> From: philk5pc@connect.net (Phil Clements)
> Subject: Re: [AMPS] Re: Bent filaments
To: <amps@contesting.com>
> Date: Mon, 14 Jul 97 05:16:57 +0000
Hi Phil,
Thanks for adding some intelligent comments to this subject.
> IMO the source of the current that bends the filaments is the same source
> that has sent Ip meters sailing out of their holes and across the room.
> It is the filter capacitor in the PS.
I agree totally. The filter capacitor is the source of the energy.
> to strike. Many posts have covered the fact that the old ways of protecting
> circuits from "big bang" events are far too slow for use in modern amplifiers.
Only a resistance is fast enough, and that resistance must be near
the source. How we get that resistance doesn't matter, it can be
distributed in the capacitors, choke, and other components or in
lumped form, but the resistance NEEDS to be there because nearly all
tubes arc at some time in their operating life cycle. And the
resistance needs to be in the high voltage supply line, not
downstream where several alternate arc paths could render it
ineffective.
> As amp manufacturers and home brewers began to push the envelope (no pun
> intended) with tubes running at maximum Ep and Ip there became less and less
> room (and time) for error. There now exists very cheap technology for removing
> the source of 99% of the "big bang" events by simply removing the PS filter
> cap. from the circuit in less than 3-5ms after a fault or arc occurs.
How would you do that Phil, within the market restraints of the
amateur radio market? Any time I run the numbers, I come up with an
added wholesale cost of $100-200. A simple energy absorbing
type resistor and the mounting hardware adds only about $20 to whole
manufacturing cost, and if you design that resistance into the
capacitors and choke you get it for free.
It's been my experience that filaments and grids are almost never arc
damaged in ~3000 volt supplies with ESR's of twenty ohms or so, but
are commonly damaged in PA's that make no effort to add intentional
ESR.
The worse situation imaginable is a large oil filled capacitor and a
RFC wound with heavy wire. Like you say, heavy-duty HV components
kill the tubes. But it is more a problem of ESR than capacitance
value.
> No sources = no forces.
>
> (((73)))
> Phil, K5PC
>
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>
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>
73, Tom W8JI
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