----- Original Message -----
From: Ian White, G3SEK <G3SEK@ifwtech.com>
To: <amps@contesting.com>
Sent: Tuesday, August 29, 2000 10:10 AM
Subject: Re: [AMPS] Testing HV Psu
>
> It depends why you want to do this. If it's to check that nothing
blows
> up if the supply is shorted, you only need to do it once or twice and
it
> doesn't need anything fancy.
>
> For that purpose, you could use a length of heavy insulated wire (no
> point in burning up a perfectly good screwdriver) already bonded to
> chassis. Also use insulated pliers to handle it, on the principle that
> several things would have to fail before putting you at risk. Steve's
> comment about goggles is a good idea too - at least do it at full
arm's
> length.
>
> BTW, 60uF is probably more smoothing capacitance than you need, by a
> factor of 2. This is a case where more is not better. The additional
> capacitance is mainly storing up energy and potential trouble if you
do
> have a flashover, and will stress the limiting resistor and the
> valve/tube more than strictly necessary.
> (Sorry it's a bit late to mention this, but sometimes we get sucked
into
> choosing electrolytics because they're available, rather than because
> they're the right value.)
>
> 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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>
>
Thanks Ian & Steve,
I should have made it clearer in my posting that the reason for doing
these tests repeatedly was to see whether anything blows up-particularly
the current limiting resistor which is the biggest unknown. 3 or 4 times
would be enough I expect although I have read somwhere, possibly on
AMPS, that each surge takes its toll and the resistor eventually can
fail unexpectedly.
I shall do the tests as suggested with an earthed wire, goggles etc.
I take the point about having excess capacitance. Originally, I settled
on 10 of these caps reluctantly as a compromise between excessive C and
the space needed. With a slight rearrangement, I can now accomodate 14
of them, which would bring the C down to about 43uF, a more sensible
value. I can see only advantages here, are there any drawbacks to using
such a long string of electrolytics? I just HAD to buy these caps 50 for
a fiver brand new, all have tested/re-formed perfectly so far, although
as you suggest, they weren't quite what I wanted....
Thanks & 73
Steve G8IZY.
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