
6th October 1957
Mr. Troke (GPO) reported that the field trial of transmitters with feed
current limited to 40 milliamps had proved that this was satisfactory and would
be adopted by the Department wherever possible. The field trial with
pre-aged carbon has also now run a further month successfully. He wandered
whether the improved electrode washing technique would improve the performance
at feed-currents above 40 milliamps. Mr. Smith (STC) thought that this was
unlikely. Mr. Combridge hoped that satisfactory working at higher than 40
milliamps load would be possible, as a restriction to 40 milliamps might
in some applications be undesirable.
The Chairman stated that development of the Headset was now almost completed
and asked whether there would be difficulty in supplying in quantity. Mr.
Smith (STC) said the manufacturers could offer 50,000 headsets a year. The
Chairman noted this figure.
8th January 1958
Mr. Combridge (GPO) reported that the trials with pre-aged carbon and washed
electrode had now run for 25 and 20 weeks respectively without failure.
9th April 1958
Mr. Combridge (GPO) reported that checking of drawings was making good
progress and a meeting between the L.O.s had been arranged to discus points
arising. The Chairman commented that the P.O. was anxious to introduce the
headset into service from the technical standpoint, but a considerable sum of
money would be involved which gave rise to administrative and financial
9th July 1958
Mr. Warren (GPO) said that S.T.C. would send tracings of the P.O. acceptance
drawings to the P.O. shortly. Mr. Redington (GPO) commented that an order
was in process of being placed for 30,000 headsets. Authority had been given for
a programme of 60,000 spread over four years and the present order represented
two year's requirements compressed into 18 months.
8th October 19578
Mr. Combridge (GPO) reported that the headset specification had been agreed
and that the manufacturers comments on the receiver inset and transmitter inset
specifications were being studied. Mr. Warren (MSSC) inquired how the
resistor across the receiver was to be provided. Mr. Redington (GPO)
explained they were to be purchased and the receiver modified by the Factories
Department before fitting by P.O. staff: they were not for issue to the
manufacturers. Mr. Harding (GPO) mentioned that the resistors would be.
required only on some existing switchboards to reduce the excessive loudness.
(Note:- To assist manufacturers on export orders, the resistor will be shown
dotted on the assembly drawing - J.H.C.)
7th January 1959
Mr. Warren (MSSC) reported that the manufacturers comments on Specification
S508 had been sent to the Department. Draft copies of Specification S506 had
been received and agreed by the manufacturers. Proof prints of the P.O.
acceptance drawings had been received and were being considered by the
8th April 1959