This has a multi-pin socket for each cassette and provides all the inter-
cassette signal connections. It has two spade terminals on flying leads for
connecting the circuit earth chassis to a terminal on the frame.
9.4.2 Power Cableform
This has a 6-pin socket of which only two pins are used for supplying 50V
a.c. to the cassette Power Units, the centre tap of this supply being earthed at the
Main Power Unit. The plugs on the cassette Power Units to which these sockets
are applied have +20, 0 and –20V on pins 3, 4 and 5 respectively for test purposes.
In order to minimise the risk of hum injection into the signal cableform from the
power cableform, the latter employs twisted screened cable, the screen of which is
also earthed at the Main Power Unit. A power supply cable extension lead using an
11-pin plug and socket is used to connect the power cableform to the Main Power
Unit.
10.
MAIN POWER UNIT
10.1 Function
This accepts mains supplies 204V to 252V, 45 to 65Hz. It contains an a.c.
stabiliser and a step-down transformer to provide the 50V, centre tap earthed supply
for the Cassette Power Units. It also contains cue Output Amplifiers and their
Power Units, condenser microphone power units, relays to operate the buzzer and
red light, relay power supply and metering.
10.2 A.C. Constant Voltage Regulator
This uses a solid state control circuit. It is set for 240V out and for an input
range of –15%, +5%, i.e. from 204V to 252V. If desired this can be altered to
±
10%,
i.e. from 216V to 264V. The ranges are selectable by changing the connections to
both the input range terminals.
The following are its other main features:
Output current
1.5 amps max
Output accuracy
±
0.3% r.m.s., zero to full load
Time constant
0.1 sec.
Frequency range
45 to 65Hz.
Distortion
Total harmonics less than 3.5% at
unity power factor. Slightly greater
at other power factors.
Environment
Rated for use up to 45
°
C Ambient
temperature.
