[sdiy] How to predict a transformer's current capability?

[jh.]

> If you want the ultimate transformer, get a donut, a toroidal transformer.
> Toroids do the best job of keeping the magnetic field where it belongs.
The
> core is powered iron for lowest eddy current. They seldom hum.

Yes, toroidals - I don't use anything else anymore.

BTW, if your country's mains supply voltage has been raised in recent
years (as it was raised from 220V to 230V in Germany), don't expect
too much from salvaging transformers from old gear. They are very likely
to produce excessive hum on today's higher voltage. The core is built
for a certain maximum magnetic field, and nobody would have used
more iron (bigger core) than necessary when the voltage was lower.
(Well, some have, but that's the exception.)

You probably won't blow anything with an "outdated" transformer,
but you're producing a much higher stray field which can induce hum
into your circuits or even produce mechanical hum in the transformer.

I have replaced a lot of transformers in analogue synthesizers (230V,
and mostly with a toroidal transformer), and cured a few hum problems.
In a way, recycling transformers from old broken gear is the exact
contrary ...

JH.