ORIGINAL MESSAGE:
On Thu, 10 Dec 2009 09:23:29 +0200, "Alex Eban" <alexeban@gmail.com> wrote:
>Third, most transformers are tested today by Hypot at 2500 VAC, so that
>actually they are tested at about our operating voltages.
>Actually, the reliability should be better because this design eliminates
>the bleeder resistors, since they are no longer needed to stabilize the no
>load voltage.
REPLY:
With this design, the bleeder resistor is still necessary to discharge the
capacitors. With no bleeder at all, those caps can hold a lethal charge for
days.
As for the Hypot testing, the 2500 VAC or so is applied for only a brief time,
perhaps a minute or so. That is better than nothing, but a far cry from having
the HV present for months or years on end. We all know of parts which withstood
an initial amount of HV and failed later on. HV never sleeps. :-)
This multiple supply design is rarely used in commercial ham amps for good
reason. There are too many parts waiting to fail and too much extra wiring. I
would strongly recommend saving your nickels and dimes and get a transformer
designed for the purpose. Do it right and you only need to do it once and it
will still be in use by your grandchildren. :-)
73, Bill W6WRT
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