[sdiy] outlet as variac? calling all EEs...

[tomg@efm]

The real value of a variac is that you can bring a newly repaired
unit up to line voltage slowly. If you see excessive current being
drawn before you get to line level you know something is still
wrong and can go back in and fix it without causing more damage.

So the point is even though you are adjusting voltage you are 
trying to limit the current to keep something bad from happening.
I did audio for years and never turned on my variac unless it was
to stabilize line voltage so I could spec something out. 

The most valuable piece of test gear you can have is a 60W light
bulb wired in series with the equipment you are working on. This
allows the uint to run at full voltage but sucks all of the current.

When used on a power amp the lamp will glow bright as the caps
charge up and then dim to idle current. With pratice you can adjust 
amp bias by how dim/bright the lamp is.

For tube amps you might need a 100W lamp so the power supply
can get a little more current to start up with but it will then draw a 
fraction of the current needed to run transistor stuff.

This current limiting is a definate plus if you are sticking you hands
into a hot unit.

Tom