ORIGINAL MESSAGE:
On Sat, 20 Feb 2010 11:29:34 -0600, "Roy" <royanjoy@ncn.net> wrote:
> Read the article,
>noting the careful tuning to exactly the 120 Hz resonant frequency:
>http://www.qsl.net/i0jx/supply.html
REPLY:
In that article, the author states:
"There are however other approaches offering better regulation
performance (i.e. output voltage stability) at the expense of higher
complexity and cost; in particular the Input Choke Power Supply
(ICPS), in which a choke (L) is inserted between the diodes bridge and
the capacitor, as shown in Fig. 2."
That statement is true only in the case of a steady current draw (AM,
RTTY or FM). In the case of CW or SSB, a choke actually decreases the
dynamic regulation. A choke naturally opposes any change in DC current
flow through it and the result will be spikes in the voltage across
it, which are in turn applied across the capacitor and thus the
output. A large capacitor will absorb the spikes to some extent, but
can never eliminate them completely. A few minutes with a scope will
confirm this.
When AM became obsolescent, so did the choke-input filter. For today's
amps a simple C-input is best.
73, Bill W6WRT
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