[AMPS] HV PS topics
notawc@juno.com
notawc@juno.com
Sat, 15 May 1999 15:19:01 -0400
On Fri, 14 May 1999 00:42:36 -0400 "Dick Green" <dick.green@valley.net>
writes:
>
> > Figure it out yourself; all it takes is Ohms Law. The answer
> varies by
> > the application.
>
> Are you telling me to figure it out myself because you really don't
> know
> how?
No, just because it has been answered many times before. Check the
archives or Rich's web page OR ask someone privately. If none of those
work then going to the reflector is fine. Note that W4AN has mentioned
looking at the archives BEFORE asking questions so this is nothing new
and should come as no suprise.
Sure, Ohm's Law can tell you how to size the resistor for
> normal
> operation -- at 1.3A plate current, a 15-ohm resistor dissipates
> 25W. But
> Ohm's Law doesn't tell you how to size the resistor to survive arcs
> and
> long-duration shorts (if that's even possible.) When there's an arc,
> the
> entire 3200V of the HV ps appears across the 15-ohm glitch resistor,
> and the
> instantaneous current jumps to 213A. Obviously, there's not 682
> kilowatts of
> energy stored in the filter caps, and the current isn't really 213A
> (the
> ampere is defined as 1 coulomb of energy passing a given point in
> one
> second, and the arc and/or capacitor dump don't last that long.)
> Seems to me
> that the reason the glitch resistor survives is that the shorting
> event
> isn't long enough to heat the resistor to the point of failure.
Amen, you just answered one of your questions. Do you really need
confirmation every step of the way?
> Either the
> arc ends, the filter caps discharge, or the AC fuses blow before the
> resistor pops. So, the question is, when one of these events
> happens, just
> how much energy does the 15-ohm resistor handle, and for how long?
> How much
> is dissipated in the resistor and how much flows through the plate
> choke and
> parasitic resistors? I've gotta believe that this is a function of
> the ps
> voltage, resistor value, amount of energy stored in the filter caps,
> and the
> duration of the shorting event. Can you tell me those numbers?
More questions? I think it has become obvious that you have some of the
ability to figure it out. Since it is your amp, set up the various
scenarios and tell us what happens. You might want to reread the theory
on series and parallel paths.
How
> exactly
> did you decide that a 50W resistor would be adequate?
Very simple, it was the next higher size available in the catalog. No
rocket science required.
>
> > You remind me of someone else who spends all his time asking
> questions,
> > second guessing the replies, and spends most of his time going
> around in
> > circles.
> > Exercise your Extra Class License and have at it.
>
> This is uncalled for. You have absolutely no basis for making such a
> remark,
> and I resent it.
So. Where is it written that anything anyone says has to meet your
approval? Constructive criticism is where its at often on this reflector
if you havent noticed. Ruffled feathers notwithstanding.
,Some of us come to this reflector to learn. Others
> unselfishly educate us and earn our respect. The rest waste our time
> by
> posing as experts and making unkind remarks.
And this countrys education system is in shambles because of common
prevaling attitudes that fail to teach children how to think, work out
various scenarios to a problem and then present their answers to review.
I have no problem with aggravating some of the overly sensitive types if
it wakes up their ability to think on their own.
Dont take it personal. Or if you want to go to that level do it to me
privately.
I'll be happy to
> compare life
> accomplishments with you anytime -- then we'll see who has been
> going around
> in circles.
You dont even want to think about that my friend; you may be in for a
shock.
Cheers Norm
>
> Dick, WC1M
>
>
>
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>
>
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