In article 949Ye.76228$Sj1.28811@okepread04,
wrote:
It's a 28 volt regulated 1 amp PS made by a long defunct pro audio
company.

Is it built into something or can random external equipment be connected
to it? If the latter, an output fuse might be a good idea.

It is internal, but looks like they might have used it on other products.

No LT fuses, only mains (240v, 250mA standard type.) which had blown.

My Tek 465M (and I assume other similar Tek scopes) have an interesting
approach. There is a regular mains fuse, then the transformer. On the
secondary, there is the winding, bridge rectifier, and main filter cap -
then another fuse before the regulator. I think that's kind of an
interesting place for a fuse.

Yup. I'd have thought before the rectifier would make more sense - since
as I've found failure there can take out the expensive bit - the
transformer. Although it's possible the correct mains fuse would have
failed first.

Now toroidal transformers have a high 'startup' current, so I'd guess
an anti-surge would be better at perhaps 125 mA? Is there a 'rule of
thumb' for mains fuses for such devices?

AoE 2nd suggests using "a slow-blow fuse with rating 50%-100% greater
than worst-case current drain of the instrument." I'm pretty sure that
"anti-surge" is rightpondian for "slow-blow". At 30 VA and 240 V, this
would suggest a fuse in the range of 188 to 250 mA.

Great. Thanks. Just what I was looking for. Couldn't find this in the
couple of text books I looked at.

Yes, IIRC anti-surge and slow-blow are the same. And even time delay?

And this isn't the first disc ceramic I've come across which has failed
short circuit. Better type?

Maybe Mylar or polystyrene? I'm not sure how much better they might be,
but those seem to be the other common types in similar capacitance and
voltage ranges to small disc ceramics.

OK. Strangely, the PCB hole spacing looked more for a Mylar than a disc.

Thanks once more.

--
*Very funny Scotty, now beam down my clothes.

Dave Plowman London SW
To e-mail, change noise into sound.