Transistors for Sansui AU 717 power supply

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east electronics

east electronics

Member
Joined 2006
eastelectronics.gr
After a very quick look at the schematic i think that these transitors form a regulator to supply secondary circuits on the amplifier ...regulation is based arround a zener diode and the all circuit will be happily replaced and work by far better with a simple Lm317-337 circuit that will provide more clean power and 50 times more acurate than a simple tranistor and a zener diode

AU717 deserves a mod like that ... is one of the best amps sansui ever made together with a good restore and upgrade

on the other hand any NPN and PNP that is close or better specs will do the exact same job there since for this type of application transitor doesnt actually do anything serious

kind regards sakis

EDIT: from expirience i can tell you that transitors in such an application will almost never fail ...though electrolytics arround it may fail seriously and from wiring aspect you may have some short circuit that caused a transitor failure ( LM 317 337 feature short circuit and thermal proection built in )
check your issues carefully !!!
 
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embrown057

Member
Joined 2010
Most of all the orginal parts can be found either from B&D Enterprises or Audio Lab of Georgia. Be carfull the Audio lab of Georgia dose not send you subs like NTE or ECG they just are not up to the job. I also find it hard to belive all the devices are defective or are you just "shot gunning" the repair for age of the unit? Sakis is right on as far as the mods but keeping the circuit orginal is always my first attempt unless the design is junk and than it it realy worth it. I would look what the failure truly is and just replace the defective devices only. Brake out your IT-18 or whatever trans tester you have and check each device. Power supply problems are the simplest of all to troubleshoot and should not take much time. Let us know how your doing..
 
east electronics

east electronics

Member
Joined 2006
eastelectronics.gr
circuits like that provide actually no serius regulation .... after that if and for any reason there is a bit of load in any of the rails of te preamp will result one rail of 14 volts and one of 15.2 ....dont now how much will effect the sound but still doesnt look nice

Any way i will a agree that those will actually never fail in this circuit ...and also there is no actuall need to look fro subs ,,,any will do as long as is paired with the other ...

regards sakis
 
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jblmar

Member
Joined 2005
No, not shot gunning. The owner of the amp wants to replace the parts. I'm sure that the problem is the zener diode, transistor or defective cap.
Can't go wrong replacing the circuit. It's only a few parts.
The circuit from the power supply to the right channel of the preamp is the problem.
 
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