----- Original Message -----
From: "Bill Turner" <dezrat1242@yahoo.com>
To: "Amps" <amps@contesting.com>
Sent: Monday, December 17, 2012 10:35 PM
Subject: Re: [Amps] Choke input filters, design criteria?
ORIGINAL MESSAGE:
On Mon, 17 Dec 2012 17:36:26 +0000, Chris wrote:
I am
wondering if I should attempt to use it rather than a capacitive input
filter?
REPLY:
Choke input filters are a holdover from the old AM transmitter days
when current draw was relatively constant and HV capacitors were
expensive. Today's amps for SSB and CW need a constant voltage source,
not a constant current one. If you use a choke in a power supply where
the current draw varies a lot, you will see the output voltage
swinging widely, just what you do not want.
Toss the choke. Capacitors only.
73, Bill W6WRT
BCB transmitters often run the Class AB thru B modulators from the same PS
as the Class C final so there is certainly a wide current variation.
Voltage regulation is helped by the combination of the Class C load and
value of the input choke.
Hams can use a choke to limit an otherwise too high B+ and/or to be able to
use a high impedance old style transformer. The DC resistance of those
transformers is also much higher, often a factor 0f 10-20 or more.
With a sufficient choke value and constant current load to substitute for
the Class C final such as a healthy bleeder resistor, they can be used on
ham CW/SSB. Not very efficiently tho. In the old days the HV PS was
controlled by a toggle switch or PTT activating a relay in the transformers
primary. This did away with a big part of the resistive load. Certainly not
very practical for VOX, QSK, etc, but fine for PTT or a foot switch.
Carl
KM1H
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