Transformer question (only slightly OT)

[Tony Duell]

> My father built himself a board which was similar but more elaborate:
> he could select among (1) a small (7.5W?) light bulb, (2) a large
> (100W?) light bulb, (3) a high-wattage heating element that was still
> under the breaker trip current for that mains circuit (an iron, I
> think), or (4) no limiter at all.

Another useful limiter (to repleace (3) in your setup is a 1000W tungsten 
halogen bulb (e.g. one of those 'security lamps'. They're pretty cheap 
now). 

The advantage of light bulbs is the postive temperature coefficient of 
the filament. THey have a low resistance when cold (and thus drop almost 
no voltage, often a small device will happily run with a bulb in series), 
but limit the current if there's a dead short. 

-tony