[Amps] inexpensive HV fuse

Roger sub1 at rogerhalstead.com
Wed Jul 22 18:00:22 PDT 2009

Carl wrote:
> Of course you could always employ the method detailed by John Lyles about 
> instantaneously (almost) dumping the capacitor bank in a 500KW amp!

Get someone to stand next to it, that has never had the honor of seeing 
how fast a crowbar can work.<:-))
Of course the Varistor route is also spectacular when dumping 50,000 
joules off a 480 primary that had the switching get out of sequence 
under load. Nothing left but the backing plate and two #6 wires standing 
straight out. If the supplies on either side of  you were working,  you 
always made sure they were not about to do any switching while you were 
in there. Those transformers were taller than I am and I've forgotten 
how many tones they weighed.  When using smaller rated GMOVs they need 
to be contained in a compartment or in some manner to keep the pieces 


Roger (K8RI)

> Carl
> KM1H
> ----- Original Message ----- 
> From: "Dave white" <mausoptik at btinternet.com>
> To: "Alex Eban" <alexeban at gmail.com>; "'Angel Vilaseca'" 
> <avilaseca at bluewin.ch>; <amps at contesting.com>
> Sent: Wednesday, July 22, 2009 10:15 AM
> Subject: Re: [Amps] inexpensive HV fuse
>> 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
>> -----Original Message-----
>> From: Alex Eban <alexeban at gmail.com>
>> Sent: 22 July 2009 12:14
>> To: 'Angel Vilaseca' <avilaseca at bluewin.ch>; amps at contesting.com
>> Subject: Re: [Amps] inexpensive HV fuse
>> Response time, guys!!!
>> Any thermally operated fuse is TOO SLOW to protect the tube.
>> Besides, the spring can carry many tens of Amperes before it heats up 
>> enough
>> to melt.
>> You'll probably blow up diodes and tube and God only knows what else!
>> Alex 4Z5KS
>> -----Original Message-----
>> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
>> Behalf Of Angel Vilaseca
>> Sent: Wednesday, July 22, 2009 9:21 AM
>> To: amps at contesting.com
>> Subject: [Amps] inexpensive HV fuse
>> Commercially available HV fuses are quite expensive.
>> I thought of using a small spring instead, like the ones in ball-point 
>> pens
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