After troubleshooting using ” freeze spray ” for transistors method found 2 transistors 2SA726 in right channel driver board acting bad after cold application . All unit transistors 2SA726 changed to 2SA992 . They have same look but different pinout. Pay attention ! 2SA992 / KSA992 is better in parameters and performance.
After troubleshooting found missing voltage on collector H702 transistor ( 4-5 volt) in driver section.
Problem solved by replacing R708 resistor 18k.
This time we did ” lazy” replacement . New 2 resistors 10k + 8k installed right on top of bad resistor. For saving time.
Nice small amplifier. Good performance. Nothing special.Power supply section extremely simplified. Classical old style engineering design.
Problem solved by OUTPUT PLUG REPLACEMENT.
Technical design review.
Pluses- simplicity, build simple as possible. Minimum wires used in design . Servo loop channel method ( input signal controlled by output signal) realized in schematic. This method has own advantages and minuses. Some called it “over kill” and unnecessary, some – perfect and high performance support method. Elimination input electrolytic capacitor in signal path is questionable. Debates in process already for over 30 years. Still unique .
Low power unit use for functioning. Good detailed attention to phono input section.
Minuses- no ventilation holes, using no soldering contacts on major transistors ( oxidation )
Power supply filter capacitors installed close to heat emitting heat sink ( heat destroy electrolytic ), not shielded balance pot wires.