Jack wrote:

Need to buy/make a dimmer for a 750 watt stage lamp.

My first thought is to just use a dimmer from box store and slice up an
extension cord and splice it in. That is assuming they have dimmers
to handle that load.. it would be easy to find a cord that would handle
that load.

Do they make 1000watt+ dimmers?

Is there a better solution. (light must be mounted about 25 feet away
from nearest power source, so need some bit of cord run.)

1KW dimmers are readily available, just a bit more expensive than the
$10 ones which are usually 600W rated. You didn't indicate what the use
is, but you can readily get lamps smaller then the "normal" 750W to fit
the fixture.

One of the 1KW dimmers mounted in a suitable enclosure will do the job,
but lacks some features of a proper stage dimmer such as linearization
of the dimming curve, EMI/RFI suppression, bulb preheat and smooth turn
on from 0%.

Pete C.