Mark
That crowbar looks to be a good idea. Wolfhard Merz of DESY in
Germany has built a light triggered series thyrister CB to protect
klystrons at even higher voltage. His paper can also be found online
at the 2003 PAC conference or the 2004 EPAC conference.
All of the crowbars I deal with use either Ignitron or spark gap for
the shunt element. I am in the midst of designing a new one right
now, and was thinking of the same old mercury ignitron. For several
kiloamps at 30 kV, its hard to beat, although silicon devices are
coming closer as both the DESY and ASTEC projects have demonstrated
to the world.
I suppose you won't need more than one or two of the GTO or
thyristors in series for your power supply? You can get IGBTs for ~5
kV rating now, but would need a way to hold them latched until the
capacitor is drained. Also expect to pay a lot of money, probably
more than your amplifier costs.
73
John
K5PRO
>
>Message: 3
>Date: Thu, 20 Jul 2006 17:24:20 +0100
>From: Mark Hill <g4fph@mjha.co.uk>
>Subject: [Amps] Crowbar that HV!
>To: Amps Reflector <amps@contesting.com>
>Message-ID: <7.0.1.0.2.20060720170234.0380daa8@mjha.co.uk>
>Content-Type: text/plain; charset="us-ascii"; format=flowed
>
>Folks,
>
>Talking of protection. I'm contemplating building an crowbar for the
>HV supply in my 3CX3000A7 PA.
>
>The PSU filter capacitor is really too large (130 uF) and the amount
>of energy it holds when charged to 5 kV is frankly scary. Eimac's
>AB17 seems unclear about how much of a bang this valve can take (4J;
>50J; something in-between?). I'm not sure whether my ear drums would
>be OK under conditions of flash over either!
>
>I found an interesting article here:
>http://www.astec.ac.uk/rf/rf_preprints.htm (a little way down the
>page there is a PDF file entitled, 'A Solid State Crowbar for RF Tube
>Protection').
>
>I like the way that the series thyristor combination appears to have
>been driven, i.e. individual current transformer for each device with
>a common primary turn through them all. Has anyone tried this
>technique? Seems as if it might be cheaper and potentially more
>reliable than a bunch of opto couplers and transistors etc. Is
>anyone on the line using a crowbar of any description?
>
>Regards.
>
>Mark.
>*******************************************
>Mark Hill - G4FPH
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