"Gareth Magennis"

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.

** A bulb that passes 0.5A rms when lit will pass 8A peak at switch on.

That is no soft start.


The amp will still run and make sound with the bulb in place.


** Then you have to remove it and all protection is lost.


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.

** A valve guitar amp of over 100 watts will not warm up and run with a 0.5A
bulb in the AC.


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.


** A"soft start" is always provided when using a Variac.


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.

** You can stick with what you like and are used to.



.... Phil