On Wed, 12 May 1999 21:27:19 -0400 "Dick Green" <dick.green@valley.net>
writes:
>
> While we're delving into glitch resistor design theory, how about
> some
> practical advice? Before replacing the plate choke, I'm going to
> install a
> glitch resistor in the LK550 I've been working on. KM1H suggests a
> 15-ohm
> 25W enamel wirewound. I found what appears to be a suitable part
> from
> Newark, an Ohmite 02F2280 ceramic core wirewound resistor with a
> flame
> resistant vitreous enamel coating. It's one of those tubular types.
> There's
> a mounting bracket available that appears in the drawing to be a
> piece of
> metal that goes through the hollow tube of the resistor and has
> mounting
> tabs at both ends. It looks like the bracket will hold the resistor
> up off
> the chassis by at least 1/4", positioning the solder lugs straight
> up. It
> looks like a nice way to install the resistor, but is there any
> problem with
> using this type of bracket? Does it hold the resistor rigid so that
> it won't
> roll around? If it's not suitable, what alternative mounting methods
> are
> popular for this type of resistor when used for glitch protection?
Mounting on a pair of ceramic insulators was suggested earlier if I
'member.
The factory clips may be OK but never remember seeing a real life voltage
rating between the resistive element and the mount stuck inside the
hollow core.
>
> What's the typical result of a high-current failure in a resistor
> like this?
> Does it come apart in such a way that the lug soldered to +HV could
> come
> loose and contact the chassis or short to the chassis through the
> bracket?
Brown out to light grey in the core and eventual opening of the resistive
element. Takes a LOT to make that happen. A few millisecond HV PS
discharge should not blow a 15 Ohm 25W resistor as used in a fairly
legal limit ham amp.
As suggested by KM1H do not use a cement resistor. If in doubt go to a
50W.
Norm
> 73, Dick, WC1M
>
>
>
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>
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