In addition to sensible advice so far, and linked to the turns ratio
thing...a transformer allows for thick, high-current output winding,
and thin (therefore compact, low-leakage etc.) primary. An
autotransformer could do the same but only by compromising the
advantages you state.

For high-quality hi-fi amplifiers, the harder saturation
characteristics of a torroid should not be a problem because you
won't get near saturation anyway. The best torroids are better than
the best EI, period.

cheers, Ian

"Jon Yaeger" wrote in message
...
Assuming that a tube amplifier can be built with a balanced output
(e.g. the
Zechendorff circuit), what are the pros and cons of using an
autoformer to
match output impedance vs. a standard transformer?

It would seem offhand that an autoformer could have sonic
advantages (e.g
lower losses, no coupling degradation, etc.). Would it cost less
to
manufacture? And finally, would a toroid be a suitable
implementation (I
am aware of toroid problems, especially with saturation, when used
for
standard output coupling).

TIA,

Jon