In article , Andres says...

I'm trying to rebuild a thermal evaporator. We need a power supply to
heat the boats (only precious metals and aluminum).

You need to have a high current transformer to do what you
want to do.

A very small alumina coated tungsten boat will take about
50 amps or so to get any decent rate. So the typical
routine for an inexpensive thermal evaporator is to
use a transformer that has a 120 volt primary and a
100 amp or so secondary. The transformer's primary
is then run off a variac to control the boat current.

Because the boat's resistance is a strong function of
temperature you need to ride the variac to keep the
rate more or less constant.

The easiest way to switch between sources is to ground
one end of each, and ground one end of the transformer
secondary. Then use a large aligator clip on the other
transformer lead to connect to the other lead of each boat
in turn.

Companies like Denton used to use us huge mercury switches
to switch between two sources.

You can net a bunch of parts if you can find an old Veeco
or Denton system. I myself has a tiny lab evaporator
made from a scrap denton that has been retrofitted with
a balzers turbopump. But it still has the original variac,
transformer, bell jar, and baseplate.

Jim

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