A choke input filter with sufficient L or a swinging version will improve
dynamic regulation over the typical commercial amps single C in any class of
service. They were used for decades, and still are, in Class AB and B
modulators.
My 1200W LK-500 SSB/CW amp with 26uF filter has a 400-450V swing on the
meter. My PP 304TL modulator with an untuned 20H choke input and 24uF of C
has a 200V swing. The only purpose of choke tuning was to be able to use
less inductance but there have always been reliability tradeoffs. Sometimes
bigger is better.
Carl
KM1H
----- Original Message -----
From: "Bill, W6WRT" <dezrat1242@yahoo.com>
To: <amps@contesting.com>
Sent: Sunday, February 21, 2010 12:57 PM
Subject: Re: [Amps] 120 Hz hum from Henry...
> 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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