[R-390] Power Supply, Capacitors, and Dead Horses

[Bob Camp]

Hi,

There is one other thing that keeps this from happening - the way the
transformer is constructed.

Prepare for long winded story .... it's the 390 reflector after all :) ....

Back a *long* time ago (as in before the 390 not an A) they invented a gizmo
called a transformer. Fairly soon it became apparent that the closer the
primary and secondary coupled to each other the better the transformer
worked. They started off with the coupling being in the 70 or 80% range and
worked up from there. Every couple of months somebody figured out a way to
bump it up by another percent or two and they each had their 15 minutes of
fame as a result. Playing with audio they got up above 90% coupling.

A bit later on (but still pre R-390 not an A) a guy named Edison and a guy
named Tesla had a little dispute about how to move power around. As a result
transformers became an even bigger item. The difference between 90, 98 and
99.999% suddenly looked like a *much* bigger deal than it had before. Now it
wasn't just bragging rights, but money (as in lost power) that was the
issue. They bumped things from 96 to 98 to 99 to 99.9% and started putting
things up on poles.

An interesting thing happened. The tight coupling transformers started
blowing up on the poles. Kind of an embarrassment if you know what I mean.
It was an early example of the device protects the fuse. The solution turned
out to be dropping the coupling back a bit and using the "loss" to current
limit the transformer. You had a little less efficient system but one that
was more reliable.

Fortunately they figured all this out before tubes came along so you are
pretty safe on very short duration surge current in power transformers if
it's a device that has tubes in it.

Now aren't you happy you asked ....

    Enjoy!

        Bob Camp
        KB8TQ



----- Original Message -----
From: "Scott, Barry (Clyde B)" <cbscott@ingr.com>
To: "R390 (E-mail)" <R-390@mailman.qth.net>
Sent: Thursday, March 14, 2002 9:23 AM
Subject: [R-390] Power Supply, Capacitors, and Dead Horses


> Sometime during the night last night, I happened to think of something
relative to the power supply filtering thread.  With a single cap across the
rectifier, when power is applied, isn't the current demand on the
transformer and rectifier components nearly infinite?  Is this a potential
problem?  Should there be some kind of current-limiting resistor (or other
component) in series with the cap?
>
> So far, it works okay and I realize this sudden current demand is short,
but is this something to be concerned about?
>
> Thanks again,
>
> Barry(III) - N4BUQ
>
>
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