[Amps] Choke anomoly

[Jim Garland]

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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