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.....

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete

On Fri, 16 May 2008, Tio Pedro wrote:

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete




Well, I've had a number of occurrences where, PTT on 2 M FM rig at current
well below current ratings and the output voltage goes to 0.5 or less and
had to off-on cycle the main switch. Makes me mad. Gotta get back to that
deep cycle 12 v battery.... They always go bad very very very slowly.
Great when there is a power failure, too! ;-)

Thanks to the rest of you guys that made comments, too.

"A" wrote in message
x.com...


On Fri, 16 May 2008, Tio Pedro wrote:

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete




Well, I've had a number of occurrences where, PTT on 2 M FM rig at current
well below current ratings and the output voltage goes to 0.5 or less and
had to off-on cycle the main switch. Makes me mad. Gotta get back to that
deep cycle 12 v battery.... They always go bad very very very slowly.
Great when there is a power failure, too! ;-)

Thanks to the rest of you guys that made comments, too.

You have stray RF in the shack. Check for intermittent connections to your
antenna. Most likely a bad shield connection inside one of the PL259
commuters or a bad ground connection.

"K4ERG" wrote in message
.. .

"A" wrote in message
x.com...


On Fri, 16 May 2008, Tio Pedro wrote:

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete




Well, I've had a number of occurrences where, PTT on 2 M FM rig at
current well below current ratings and the output voltage goes to 0.5 or
less and had to off-on cycle the main switch. Makes me mad. Gotta get
back to that deep cycle 12 v battery.... They always go bad very very
very slowly. Great when there is a power failure, too! ;-)

Thanks to the rest of you guys that made comments, too.

You have stray RF in the shack. Check for intermittent connections to your
antenna. Most likely a bad shield connection inside one of the PL259
connectors or a bad ground connection.

Stupid spell checker!

On Sat, 17 May 2008, K4ERG wrote:


"K4ERG" wrote in message
.. .

"A" wrote in message
x.com...


On Fri, 16 May 2008, Tio Pedro wrote:

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete




Well, I've had a number of occurrences where, PTT on 2 M FM rig at
current well below current ratings and the output voltage goes to 0.5 or
less and had to off-on cycle the main switch. Makes me mad. Gotta get
back to that deep cycle 12 v battery.... They always go bad very very
very slowly. Great when there is a power failure, too! ;-)

Thanks to the rest of you guys that made comments, too.

You have stray RF in the shack. Check for intermittent connections to your
antenna. Most likely a bad shield connection inside one of the PL259
connectors or a bad ground connection.

Stupid spell checker!


Not my idea but it sounded good when I heard it: "Life's too short for
spell checkers"

Ham radio advertisement many years ago: "Life's too short for QRP" and it
was for a big amplifier.

;-)

On Sat, 17 May 2008, K4ERG wrote:


"A" wrote in message
x.com...


On Fri, 16 May 2008, Tio Pedro wrote:

Unless there are other major failures, the crowbar simply
puts the Astron supply into current limiting. I've had
50-amp supplies running in current limiting for days
because of noise-induced SCR firing.

If the supply crowbars because a pass transistor shorted,
then the crowbar location becomes a rather mute matter;
and involves a bit more than fuse changing.

Pete




Well, I've had a number of occurrences where, PTT on 2 M FM rig at current
well below current ratings and the output voltage goes to 0.5 or less and
had to off-on cycle the main switch. Makes me mad. Gotta get back to that
deep cycle 12 v battery.... They always go bad very very very slowly.
Great when there is a power failure, too! ;-)

Thanks to the rest of you guys that made comments, too.

You have stray RF in the shack.

Not likely if you've been running the gear for years and didn't touch
anything. see my response to your second post.

Check for intermittent connections to your
antenna. Most likely a bad shield connection inside one of the PL259
commuters or a bad ground connection.

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.

On Fri, 16 May 2008 20:48:17 -0400, A wrote:
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.

If you are referring to those cheap, butt-contact, twist-and-lock
cylindrical fuse holders, I'll agree! They are problematic in many
instances, but especially so in high current situations.

I had no end of problems with the from-the-factory in-line fuse holder
with my IC-706. The IC-706 is a poor enough performer at voltages under
about 12.599999VDC, and the voltage drop across the fuse holder was
often enough to drop the volts into the rig even lower than that.

(Don't even get me started about the use of a butt-contact cigarette
lighter "power plug".)

I now replace that style of fuse/fuse holder with the automotive,
"horse-shoe" shaped style. (I'm sure there must be a more 'formal' name
for them.) You can even get them with weather proof caps for under-the-
hood applications.

And, for mobile operations, you can find replacement fuses up and down
the hiways and byways A WHOLE LOT EASIER than you can find the old
cylindrical fuses.

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
*** Killfiling google posts: http://jonz.net/ng.htm

: 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.....

The auto reset circuit breaker helps to start the fire, which takes out
the site/building. Not a good idea...

cheers,
s.