"Phil Allison" wrote in message ...


"dave"

A Dim Bulb current limiter will protect better than a Variac. fyi.

http://www.kendrick-amplifiers.com/m...tegory_Code=04


** A Variac alone provides no protection.

But the method I outlined is vastly superior to the old light bulb trick.

Variac + true rms current meter + fuse (which can be a fast blow type).

There are far too many anomalies when a series lamp is fitted to the AC
supply.





I find the old lightbulb trick quick and easy, providing it is used in
appropriate circumstances.

Case in point being the bog standard small combo with the blown mains fuse I
used it on today, where it is a binary Yes there is a problem, or Not - the
fuse just blew.
And no harm done in the process, being as maximum mains current draw is 500
mA or so.
The amp will still run and make sound with the bulb in place.


I understand you can't use this techinique reliably on high power things
like Power Amps, cos they don't like undervoltage and will trip and
misbehave and do all sorts of weird stuff.
Here, I do use the variac in series with the bulb, just to see visually what
current is being drawn and how, and when.
And it is also sometimes useful to use the bulb as a soft start, then bypass
it, once you are happy the amp isn't going to explode.

Likewise I use the variac and bulb on SMPS's, again to visually and audibly
get an idea of whats happening and when.
You can hear when it kicks in, or shuts down, and that auditory information
is backed up by the behaviour of the bulb.



Horses for courses.


Gareth.