SWITCHBOARD SA 8120
|P.O. ENGINEERING DEPT
Issue 1, Oct 1950
“SWITCHBOARD, P.A.B.X., SA 8120”
The switchboard consists of a wooden case with a sloping front panel, cast in aluminium alloy, and a detachable baseboard. Equipment is arranged within the switchboard case as described below:-
(a) The baseboard is fitted with two “Jacks No. 40’ to which the cable from the automatic unit is connected, see par. 10.
(b) The cabinet is provided with two ‘Plugs No. 3201’, which fit into the ‘Jacks No. 40’, so that it is possible to remove the cabinet without disturbing the permanent wiring.
(c) The face equipment accommodates the keys detailed below:-
2. Use of Position Keys
(a) Dial. For connecting the dial to the exchange, to automatic inter-switchboard circuits and manual extensions.
(b) Ring. For ringing on '0’ level circuits and generator-signalling private circuits.
(c) Interrupt. This enables the P.A.B.X. operator to offer a trunk call to an engaged extension. (A ticking noise is superimposed on the extension circuit, when the operator enters the connexion, to warn the extension that the operator is in circuit.)
(d) Flash and cancel. This enables the operator to call-in the public exchange operator on an established call, or to release the connexion after a dialling error.
(e) Splitting i.e. Speak-extension, Speak-exchange. This enables the operator to speak on either the extension or public exchange side of the connexion.
(f) Engaged Test. This enables the operator readily to ascertain free lines. Operation of the key causes a steady glow on the calling/supervisory lamp associated with any exchange and inter-switchboard circuit while the circuit is in use, see par. k.
(g) Release. This enables the operator to release an exchange line which has not been keyed to an extension number.
(h) Alarm Cut-off. This is used to disconnect the alarm signal in the case of a P.C. or other alarm.
(j) Audible Alarm. When this key is in the operated position, an audible alarm is given on every calling signal.
(k.) Night Service. This is operated when the operator vacates the switchboard. The operation of the key arranges for calls incoming on exchange and inter-switchboard circuits to be answered by selected extensions, who dial “8” to gain access to the calling line. This key is of a special locking type to prevent accidental restoration when cleaning or dusting the switchboard.
3. Digit Key Strip
4. Calling and Supervisory Lamps
(a) A flicker signal on a lamp at a frequency of 0.2 sec. on: 0.2 sec. off - indicates a calling circuit.
(b) A steady glow on a lamp (i.e. during the setting-up of a connexion on the switchboard, but see par. 9) indicates a free extension. This glow ceases, however, when the extension answers.
(c) A lamp flashing at 0.75 sec. on: 0.75 sec. off indicates an extension busy.
(d) The appropriate supervisory lamps glow steadily when the ENGAGED TEST key is operated, to ascertain a free exchange line or inter-switchboard circuit.
5. Alarm Lamps
(a) P.G. Pilot. This is fitted with a white opal and, when glowing, indicates a permanent loop due either to a faulty line, a misplaced handset or a handset not replaced after a call.
(b) Auto Alarm. This is fitted with a red opal and, when glowing, indicates an alarm-type fuse blown or a switch failing to release.
(c) Mains Fail. This is fitted with a red opal and, when glowing, indicates failure of the mains supply.
8. Rear Equipment
An incoming call is indicated by a flicker signal on the appropriate lamp. To answer, the SPEAK key lever is moved towards the lamp; the lamp will continue to flicker. Ascertain the extension number required, and key-up on the digit-key strip. If the extension line is free, the flicker signal on the lamp will change to a steady glow indicating the extension bell is being rung. The SPEAK key may now be restored to normal and when the extension answers, the lamp will cease to glow.
At the conclusion of the call, the connexion will be cleared automatically. No further action on the part of the operator is, therefore, necessary.
If the extension keyed is busy, the flicker signal on the lamp will change to a busy flash of the calling subscriber is prepared to wait, the SPEAK key may be restored to normal, and the lamp will then continue to flash until the extension becomes free. The caller is then connected automatically to the extension without further intervention by the operator.
Superseded by Switchboard SA8133.
Switchboard front view
Switchboard with front cover open
Rear view of Switchboard with back cover opened
Last revised: April 10, 2019