"Andre Majorel" wrote in message
...
On 2008-09-24, Arfa Daily wrote:
"Andre Majorel" wrote in message
...

Think I might as well increase the load until the transformer
becomes "too hot"...

If you do that, it might be the only time that you do, as it
may well have a thermal fuse embedded in the primary winding,
which will likely fail. Open circuit. Forever ...

Oh. My "too hot" threshold is probably at least 20°C below the
manufacturer's, though. g



By the time that transformer has got hot enough on the outside for you to be
getting worried, the windings in which the thermal fuse is buried, if indeed
it has one, will have reached the temperature necessary to open it. They are
quite delicate and it doesn't take much overload to **** them. I base this
assertion on 35 years of mending kit with them in.



What exactly is the issue with knowing the rating of this
transformer ?

Partly desire to learn what rules of thumb might exist, partly
that I'm going to reuse the transformer to power a few dual
supply circuits and want to know how much I can count on.



In the case of these little consumer-item transformers, rule of thumb is
about all you can count on. They are just about adequate for the job they
do, with everything working normally, which is all that the equipment
manufacturers need them to do. They are not too bothered about exact voltage
outputs or voltage sag, as they are invariably followed by 'good enough'
electronic regulation on the rails being produced from them. In the case of
your tuner, the current demand by the circuitry, will be pretty steady once
the processor has booted and all the filter caps have charged. If you want
to know what the transformer is good for, you could measure the current
drain on one of the secondaries with it running the tuner, and then add
another 30 to 50 %. I would be surprised if you couldn't draw an extra 80mA
or so from each winding, without serious sag problems. That's quite a few op
amps ...



Apparently, it is working, as you are able to measure
voltages. Worst case, you could just measure the primary
current with it running the tuner. If it's a 'typical' little
red transformer that is normally to be found in such items,

It does have red adhesive tape around the windings.



Ha! Knew it would ... d;~}



then just multiply the power consumption calculated from
measuring the input current, by about 1.5 to get a ballpark
figure for the transformer rating. When I say "ballpark", I
actually mean in the same county, but maybe not the same town
...

Thanks.

--
André Majorel URL:http://www.teaser.fr/~amajorel/
"Je regrette le Concorde. Au moins il vous amenait directement à
l'hôtel." -- Cyrano