[Amps] inexpensive HV fuse

[mikea]

On Wed, Jul 22, 2009 at 03:15:46PM +0100, Dave white wrote:
> I concur.....
> 
> If you want to limit flashover damage use a high power surge limit resistor in the HT line between capacitor stack and plate choke, and use a fuse or overcurrent trip in the primary
> 
> There was a circuit in Dubus by OE5JFL which used optoisolators and other clever ideas to detect overcurrent and crowbar the ht away.  It seems a bit overengineered to me but I've seen it work well.
> 
> Like others are saying, fuses are too slow and you have no real idea of how a spring will behave.  Remember how much the tube costs and spend a few pennies on a surge resistor
> 
> Cheers
> Dave G0OIL

Ideally, if money were no object, we'd have power supply crowbars which
would let you put a piece of magnet wire from HV to ground, and which would
operate to keep the magnet wire intact after you pushed the "HV On" button.
These are used in power supplies for IOTs, klystrons, and other very high
power tubes. I really wonder just how low one could get the cost ... .
Anyone got prices on small Hydrogen thyratrons that'll stand off a few KV
and then dump multiple Joules in a big hurry?

In the meantime, the surge limit resistor and overcurrent trip in the
primary sound like a good starting combination, though even a good
overcurrent trip breaker needs milliseconds to open -- during which time
a tube can be severely damaged. Things go very bad very quickly when high
voltage is involved.

-- 
Mike Andrews, W5EGO
mikea at mikea.ath.cx
Tired old sysadmin