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Sencore SG165 Power Supply Question - any experts?

Markus111

Big Horns & Many Tubes
Subscriber
I picked up an SG165 a little while ago, and I've been having a lot of fun restoring it. I changed all of the electrolytics, and have been able to go through the calibration procedure and get some decent results. One thing continues to bug me though. The voltages from the power supply are +12.5v and -12.5v, which is half a volt higher on each rail than it should be. From what I've been reading, this could affect the life of some of the transistors, as they are operating right at borderline.

So my question is: How might I modify this power supply to get it down to +/- 12volts or slightly less? In one of the posts I read, someone was able to modify the PS to put out +/- 11.5v. Of course now I can't find the post. Any help would be appreciated!

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Lowering value of r110 will reduce both + and - supplies. When yu get the + value dialed in, the variable resistor should adjust the - voltage. start witg 5.1k or 4.7 k for r110 (or another pot)
Also, check the voltage drop across the zener - this is the reference for the rest of the regulator circuit.
 
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