KR4200 is a Stereo Am/Fm Tuner with an Internal Amplifier built in by KENWOOD in the 70s that delivers up to 19 watts of audio per channel at 8 Ohm loads.
The Power Section includes an amplifier with a small power which is the owner could enjoy this audio in a room that is not too big.
SCHEMATIC DIAGRAM
The following is a re-drawn schematic from the original one cause not so clear/blurred schematic.
This circuit schematic is quite simple because it uses not so many components.
Pay attention, then this series is in line with the legendary 150 Watt OCL in Indonesia. Although there are many components that are not the same as OCL.
The components for the preamp are use transistor number C1345.
An estimated audio gain is 100 X based on the value of the feedback resistor R6 to the input resistor R5.
Transistor Q3 acts as a voltage amplifier coming from the collector of Q1. C4 acts as an AC Bypass capacitor to get a larger gain value.
There is no servo driver in this circuit, it’s just that it relies on the thermistor and trimpot for IDLE.
Q4 and Q5 serve as amplifier drivers that amplify the output current from Q3 and from the base of Q5.
Finally, the power transistor uses the number 2SD335 paired with the transistor number 2SA626.
The supporting component of D3 with a value of STV-3 is a diode which contains 3 forward-directed diodes whose job is to rectify the current .
Transistor Power uses a pair of numbers 2SD335 and 2SA626 which according to the datasheets it has an output capability of up to 100 Watts.