Arrgh linear series supply ripple - how come my zener is rippling?

[vibroverbus]

I'm trying to fix up a slightly noisy PS in an old Akai Tuner and can't seem to get the ripple out.

Design is bone simple linear series like out of an old textbook - one BJT and one zener with current limiting resistors and what I would think should be plenty of filtering.

Getting 30ma of AC ripple, and it appears on the output of the zener so duh the BJT happily puts it right back on the output.

Have replaced just about everything in the circuit except the 2 resistors.

Here's the schem as well as a pic of the ripple I'm getting.
I am an idiot I know I'm missing something obvious. Help for this idiot would be greatly appreciated.

Thanks in advance..

[Salas]

Is there enough current through the Zener? Like 5-6mA? Measure drop on R5. You can use 6-7 pieces 2V LEDs instead, facing downwards in a string, and get about 12V too. Very silent.

[richie00boy]

Suspect duff C5 or C6 or zener.

[vibroverbus]

Originally Posted by Salas

Is there enough current through the Zener? Like 5-6mA? Measure drop on R5. You can use 6-7 pieces 2V LEDs instead, facing downwards in a string, and get about 12V too. Very silent.

Thanks - might try that alternative if I really can't get this to work (Plus it looks cool cause they lights up... heh heh just like my fuzz clipping LED's in a guitar amp)... But the "it SHOULD work" thing always drives me nuts and I'm too dumb and stubborn to give up until I figure out the "WHY" on stuff like this...

I'll measure the current for confirmation - other designs like this run much bigger limiting resistance like 3-6k vs. 2k but maybe sunthin funky about this setup or this zener or BJT... (maybe a ground loop putting AC on the base of the zener?)

Anyway thanks for the reply I'm brainlocked on like 12 projects a the moment making it hard to concentrate on common sense on any given one! Will post what I find...

[Salas]

Since you said you exchanged everything, I assume you don't have a faulty Zener, but maybe one that runs the wrong current for its wattage. Now if you got GND loop or some faulty part, then its another story.

[vibroverbus]

Originally Posted by Salas

Since you said you exchanged everything, I assume you don't have a faulty Zener, but maybe one that runs the wrong current for its wattage. Now if you got GND loop or some faulty part, then its another story.

OK I was right. Ground loop - weak ground on the board back to the chassis.

One of those 'measures good but must be impossible from how it works when it's running' things aka one of those 'when you push the probe against the pad it grounds out and measures OK but goes bad the minute you walk away' things. Works like a charm now. Just resetting a chassis screw when it was all said and done.

Originally Posted by Salas

Is there enough current through the Zener? Like 5-6mA? Measure drop on R5. You can use 6-7 pieces 2V LEDs instead, facing downwards in a string, and get about 12V too. Very silent.

Before I solved the mystery ground problem I jacked up the zener current a bit. It was at 8ma and the datasheet sample specs are at 9ma... Between that and all new caps and diodes and uprated BJT and uprated schottky rectifier in place of garden-variety should be massively improved at any rate.

Thanks for the input guys...

[Salas]

Happy end. Better than in Hollywood.