Old news yes, but old dogs may want to learn from it. :>)
Reading the voltage swing on the plate volt meter is not looking at dynamic
regulation of the power supply. It is showing you the static regulation as
the meter is too slow to follow.
I highly recommend reading the articles from "GE ham news" that John K4PRO
referenced on power supply dynamic regulation. It spells out exactly what is
being talked about here.
Note in the article that with a 20 henry fixed and a swinging choke that
using a 45 microfarad capacitor still gave a dip in the high voltage. It
took around 90 microfarad to eliminate it. And that was on a 250 ma supply!
I have quoted Johns email here:
"There is some information here from the old GE Ham News, on power supply
dynamic regulation, on the AM Window:
http://www.amwindow.org/tech/htm/tutor.htm
Also a paper by Wallace Walhgren of the former Electro Engineering, now
Stangenes Transformers, on transmitter performance without filter chokes."
73
Gary K4FMX
> -----Original Message-----
> From: Carl [mailto:km1h@jeremy.mv.com]
> Sent: Sunday, February 21, 2010 8:17 PM
> To: garyschafer@comcast.net; dezrat1242@yahoo.com; amps@contesting.com
> Subject: Re: [Amps] 120 Hz hum from Henry...
>
> Thats old news, a couple of caps takes care of that.
>
> Carl
> KM1H
>
>
> > The choke will improve the "static" regulation but will kill the
> dynamic
> > regulation.
> > Hook a scope up to the HV and run some CW with your key. You will see
> > negative spikes in the HV. Same on SSB.
> >
> > 73
> > Gary K4FMX
> >
> >> -----Original Message-----
> >> From: amps-bounces@contesting.com [mailto:amps-
> bounces@contesting.com]
> >> On Behalf Of Carl
> >> Sent: Sunday, February 21, 2010 1:43 PM
> >> To: dezrat1242@yahoo.com; amps@contesting.com
> >> Subject: Re: [Amps] 120 Hz hum from Henry...
> >>
> >> 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
> >> > _______________________________________________
> >> > Amps mailing list
> >> > Amps@contesting.com
> >> > http://lists.contesting.com/mailman/listinfo/amps
> >>
> >> _______________________________________________
> >> Amps mailing list
> >> Amps@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/amps
> >
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|