How about a thyristor in paralell with the hi voltage? You make a simple
STEPUP ignition transformer by simply passing the B plus lead through a
multiturn coil. An old idea from an old SHORT WAVE MAGAZINE article? The guy
who wrote it has been on this reflector and the article was part of a series
of articles on a K2RIW. Very complicated but very informative, I remember.
73s de Hans
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>Från: "Ian White, G3SEK" <G3SEK@ifwtech.com>
>Till: amps@contesting.com
>Ämne: Re: [AMPS] SB-220 Glitch Resistor ???
>Datum: tis 28 nov 2000 08.44
>
>
>Bob Johnson wrote:
>>
>>So my last mod before shooting the juice to the finals is to add the
>>"Glitch Resistor" !!!
>>
>>It has been recommended on this reflector that RFC-2 be replaced with a 15
>>to 20 Ohm real enamel wirewound resistor.
>>
>>My questions are:
>>Is 15 to 20 ohms "Cast in Stone" ?
>>Would 25 ohms be OK ?
>
>Not cast in stone.
>
>Eimac recommend a resistor that would limit the peak short-circuit
>current out of the power supply to 40A (for tubes up to 1500W
>dissipation). So for example, if the B+ is 2.5kV, at first sight the
>resistor would need to be 2500/40 = about 60 ohms.
>
>However, you can also "take credit" for the internal resistance of the
>smoothing capacitors, which allows you to reduce the calculated value of
>the glitch resistor. In practice 25 ohms will take most of the sting out
>of a current surge, so that's a typical value that people aim for. Some
>would go as low as 10 ohms, others a bit higher.
>
>>What wattage should be used ?
>>
>Enough to handle the full-time normal anode current with something in
>reserve, so I^2R would say a minimum of about 25W... but that isn't the
>whole story.
>
>>I have checked the Mouser catalog and they stock the OHMITE Series 270
>>Power Resistors in 15 and 25 ohms for the 25 Watt version (L25J).
>>
>I don't have that catalog, but the rule is to use a long-bodied resistor
>to avoid a direct arc from end to end. Having decided on the resistance
>and wattage, choose the longest resistor you can find.
>
>>If this resistor is suitable, would it be better to go with the 25 ohm
>>value on the basis that the peak discharge current would be lower or would
>>the higher resistance cause other unforeseen problems ?
>>
>Higher values give less peak current and more protection. Lower values
>waste less DC power and less anode voltage. It's a judgement call.
>
>Something often overlooked is that even if you fit a glitch resistor to
>handle current surges, there also needs to be some way of interrupting
>the power input from the mains. I've heard of situations where someone
>dutifully added a glitch resistor, but when the B+ was shorted the power
>supply kept right on going because the fuse/breaker ratings were set too
>high.
>
>Usually a step-start solves this problem, because it allows the mains
>fuse/breaker to be changed down to a rating only just above the normal
>operating current.
>
>You might also consider adding a high-voltage fuse, in series with the
>glitch resistor. In the past few years they have become easily
>available as microwave oven spares, complete in a shrouded holder with
>wire ends. Unfortunately the ratings only seem to go up to 1.0A, but
>that should be OK for a pair of 3-500Zs.
>
>73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> 'In Practice' columnist for RadCom (RSGB)
> http://www.ifwtech.com/g3sek
>
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>
>
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