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KG6BAJ > NWSGRP 20.09.09 16:04l 56 Lines 2356 Bytes #999 (0) @ WW
BID : 11584_N1OES
Read: GUEST
Subj: Re: Power supply transformer advice
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Sent: 090920/0400Z @:KG6BAJ.#NCA.CA.USA.NOAM #:11584 [Grass Valley] InterGate $
** NEWSGROUP: rec.radio.amateur.homebrew
** FROM : Andrew VK3BFA <VK3BFA@wia.org.au>
On Sep 20, 7:43 am, Kenneth Scharf <wa2...@bellsouth.net> wrote:
> Andy GD1MIP wrote:
> > Hi I am building a (240volt in) 13.8 volt (out) PSU along the lines of
> > this plan..
>
OK, we are all being technical here - can I ask if the crowbar IC is
still available? Is the specified relay still available?
At an overvoltage condition,there will be over 200 watts being
dissipated in the 2r2 resistor in series with the SCR - hopefully it
wont instantaneously go open circuit....if the overvoltage protection
works, wont the thing go into cyclic oscillation as it attempts to
restart?....(not sure here, perhaps the gate never goes low enough for
this)
LM723 regulators tend to be a bit unstable - VHF ground plane type
construction is recommended.
The transformer ratings - the manufacturer rates them at a specified
current for a reason. For low duty cycle use, eg SSB, you can get away
with pulling more current. But a solid state Class C FM amplifier? -
also, as mentioned, there is very little headroom at 16v - 18v would
be better.....and thats assuming the mains input voltage is reference
quality - here in OZ, its a design variable, up to 20% fluctuations
are not uncommon, especially at the end of a long run.
Motorola 2N3055 transistors are fine - BUT- when the original Motorola
patents expired, and Motorola stopped making them, a lot of
substandard crappy ones (typically Eastern European) came onto the
market. Be warned, they can be unpredictable. TO3 is a pretty well
obsolete case style anyway. Good luck. And the Motorola symbol was
widely forged as well.
The above, of course, are my Neanderthal rantings on a newsgroup and
will no doubt start an impassioned debate on points of theory , or
maths, or how it was done in 1935. Remember, free advice is worth what
you pay for it.
But I would advise putting a 5w 15V zener across the output terminals,
and before that put a 30amp fuse. Minimal cost for added insurance.
Go for it - build it, experiment. Blowing something up is always a
fantastic spur to learn the correct theory for the application..if it
works first up, then its just a mechanical exercise.
Andrew VK3BFA.
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