Hi,

> > Let's not forget the dynamotor: an ac motor driving a DC generator.  For
> > extra isolation, use a rubber belt to connect the two.
>
> While your latter suggestions are getting a bit silly, the use of a motor/
> generator setup was indeed common in some applications, especially before
> the invention of good rectifiers.  In particular, many pipe organs circa

Often the Dynamotor was used in applications that worked from DC to AC.

These days our PICs and logic want low voltage DC and batteries come to
out aid, in them days there were only thermionic devices which
popularly needed some 100 .. 300V DC to work.  Dynamotors were used
in a lot of battery powered applications to step up typically 1.5V or
6V drycell batteries to 115V or 230V AC to drive mains apliances without
modification.

What was used in High voltage circuits where only low voltages were
available in DC such as in cars was another device called a vibrator
which was a can about 1" dia and 2" long that had what was mostly a
relay that would be made to cut its own power on energising so it
would buzz, mass added to the armature allowed the resonant mode of
vibration to be adjusted to 50, 60 or 400 Hz (or what you wanted
even a few kHz) and the vibrator would have some extra contacts that
could be used in a push-pull arrangement to drive a transformer with
alternating polarity.  This could be used to transform power or
signals and was how the earliest Chopper-Stabilised amplifiers
used to work at real low levels without drift as the signal was
converted to AC, then synchronously rectified (optional) that
would leave you with performance close to what we get out of a
cheap OP-AMP these days.

Cheers     *<<<-|
--
Kalle Pihlajasaari   kalle@ip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle