Continental Electronics 816R - Page 14

PLATE ON circuitry. The supply is protected
through circuit breaker A6CB3.
Power Control Unit, A9.
Power control unit A9 regulates the 3-phase ac
power input to the power amplifier plate and the
power amplifier screen transformer. SCR assembly
A9Z1 has three SCR pairs; one pair in series with
each primary winding of the 3-phase power
transformers. Each pair is connected within the
delta circuit of the transformer primaries. Three
control cards are located within the A2 card cage.
Each control card controls the firing (tum-on) point
of one SCR pair (Refer to Figures 7).
A common de control signal from power control
regulator A2A6 is fed simultaneously to each
control card. This control signal governs the firing
of the SCR pairs that regulate the input power
applied to the power supplies. Upon receipt of a
PLATE OFF control signal, a ground is placed
across the inputs of each card.
Power Control Regulator, P/O A2A6.
The power control regulator located on A2A6
provides the necessary control signals to operate
power SCR control unit A9. Assembly A2A6
supplies a soft-start power amplifier plate supply
tum-on signal, a negative voltage for manual power
control, and amplifier mixer functions for
automatic power control.
When the PLATE ON switch is pressed, 28 V de is
supplied to A2A6J1-32. The 28 V de activates
transistor QI to turn on relay A8K6. Relay A8K6
in turn supplies 3-phase ac control power to
A2Tl,2,and 3. An RC time delay circuit formed by
resistor A2A6R41 and capacitor A2A6C12
maintains A8K6 closed for a short interval after the
PLATE OFF switch is pressed. Transistors Q2,
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