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Re: [Amps] Choke anomoly

Subject: Re: [Amps] Choke anomoly
From: Jim Garland <>
Date: Mon, 12 Nov 2018 17:27:22 -0700
List-post: <>
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
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

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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