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[Amps] Capacitors vs No Capacitors

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Subject: [Amps] Capacitors vs No Capacitors
From: "Jim Thomson" <>
Date: Mon, 23 Apr 2012 07:43:02 -0700
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Date: Thu, 19 Apr 2012 22:47:55 +0100
From: Dan Mills <>
Subject: Re: [Amps] Capacitors vs No Capacitors

On Wed, 2012-04-18 at 18:15 -0500, wrote:
> Thinking out loud.....
> A 15KV @ 10 mf in a Broadcast FM transmitter many years ago shorted...........
> No noticable hum on carrier ( yes, I know .... FM )
> AM noise above FCC specs ?? Probably, but they were back on the air.

If the rig was big enough to operate on three phase power then there
would only have been about 30% ripple even without a cap in there, so I
am not at all surprised that an FM TX would work without a cap.

73s, Dan.

##  This  is why you don’t toss out old Orr books.    In the 19th edition, he 
3 x different configs of hv supplies, all using 3 phase.    The best one is 
called a 
6 phase bridge, and uses  6 x legs of diodes.   With just a tiny choke in the 
NO hv cap at all, the  ripple current is  4.2 %.    Ripple freq is  6F  or  360 

##  dahl made  a lot of these  6 phase bridges.    They look  just like a 4 x 
leg bridge,except
were wider, and had 6 x legs,  3 on top, and 3 below.   And both the single 
phase and 3 phase 
versions all used the same small boards,  which consisted of  8 x 6A10 diodes 
in series.   Each
diode had a mov across it.  These 6A10 s  were   1250 v  piv rated.   Each 
small board  was rated at
10 kv piv.    Your typ 6A10  will measure 1200-1400 v piv.   Since the didoes 
were 6A  CCS rated, 
the entire 3 phase bridge assy was rated at 18A  CCS.   In actual usage, that 
would run blazing hot,
unless air cooled.   Without the air cooling, his 3 phase bridge assys  are 
good for 6A  CCS.  

##  The higher voltage rated assys  simply used more small boards wired in 
series, like 3+  boards PER
leg, and 6 x legs  in total.   The biggest one I saw that he made for 3 phase 
used 12 boards per leg, 72 x boards
in total.  rated for 40 kv at 18 A  CCS.....and all done with just  6A10 
diodes.   720 kw CCS...with air cooling.
That  assy was 18 inchs wide x  3 ft tall..and not very deep, perhaps  10 
inchs.  All the various frames  and divider 
walls  were made from that red micarta sheeting.  He used the same sheeting, 
for the smaller single phase FWB,s 

##  I see in another tech note that another config has been used, called a 12 
phase bridge.  The ripple is so low,
no cap at all is required.   I think Harris employed it for air craft use. 

##  for those lucky folks who have 3 phase power in their shack, like our 
european friends, ripple freq is
still 6F, which is 300 hz in their case, since they have 50 hz power.  Being 
able to  Top up the caps  300
times per second, instead of the usual 100 times per second is a huge 
advantage.   You can  then get away with
a small filter cap.    In NA, that would be topping the caps  up at 360 times 
per second, instead of 120. 
And only 60 times per sec if a doubler is used.   A  3 Phase plate xfmr + a 6 x 
phase bridge, and one small filter cap
would be the ideal ticket.   Plan B is just a single phase xfmr, the usual FWB, 
and a bigger cap. 

later... Jim   VE7RF 
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