Kenwood TS-60S Service Manual page 12

50mhz all mode

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CIRCUIT DESCRIPTION

ALC

circuit

The forward wave voltage detected in the filter unit

passes through CN18 in the TX-RX unit, its level is ad-

justed by VR14, and it is applied to the differential

amplifier comprising Q1 and Q2 (2SC2712(Y) x 2) in

IC11. When VSF is applied to the base of Q1, the

emitter voltage of 0 1 and Q2 increases and the current

flowing through the base of 0 2 decreases; thus the

collector voltage rises. When this voltage exceeds the

emitter voltage of Q3 (2SC2712iY)) (about 1.8V) plus

VBE (about 0.6V), the current flows through the base

of 0 3 and the collector voltage drops. ALC time con-

stants

and R are connected to this collector.

The collector voltage change is shifted by Q4

(2SK208) and D2 (3.6V), and matched with the voltage

for keying by 0 5 and D3 (RLS73) to generate the ALC

voltage. This ALC voltage activates ALC by lowering

the second gate voltage of Q43 (3SK131(M)) of theTX-

RX unit. (Fig. 11)

2. Power control circuit

Power is controlled by lowering the base voltage of

0 2 in IC11. As the base voltage of Q2 decreases, the

emitter voltage of 0 1 and Q2 decreases. This acti-

vates ALC and reduces the power even if the base

voltage (VSF) of 0 1 is low. The power is changed by

IC12. In AM mode. 0 6 3 turns on, and the power is

reduced to about 114 of the power in other modes.

(Fig. 11)

VSF

Fig.

11 ALC and power control circuits