On 4/4/2011 9:03 AM, Paul Christensen wrote:
> So, left unmodified, older amps with 120V blowers are still a safety concern
> if they are serviced by only 3-wires. There's only one right way: Pull
> 4-wire, 240/120v service into the shack with proper conductor and breaker
> size, and replace the 3-wire power cord with a 4-wire power cord. The
> latter part is easy with Alpha 70/77 series amps.
There's another very good way to do it, as practiced by Ten Tec in the
Titan 425. The 120V blower runs across one half of the primary of the
high voltage transformer, and the center tap is not bonded to the
chassis. There's no good reason to bond the center tap to the chassis,
and in this case, it must NOT be bonded, because that would cause part
of the fan current to flow on the green wire.
This configuration is shown in one of the Power Point slides that are
part of my presentation on Ham Interfacing, also on the website.
73, Jim Brown K9YC
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