The R376 is an Am/FM radio receivers and stereo amplifiers made by HH SCOTT which were produced in the 70s.
It produces an audio output of 75 Watts per channel at 8 Ohm load.
The amp has used amplifier technology with class G, which uses double voltage for the purpose of increasing amplifier efficiency.
INFO
Inside of R376 receiver just looks like below:
SCHEMATIC DIAGRAM
The result of edited and cropped schematic diagram looks like this:
Q707 and Q708 are driver transistors and Q709, Q710, Q711, Q712 are the output transistors.
CLASS G AMPLIFIER
When the input signal levels are low, the smaller power transistors, Q711 and Q712, operate to drive the speaker from the supply voltage at B (L).
When the input signal level exceeds a predetermined level, Q709 and Q710 will start to conduct an addition to Q711 and Q712.
With the higher input signal, the emitter voltage of Q711 and Q712 exceed +B(L) and -B(L). The output current drawn from +B(H) and -B(H).
The function of diodes CR705-708 and CR709&710 are to eliminate distortion caused by current limiting. The actual number of diodes will vary depending on VCE ( sat ) of Q711 and Q712.
Also diodes CR703 and CR704 are for prevent from destroying transistor Q707 and Q708 from excessive VBE.
Diodes CR711 and CR712 are to prevent excessive VBE from destroying Q709 and Q710.
Resistors, R719 and R720 , and Capacitors C710, C709 are working for minimize distortion at high frequencies.
TRANSISTOR PROTECTION
This circuit protects the output transistors from damage by limiting excessive collector current if, Ic +Vce should exceed specified rating.
For example, R725 is sensing the excessive collector current in Q709 and Q711 . Furthermore, Vce is divided by R713, R717 and R715 and is added between B and E of Q705.
When the base-emitter voltage exceeds 0,6V, Q705 turns on to control the current flowing through Q709 and Q711.
NOTE
D586 = 60 Watts ( datasheets )
D581 = 60 watts ( datasheets )
B611 = 60 watts ( datasheets )
B616 = 60 watts ( datasheets )
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