Hmm, I wouldn't have said exactly that a choke is a constant current
device, but I get where Bill is headed. Choke input filters resist
changes in current because the choke inductance L induces a back EMF
(induced voltage) in response to any change in current. This induced
voltage tends to resist the change.
By contrast a big filter capacitor maintains the voltage, even as the
load changes. It does this because when the load decreases, the
capacitor dumps charge into the load to maintain the voltage. That's why
the voltage that backs up your computer memory can be maintained either
by a backup battery or a whomping big (e.g.,1F) capacitor.
There's a tendency with capacitor banks in power amplifiers to suppose
that more is better, for example that a 200uF filter is more desirable
than a 20uF filter. There are two schools of thought on this subject.
One is that the large filter cap will stabilize power supply voltage
better than the 20uF filter, and that is undeniably true. However, the
other school maintains that a smaller capacitor will result in a CW
signal which "thumps" slightly, as the power drops on each dot or dash.
Some folks like that sound, and I have to admit I kind of like it, too,
though I am sure purists will disagree.
Also, with large capacitors, there are the issues of safety and the risk
of damage from high surge currents. The stored charge in big capacitor
bank can store a ton of energy, and unless the amp is designed to handle
it (e.g.,with a carefully engineered step-start circuit) the result can
be serious amplifier damage
73,
Jim W8ZR
On 11/10/2018 4:35 PM, Bill Turner wrote:
------------ ORIGINAL MESSAGE ------------(may be snipped)
On Thu, 8 Nov 2018 21:43:02 -0800, you wrote:
Any comments would be greatly appreciated.
Jim VE7RF
REPLY:
You don't need a choke at all, at least for SSB or CW. A choke is a
constant-current device, exactly wrong for SSB and CW. Just bypass it
and be sure you have at least 35 uF of capacitance. Your SSB or CW
amps needs a constant voltage source, not constant current.
73, Bill W6WRT
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