On Fri, 16 May 2008, You wrote:

In article ,
Highland Ham wrote:

The crowbar is there to NOT blow up your equipment.

However operation of a crowbar should blow a fuse fitted 'upstream' of
the pass transistors. As already explained earlier in this thread ,the
crowbar should also be fitted 'upstream the pass transistors (but
'downstream' the fuse , while sensing the output voltage .

If the Astron voltage regulator would be suspect I would recommend a
very simple circuit with a 7812 voltage regulator and a PNP transistor
,its output 'steering' the pass transistors .

Ref : Experimental Methods in RF Design , by W7ZOI-KK7B- W7PUA
page 1.15


Instead of the 3 legged 7812 you can also use the similar LM317 enabling
output voltage adjustment
After all this is a homebrew NG

and if your really smart, you will dump the fuse, and replace it with
a Resettable Circuit Breaker, because Murphy's Law states the Crowbar
will do it's thing, ALWAYS at the worst possible moment, and the
appropriate replacement fuse will be a 5 miles drive away, at the
closest. You mileage may vary.....


Just to add, I've had a lot of problems with high amperage fuses, too, in
brick amplifiers and power supplies and VHF rigs with those "sexy" in-line
fuse holders. Seems like the connections become corroded, resistance goes
up enough that the current induces drop voltage high enough to do
significant heating...etc... Sometimes I've removed those fuses
completely, even in one brick amplifier (25-30 amps for a 3AG fuse!!) just
soldered a jumper wire across the &%$& fuse holder. Yeah, I know, bad
idea. But, all my problems went away.

Also, I had circuit breakers go bad, too. Brand new ones. Expensive ones.

KIS = keep it simple.