[Amps] power supply transformer

[David C. Hallam]

Commercial ham gear did the same thing in the past.  Look at some Johnson
schematics for their old transmitters.  Others did it, too.

David
KC2JD/4

> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
> Behalf Of Tom W8JI
> Sent: Wednesday, January 31, 2007 12:32 PM
> To: Dennis OConnor; amps at contesting.com
> Subject: Re: [Amps] power supply transformer
>
>
>
> > Paul, you have to have a line transformer for isolation -
> > it is life and death - no discussion possible...
>
> Not that he should do it (for other reasons), but there is a
> great deal of equipment we use every day that runs power
> supplies that are not isolated from the power line.
> The problem is getting the home builder to understand what
> to do to make it safe.
>
> Switch mode power supplies run directly across the power
> line, as do many TV sets and computer supplies. They do the
> isolation later, after the power line is rectified,
> filtered, and chopped back into higher frequency AC.
>
> In contrast to that there are many devices built by Hams
> that use transformers and are not safe. Some even appeared
> in the ARRL Handbook over the years. Just look closely and
> you will find many Ham projects that connect one side of a
> filament transformer primary or blower to the chassis.
>
> It depends more how you do things than anything else. If the
> neutral of the mains connects to the chassis it is not safe.
> This is especially true when the chassis is a common point
> for 120V systems like blowers, relays, or filament
> transformers.
>
> 73 Tom
>
>
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