power supply diode confusion

Archived from groups: rec.audio.pro (More info?)

I'm troubleshooting the 6 volt side of a power supply for a BPM tube
mic. I have one failed (shorted) diode left to replace which goes to
ground, in parallel with a filter cap and .002 cermic cap. It comes
between the rectifier output and pin one of the voltage regulator
(7806). I assume the power supply should work without this diode there
at all, and I can't figure out why it's there. The rest looks pretty
much like a textbook power supply cicuit. Can anyone explain what the
purpose of this diode might be and what might be a replacement?

Archived from groups: rec.audio.pro (More info?)

Dan Mills wrote:
> apa wrote:
>
> > I'm troubleshooting the 6 volt side of a power supply for a BPM
tube
> > mic. I have one failed (shorted) diode left to replace which goes
to
> > ground, in parallel with a filter cap and .002 cermic cap. It comes
> > between the rectifier output and pin one of the voltage regulator
> > (7806). I assume the power supply should work without this diode
there
> > at all, and I can't figure out why it's there. The rest looks
pretty
> > much like a textbook power supply cicuit. Can anyone explain what
the
> > purpose of this diode might be and what might be a replacement?
>
> Are you sure it goes to ground?
>
> You sometimes see a diode between the output and input of a 78 series
> regulator to protect the part from its output going more positive
then its
> input (which can happen if there is lots of capacitance on the output
and
> some other load takes the input down quickly).
>
> The 78 series do not like this and tend to suffer....
>
> Just a thought.
>
> Regards, Dan.
There's one there too, but this one definitely goes to ground.

Archived from groups: rec.audio.pro (More info?)

Dan Mills wrote:
> apa wrote:
>
> > I'm troubleshooting the 6 volt side of a power supply for a BPM
tube
> > mic. I have one failed (shorted) diode left to replace which goes
to
> > ground, in parallel with a filter cap and .002 cermic cap. It comes
> > between the rectifier output and pin one of the voltage regulator
> > (7806). I assume the power supply should work without this diode
there
> > at all, and I can't figure out why it's there. The rest looks
pretty
> > much like a textbook power supply cicuit. Can anyone explain what
the
> > purpose of this diode might be and what might be a replacement?
>
> Are you sure it goes to ground?
>
> You sometimes see a diode between the output and input of a 78 series
> regulator to protect the part from its output going more positive
then its
> input (which can happen if there is lots of capacitance on the output
and
> some other load takes the input down quickly).
>
> The 78 series do not like this and tend to suffer....
>
> Just a thought.
>
> Regards, Dan.
There's one there too, but this one definitely goes to ground.

Archived from groups: rec.audio.pro (More info?)

apa wrote:

> Dan Mills wrote:
> > apa wrote:
> >
> > > I'm troubleshooting the 6 volt side of a power supply for a BPM
> tube
> > > mic. I have one failed (shorted) diode left to replace which goes
> to
> > > ground, in parallel with a filter cap and .002 cermic cap. It comes
> > > between the rectifier output and pin one of the voltage regulator
> > > (7806). I assume the power supply should work without this diode
> there
> > > at all, and I can't figure out why it's there. The rest looks
> pretty
> > > much like a textbook power supply cicuit. Can anyone explain what
> the
> > > purpose of this diode might be and what might be a replacement?
> >
> > Are you sure it goes to ground?
> >
> > You sometimes see a diode between the output and input of a 78 series
> > regulator to protect the part from its output going more positive
> then its
> > input (which can happen if there is lots of capacitance on the output
> and
> > some other load takes the input down quickly).
> >
> > The 78 series do not like this and tend to suffer....
> >
> > Just a thought.
> >
> > Regards, Dan.
> There's one there too, but this one definitely goes to ground.

Output to ground ?

Someone was just being very fussy. I've seen this on some ppl's schematics
before. Usually instead of the diode 'across' the regulator.

Graham