On Wed, 28 May 1997 12:14:37 -0700 (PDT) Skip <mays@indigo.ucdavis.edu>
writes:
>
>Yes and no Carl,
>I don't consider it an exclusive DC portion of the power supply,
>although
>I get your point.
>
>Line filters are a wonderfull way to prevent problems, Mov's are nice
>but don't save the day every time.
I agree Skip about the alternatives.
It is a problem here with my response time since my JUNO mail provider
is a batch mode operation PLUS I only check once a day or so. My replies
may be a day or more out of date at times!
A spike on the power line will pop
>open or short an MOV, (I've seen both) and the next spike will take
>out
>the circuit if the MOV opened. This is not exclusive circuit
>operation,
>just some of the many horror stories I've seen close up. All dependant
>on
>the design of the power supply of course. Properly done, a shorted MOV
>
>would trip off a power supply, but some circuits need to "recycle" and
>
>stay in operation, trying to prevent damage as possible.
I believe that Ian covered MOV's better than any published version I have
read. His "memory" comments really hit home here since I have experienced
a high incidence of MOV failures....all GE and not floor sweepings
either. Maybe the hilltop and its lightning attraction has a "bit" to do
with it.
>Broadcast transmitters and Generation control circuits are a great
>example.
>A lightning storm in the Sierra Nevada is an exciting place to "watch"
>>the grid from a generator control room.
>The frequency responce of the Transformer plays an important role in
>my
>designs. I measured the responce of a Heathkit SB-220 fillament
>transformer years ago and found that it's design was especially good
>for
>inrush current limiting and a relatively low Fc.
The SB-220 filament xfmr was DESIGNED for low in-rush current. Anyone
modifying that circuit is wasting time and money.
>I'm not sure if the designers of the amp or the transformer planned it
>that way, but the transformer prevented more than one problem "out of
>the box".
See above...yes they did.
I do wish I knew who made the originals for Heath?
How many do you want?? No I did not provide the originals but the design
is no secret. I design/build/sell transformers up to 20KVA.
>The point I'm trying to make is that High frequency components do make
>it
>into the "DC" portion of a HV ps and that properly chosen bypass caps
>would seem to prevent more problems than they would cause.
We disagree here Skip. My input is that randomly selected caps can
actually generate a problem......sort of LF parasitics I am told. Don is
away in your area this week but I will ask him when he returns. My input
from him is that NO caps are the way to go...the diode does all the work
required.
>Please have your friend advise us why we might not want these
>capacitors
>in circuit. I'm always open to other opinions and ideas.
>thanks for your thoughts
>
>73's
>Skip May wv6f
73....Carl KM1H
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