[Amps] FW: Power factor correction on tube amps

[KA4INM]

On 03/07/13 19:50, Jim K9YC Brown wrote:

> On 3/7/2013 3:07 PM, KM5VI wrote:
>> I thought that conventional power supplies (transformer-bridge-filter)
>> were
>> relatively clean on reflected harmonics?

> Nope! Power line harmonics are the result of current flowing in
> relatively short pulses at the positive and negative peaks of the 60 Hz
> cycle to charge the input filter capacitor, which is used in both linear
> and switch-mode power supplies.

> It's quite simple -- capacitor input filter => strong harmonic current
> on the mains power line. These are harmonics of the mains power
> frequency, either 50 or 60 Hz, depending on where you live.

> What switch mode power supplies add is RF noise -- they start with
> rectified DC to a capacitor input filter, then use that DC to generate
> square waves at a much higher frequency (typically 10-20 kHz), then
> rectify and filter that to feed the equipment. The RF noise consists of
> harmonics of the square wave, modulated by random noise added to
> "dither" (frequency modulate) the square wave. Dithering is a sort of
> "cheat" to get around EMC regulations (FCC, and EU) -- instead of a
> strong carrier at each harmonic, the noise is spread over a wider
> bandwidth. The result is "humps" of noise that slowly drift up and down
> the band with a weak carrier in the middle of the hump.

   So you are saying our tube HPA's hV power supplies have a near unity 
power factor?
-- 
   Ron  KA4INM - Youvan's corollary:
                 Every action results in unwanted side effects.