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[Amps] FW: Power factor correction on tube amps

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Subject: [Amps] FW: Power factor correction on tube amps
From: "Jim Thomson" <jim.thom@telus.net>
Date: Sat, 9 Mar 2013 05:36:09 -0800
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Date: Thu, 07 Mar 2013 18:49:27 -0500
From: KA4INM <ka4inm@gmail.com>
To: amps <amps@contesting.com>
Subject: Re: [Amps] FW: Power factor correction on tube amps

On 03/07/13 18:07, Matt KM5VI wrote:

> Help me out here guys...

> I thought that conventional power supplies (transformer-bridge-filter) were
> relatively clean on reflected harmonics?

No, the transformer is all inductive and the diodes conduct for most 
of the sine wave, but not all, at that transition the current changes 
abruptly causing distortion.
(The capacitors are polar and not able to compensate for the 
inductance in the transformer.)
-- 
Ron KA4INM 

##  with a resonant choke set up, like used on the henry amps, PF is typ .9

##  On a high C filter,  you not only have  the ‘normal’ pf, but you also have 
loads
of odd  harmonics  up to the 9th.   So if you just measure AC line volts X  AC 
line current,
you will get VA power.  Trouble is the load is capacitive, by virtue of the 
high C filter. 

## One of the hams ( forget his call) used a HP PF analyzer  to look at the odd 
harmonics, and how
much current was in each harmonic,  it was just wicked.   When added to the 
fundamental, they
would be through the roof.   The only reason they are not is...  some of the 
harmonics  cancel, or
partially cancel each other....or are out of phase with the fundamental.   

##  I have tried off and on for years now to try and reduce the PF in  high C, 
HV supplies.   It’s extremely
tough to pull it off.   Even then, it will only partially  work for a 100%  
dead  cxr.   It won’t work on SSB, since 
the load is varying up-down like a yo yo.    You either have to cancel  out 
individual  odd harmonics...and / or
change the phase of the odd harmonics so they cancel with each other..and /or 
the fundamental. 
It’s the 3rd and 5th that are the biggest offenders.   You need equal amplitude 
+ opposite phase to cancel stuff out. 

##  In the end, I gave up and through in the towel.   I went through this with 
the late Peter Dahl, and I should have taken his
advice, don’t even try it, it’s an exercise in futility  with any high C,  HV 
supply.

##  Typ values  of PF are like .57   to .85   It’s all over the map really.  It 
doesn’t always get worse with bigger caps either.
Depends on  xfmr used.  The high Z types, originally intended  for choke input  
 supplies, with high dc sec resistance   don’t
fare too well.   The low Z types do a lot better..and the lower the dc 
resistance, the better, but not always.   There are other variables
at play here, including Z from pri of xmfr back to the source,  pri to sec C, 
whether the xfmr will even pass the odd harmonics, or
alter their phase etc. 

##  If you want unity-perfect PF use switching supplies that have pf correction 
built into them.   

Jim  VE7RF  
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