SA 5063/1 →
← SA 5031
Telephone set used with scrambler phone
Introduced in early 1943 for use on LB
(CBS 2 & 3) and
Magneto systems, and on for use on long lines with
It consists of a Tele. No. 394 with a Key No. 303A switch assembly,
a 12-wire line cord ending in a BT No.6 1 connection box,
and a No. 164 Jade Green handset .
The SA5063/0 was either used on a direct exchange or
PBX line, or with the
SA5050 Unit Auxiliary device to allow
up to three SA5063/0 sets to share a single Frequency Changer unit.
The SA5063/0 has two push-buttons, labelled
SECRET and ENGAGE FOR SECRET 2
but the latter (ENGANGE FOR SECRET) has no function if the
set was connected to a direct exchange line. A third
button could be added to release the other two
without placing the handset in the cradle, or for use with various
extension plans. In such cases the label was changed accordingly.
The image above shows a typical SA 5063/0 that is
(barely readable) marked as such at the bottom.
It also carries the
manufacturing code FBA/1, which suggests that it was made at
the GPO factory in Birmingham (FB). It is built on a 396 chassis
and has a black 164 handset that is (partly) painted lime green.
In this case, the bakelite body has no provisions for a third button.
The majority of SA5063 (SA5063/0) units were factory
assembled, but they were also occasionally built by engineers
in the field from locally available parts. For this reason it
is possible that some units are marked Tele. No. 394 on their
base and chassis.
Due to wartime shortages, the chassis
of the Tele. No. 396 was sometimes used as a replacement,
as illustrated by the object above.
20-way box with metal lid.
Later: SCRAMBLE and HOLD SCRAMBLER.
A scrambler system like the Frequency Changer, does not provide any
real protection against a professional eavesdropper. All the intercepting
party has to do, is reverse the speech spectrum once more to make the
conversation intelligible again. This was known by the UK's War Office,
but it was believed to be sufficiently secure against a casual eavesdropper,
such as the operator in a manually switched exchange, or a service
engineer working on the telephones lines.
In order to discriminate scrambled telephone lines from regular
ones, circular labels were issued to mark a regular phone as insecure:
SPEECH ON TELEPHONES IS
These labels were fitted in the area around the dial or the blanking
panel. Although they were intended for regular phones, they sometimes
landed on scrambled phones as well. On the majority of scrambler phones
it was omitted however. The label on the phone in the image on the right
is therefore considered out of place.
Note that many 'scrambler phones' that are offered on auction sides
such as eBay, carry a circular label that is clearly a (bad) reproduction
of the original one. In many cases, a simple typeface like
'Helvetica' or 'Univers'
is used, whereas the original one was typeset in 'Gill-Sans'. If you
insist on having this label installed on your telephone, you may want to
download this reproduction [A].
With the exception of the very early Frequency Changers – that were
equipped with a No. 162 — nearly
all wartime installations used a voice terminal that was based
on the chassis of Telephone No. 394 or 396, both members of
of GPO telephones that started life in 1937.
In all cases, the telephones were given a green handset, so that
the voice terminals
used with the Frequency Changers (scramblers) could
be distinguised from regular (unprotected) telephones.
The Jade Green version of bakelite handset No. 164
was used for this. The one at the right in the image above is of this
type. The same one was used with the earlier
Telephone No. 162.
In this case the receiver 1 has a black cap rather
than a green one, for which there was a good reason.
Standard 164 handsets were fitted with a receiver 2 that was considered
of insufficient quality for use with the scrambler system.
An engineering directive was therefore given that these should be
swapped for alternative ones, 3 but these were only
available in black bakelite for most of the war period.
A 164 handset with a black receiver cap can also be spotted in the
photograph of the Cabinet War Rooms
at the top of this page, in which it is held by
Royal Navy Captain Richard Pim.
When green handsets were is short supply during the war, regular
black 164 handsets (or sometimes ivory as well)
were painted in a lime green colour that did
not match the colour of the Jade Green handsets. The leftmost
example in the image above is of this type. The braided cord of
the handset could be green or brown, whichever was available.
Also known as earpiece or speaker.
By default, Receiver No. 1L, Diaphragm No. 12, and Receiver
Cap No. 18 were installed on handset 164.
The replacement consisted of Receiver No. 2P,
Diaphragm No. 25 and Receiver Cap No. 23.
There are also different variants of the metal shield with the text
labels that is mounted just below the SECURE and CLEAR buttons. At least four
version have been spotted over the years, which are shown below. In all
cases, the leftmost button is used to go secure (secret, scramble),
whilst the rightmost button is used for clear speech
(normal, hold scrambler, engage for secret).
We believe the above label to be the eldest as it does not appear
in the 1952 list of labels that was used at the GPO.
Furthermore it is present on the phones in our collection that were
made in 1938 and 1940 respectively.
Other labels that are known to have been issued over the years are:
Depending on the configuration of the telephone set, the user requirements
and the presence or absence of a third button at the centre,
other arrangements and text labels may have existed. The labels could be
engraved or screen printed.
If it was screen printed, a condensed variant of the Gill-Sans typeface
was commonly used.
For a complete overview of the 27 different
text labels No. 252 & 253 that were available between 1952 and 1967,
please refer to list N620
➤ Overview of text labels
Although it was technically possible to fit a dial to a 394/396
telephone body, the standard issue was without one, as most installations
were used on manually switched networks during WWII. In that case the
circular hole at the front of the telephone set was covered
with Blanking Panel No. 3.
Furthermore, the British Government had its own private network
– completely separated from the public switched network – and
many of its users, including Churchill, relied on an assistent
to set up a call via the exchange operator and initiate
a conversation, before handing it over to the user.
If the scrambler was used on networks with automatic exchanges,
or on a local PABX that had automatic exchange facilities,
the voice terminal could be fitted with a dial, so that
the user could select the extension number directly.
This is the case with the SA-5030 shown here.
In post-war systems, most voice terminals did have
a dial, as automatic exchanges had meanwhile become mainstream
in most countries. Nevertheless, the blind telephones sets (i.e. units
without a dial) remained in use in many installations, in which case
the line terminals of the Frequency Changer were commonly connected
in parallel to a regular telephone set (with dial).
➤ More about the SA-5030 with dial
The voice terminals shown on this page are authentic and were
used with a Frequency Changer during WWII. According to the stamps,
one was made in 1938, whilst the other one is of 1940 vintage.
The green handset was made in 1935. The painted one in 1940. The bottom
panels are marked SA 5063/0
and SA 5063/1,
which means they were issued in 1943 and 1944 respectively.
The problem with these two sets however, was that a previous owner had
converted them into house telephones, or intercoms, and used them this way
for several years. Obviously he wanted to avoid the use of a small exchange,
or PABX, and had converted them for low power use.
The original bell had been removed and its space was used to
accomodate two 4.5V batteries:
one for the speech loop and one for a small buzzer
that was mounted to the chassis. Luckily, the previous owner had applied
his modifications in such a way that they could easily be reversed.
A bakelite button had been added to the center
of the circular panel that covers the hole of the dial,
but this too was easily removed.
The bad news was that the batteries were left inside the phones when they
were taken out of service. Over the years, the leakage from the batteries
had caused considerable damage
to the bottom panel and to the small drawer at the phone's front.
Restoration of the phones was started by first taking them fully apart
and cleaning the indiviual parts. The modifications were removed and undone
and the bakelite body
of the unit was washed and treated with bakelite conditioner. 1
The missing parts were then re-mounted to the chassis and the
original wiring was restored as per circuit diagram inside the bottom panel.
The braided cord of the green bakelite handset was replaced with a
high-quality reproduction 2 and a new braided line cord was added to allow
it to to be connected to a standard telephone line.
Both phones are now fully restored to their original state
as close as possible. The only thing missing right now are two original
Frequency Changers to connect them to, so that we can finally demonstrate
how Churchill and his staff held private phone conversations during the war.
High-grade bakelite conditioner and other products for restoring
bakelite parts are available from a variety of sources,
such as this one.
High-quality reproduction cables for old GPO phones, that closely
match the original colours and manufacturing properties, are
available from Chris Elliot in the UK.
Any links shown in red are currently unavailable.
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© Crypto Museum. Created: Wednesday 26 May 2021. Last changed: Monday, 07 June 2021 - 07:34 CET.