|
|
|
|
|
|
General information
This page contains some general information about the 300-series
GPO telephones, in particular information about the 394 and 396
models that were used as part of the
Secraphone (scrambler phone).
For more detailed information, please check out the links at the bottom
of this page.
The GPO 300 series was developed in co-operation with Ericsson UK
and is based on the Ericsson N1015, N1016, N1017, N1374 and N1376
models [4], albeit with a British GPO No. 164 handset.
|
|
A few examples of phones in the 300-series:
|
332 Basic unit with dial, bell and handset (no buttons)
330 Version for private branch exchange (recall button) 1
312 Version for Shared Service installations (party line)
332 CB Version without dial (and sometimes without drawer)
394 LB 2 or 3-button version for CB systems
396 LB 2 or 3-button version for CBS systems
|
-
The recall button connects earth (ground) to the telephone loop.
|
The drawing below shows the standard terminal block that is present on
all 300-series GPO phones. It is mounted at the bottom of the metal chassis
and is normally used for connection of the line and the handset. All components
of the telephone, such as the transformer, the bell, the capacitor, the dial
and the hook switch are connected to this terminal block.
Note that on Secraphone voice terminals,
additional wiring is present via the 9K terminal block.
Pinout is as follows:
|
| |
Connection block T as seen from the bottom of the phone
|
For a standard telephone set, the line is usually connected at 1 (A) and 9 (B),
and the handset is connected at 4 (M), 5 (MR) and 6 (R). There should be
shorting strips between 1 and 2, between 8 and 9 and between 10, 11 and 12,
as indicated by the red lines in the drawing above. If you want to convert
a telephone set for use on 'modern' analogue systems, check out
this website.
➤ How to convert a telephone for use on modern networks (off-site)
|
|
|
|
|
|
|
The 394/396 telephone, that is used as the voice terminal of the
Scrambler,
has two or three switches at the top of the bakelite case.
These buttons directly operate the
303A key unit
(also known as a 9K
switch pack) which consists of two 4-pole make-before-break switches (4K)
and one single-pole
make-before-break switch (1K) mounted in between the other two.
For other types of key units, check out
Robert Freshwater's excellent website
[3]. The pin-out of the 9K:
|
| |
Connection block 9K as seen from the rear of the phone
|
Each of the contacts of this terminal block, with the exception of
contact 28, is wired to one of the contacts of the 9 individual switches.
Contact 28 is not connected (nc).
When looking from the front of the telephone, the three buttons are identified
(from left to right) as A, B and C. Pressing a button, automatically releases
the other buttons. Depending on the configuration, the keys are latching or
momentarily. In our case, only the rightmost button (C) latches when it is
pressed. On some phones, the buttons are also released when the handset is
placed in the cradle (on-hook).
|
| |
The switches inside the 9K switch pack with their terminal numbers
|
Note that the individual switches of the 9K switch pack, are of the so-called
make-before-break (MBB) type. This means that when pressing the button, there
is a short moment when all three contacts of the switch are connected together
(shorted). This is the opposite of the more common
break-before-make (BBM) switch.
Although standard switch symbols are used in the diagram above,
make-before-break (MBB) switches are sometimes explained with the
following symbols:
|
| |
Three possible symbols for MBB switches.
|
The individual contacts of each switch are usually named as in the diagram
above. The fixed contact, or mother contact, is known as common (c).
The contact that is connected to the common when the switch is in rest, is
known as the normally closed contact (nc). The contact that is connected to
the common when the button is depressed, is known as normally open (no).
The behaviour of the push-buttons can be 'programmed' with a control plate
that is fitted behind the spring-loaded
latching bracket at the front
of the 303 key assembly. It can be installed in four different orientations
with two positions each, giving a total of
eight combinations as shown here:
For clarity, the notched control plate is shown in red. The presence of
a notch prevents the button from being latched. If there is no notch,
the button will be latched when it is pressed, whilst releasing the other
buttons. A good suggestion for use in the scrambler phone, is setting (2).
|
|
Some telephone sets, in particular the SA5063/1 1 that was used as the voice
terminal of the Scrambler Phone
from 1944 onwards, were fitted with a
No. 330B key unit.
Built from the same parts,
it is very similar to the 330A, but lacks the facilities for
the centre button.
|
|
Below is a non-exhaustive list of manufacturer codes found on an inside
GPO/BT telephones. The list is by no means complete or correct, but might
be of use when restoring old telephones.
For a more complete overview and additional information, please refer
to this website
[1].
|
|
A
|
|
Edison Swan Electric Ltd.
|
|
AA
|
|
Pinching & Walton
|
|
AAG
|
|
Mullards Ltd
London
|
|
AAR
|
|
Associated Automation
|
|
AEG
|
|
GEC Telecommunication
Glenross (Scotland, UK) [not to be confused with the German AEG]
|
|
AEI
|
|
Associated Electrical Industries
Later: Henley Cables.
Henley later took over Siemens Bros and Thorn EMI and was then taken
over itself by GEC Telephones.
|
|
AEK
|
|
GEC-AEI Telecommunications
Kirkaldy (Scotland, UK)
|
|
AK
|
|
Peel Conner
This was the telephone manufacturing branch of GEC UK from 1910 to 1921.
Later markings include GEC and AKE.
|
|
ATL
|
|
Austin Taylor Ltd
Bangor (Whales, UK)
|
|
C
|
|
GEC
Coventry (UK). Currently known as GPT.
|
|
DAE
|
|
A.P. Besson Ltd
Hove (Sussex, UK)
|
|
DFM
|
|
Denis Ferranti Meters Ltd
Bangor (Gwynedd, UK)
|
|
E
|
|
British Ericsson
Later: Plessey, later: GPT
|
|
ET
|
|
British Ericsson
Later: Plessey, later: GPT
|
|
EET
|
|
Plessey
Beeston (Nothinghamshire, UK)
|
|
EEX
|
|
Plessey
Sunderland (UK), formerly Ericsson
|
|
FB
|
|
Post Office factory
Birmingham (UK)
|
|
FBR
|
|
Post Office factory
Birmingham (UK) Refurbished items
|
|
FED
|
|
LM Ericsson
Sweden
|
|
FH
|
|
GPO Factory
Holloway (UK)
|
|
FHB
|
|
Factory Holloway (Construction)
|
|
FHR
|
|
Post Office factory
Holloway (UK) Refurbished items
|
|
FNR
|
|
Post Office factory
Edinburg (Scotland, UK) Refurbished items
|
|
FWG
|
|
STC Consumer Electronics
Cwmcam (Wales, UK)
|
|
FWR
|
|
Post Office factory,
Cwmcam (Wales, UK) Refurbished items
|
|
GEC
|
|
GEC, Coventry (UK)
Currently known as GPT
|
|
GEN
|
|
GEC-AEI Telecommunications
Newton Aycliffe, Co. Durham
|
|
GNA
|
|
PYE
Aidre (UK). Later renamed TMC.
|
|
GTE
|
|
Dennis Ferranti
Ferranti imported or licensed GTE phones, as part of a joint venture
with GTE USA and GTE Belgium.
|
|
H
|
|
Automatic Tlephone and Electric (ATE)
Later marked as PL (Plessey)
|
|
HAA
|
|
Plessey Strowger Works
Liverpool (UK)
|
|
KRM
|
|
Krone
Cheltenham (UK)
|
|
PEH
|
|
Pye
Hastings
|
|
PL
|
|
Plessey
Later became GEC-Plessey Telephones (GPT).
Many of the war-time 300-series telephones were manufactuered
by Plessey and will therefore have the PL marking.
|
|
PX
|
|
Phoenix
Hendon, London (UK). Later PXA.
|
|
PXA
|
|
Phoenix
Hendon, London (UK)
|
|
S
|
|
Siemens Brothers
Later AEI, later: GEC, now: GPT.
|
|
SB
|
|
S.G. Brown Ltd.
|
|
SEA
|
|
Siemens-Edison Swan
London N17 (UK). Later part of AEI.
|
|
SEG
|
|
AEI Ltd
Woolwich, London SE18 (UK).
Formerly Siemens Brothers (S).
|
|
SER
|
|
AEI Ltd
West Hartlepool, Co. Durham (UK).
Formerly Siemens Brothers (S).
|
|
SEW
|
|
Siemens Edison Swan
Woolwich, London SE15 (see also SEA).
|
|
SPK
|
|
Plessey
Speeke, Liverpool (UK)
|
|
STC
|
|
Standard Telephone Company
New Southgate, London (UK)
|
|
STM
|
|
Standard Telephone Company
Belfast (Northern Ireland)
|
|
TE
|
|
Telephone Manufacturing Company (TMC)
|
|
TEA
|
|
Telephone Manufacturing Company (TMC)
West Dulwich (UK)
|
|
TES
|
|
Telephone Manufacturing Company (TMC)
St. Mary (UK)
|
|
TGR
|
|
Thorn-Ericsson
Rochester (UK)
|
|
TGW
|
|
Thorn-Ericsson
Scunthorpe (UK)
|
|
TMA
|
|
Telephone Manufacturing Company (TMC)
Airdrie (UK)
|
|
W
|
|
Western Electric
Later: STC.
|
During WWII, most 300-series telephones were manufactured by Plessy and by
TMC (also Pye-TMC), especially the ones that were used for the war effort.
This means that the most likely codes to be found on these devices are
PL, TE, TEA, TES, TMA and GNA.
|
High-quality reproduction parts, such as braided handset cord and line
cords, that closely match the original colours and production processes,
are available from
Chris Elliot, Vintage Telephone,
in the UK [5].
Some fully restored GPO telephones are available here as well.
➤ Visit website
|
|
Expressions and abbreviations used on this page:
|
|
BT
|
|
British Telecom
Arguably the largest telecom operator of the UK. Previously state-owned
and known as the General Post Office (GPO).
|
|
CB
|
|
Central Battery system
System in which all the energy needed for transmission and signalling
is delivered by the exchange. No local batteries or hand generators are
used at the telephone end.
(More [3])
|
|
CBS
|
|
Central Battery Signalling system
Similar to a CB system, except that the mircophone is powered locally
by a battery at the telephone end. Power for signalling is provided by the
exchange as in a CB system. In the UK there were three types of CBS.
(More [3])
|
|
GPO
|
|
General Post Office
The state-owned post and telecommunications operator in the UK, before it
was renamed BT and privitised. The GPO was als known as British Post
Office (BPO) and simply as Post Office (PO).
It is currently known as British Telecom (BT).
|
|
PL
|
|
Plessey
Manufacturing code used on the body of the telephone sets and also
inside, often stamped on the chassis. The manufacturer's code is also
cast inside the bakelite body.
|
|
TE
|
|
TMC (see below)
Manufacturing code used on the body of the telephone sets and also
inside, often stamped on the chassis. The manufacturer's code is also
cast inside the bakelite body.
|
|
TMC
|
|
Telephone Manufacturing Company
The original manufacturer of the Secraphone in St. mary Cray (Kent, UK) [6].
|
- Handset No. 164 circuit diagram
First released 25 January 1935. Issue C, 5 January 1968. 1
- Telephone No. 332 circuit diagram N-432
First released 3 October 1951, Issue E, 22 February 1968. 1
- Telephone No. 394 circuit diagram
First released 30 September 1937. Issue A, 25 January 1968. 1
- Telephone No. 396 circuit diagram
First issued 16 July 1937. Issue F, 26 January 1968. 1
|
-
Documentation obtained from Robert Freshwater [2].
|
|
|
|
Any links shown in red are currently unavailable.
If you like the information on this website, why not make a donation?
© Crypto Museum. Created: Tuesday 28 January 2014. Last changed: Friday, 07 September 2018 - 10:04 CET.
|
 |
|
|
|
