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Modulator. Two 5-500A pentodes are operated Class AB, push-pull, to supply a modulating signal to the PA.

Transfor mer coupling provides correct impedance matching, while a reactor is employed in series with the piąte supply to provide a path for the dc PA piąte current.

This transformer is a special Iow distortion design. At transmitter power cutback, the modulator piąte voltage is reduced simultaneously with the PA piąte voltage. The modulator screens are coupled together through stabilizing resistors to the screen supply. Rf bypassing is used to prevent high frequency oscillations. Modulation capability of 125% on positive peaks is assured, allowing high average modulation with a minimum of distortion. Use of the 5-500A pentodes lengthens tubę life and reduces operating costs.

820D-2 PA Compartment

Metering Circuits. Individual meters are provided for mea-

suring PA piąte voltage and PA piąte current. Accuracy of    ■ ■

measurement is within 2% of fuli scalę. An eight position

multimeter is also provided to meter additional parameters,

including screen voltage, PA grid current, bias vollage, rf

driver collector current, 28-Vdc supply voltage, screen

current, modulator cathode current, and the 290 V supply

voltage.

Power Supplies. 28 Vdc Supply: The 28 Vdc supply pro-vides power to the control circuits, pilot lamps, and rf and audio drivers. Power to the supply is routed via the Iow voltage Circuit breaker through a protective fuse to the transformer primary. A fuli wave bridge is used for rectification, while the output is filtered and regulated to

reduce ripple.    8200 2 Lower Compartment

AUCNO

INPUT

1*0 *00 OHMł 10 OIM t 2 OB

820D-2 Błock Dogram

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