[Amps] Filter Capacitors

[Jim Thomson]

-----Original Message----- 
From: Rob Atkinson
Sent: Tuesday, April 17, 2012 3:57 AM
To: Jim Thomson
Cc: amps at contesting.com
Subject: Re: [Amps] Filter Capacitors

On Tue, Apr 17, 2012 at 5:32 AM, Jim Thomson <jim.thom at telus.net> wrote:

>
> ##  any 2 x stage LC  filter in a power supply these days is plane nuts. 
> Any $$  spent on
> fixed and swing chokes is a complete waste of $$  imo.   Even the resonant 
> chokes used in the
> henry amps is a waste of effort.

This is just your opinion -- no facts presented.

%%%  No brainer here.  Just price out a new swinging choke, and a new fixed 
choke, along with the requisite
oil cap that goes between the 2 x chokes.    Then price out the 2nd oil cap 
that goes at the output of the
2nd choke.    Then price out the  plate xfmr.    The filtered  B+ on any 
choke input supply is  only 90% of the
Vac  across the plate xfmr.   So now you require a  plate xfmr with a 
secondary voltage that is going to be way
higher   vs  a simple C input filter.    Case in point, the henry 8k ultra 
uses a 6000 vac xfmr.  It runs  5400 vdc
no load.   That drops down to just 4800 vdc under a load of 1250 ma.   Not 
done yet.  The 8k uses  5 x 20k @ 100 watt
wire wounds in series for the bleeder.   That comes out to a whopping 300 
watts of bleeder power.   Or 60 watts
per bleeder.   Now a 100 w  wire wound, that’s dissipating  60w CCS  is 
going to get very hot.  If any of the bleeders
opens up, the no load vdc  WILL jump from   5400 vdc  to  8500 vdc !    Dahl 
did a roaring business selling replacement
plate  xfmrs and chokes for the 8 k.

%%%  You could replace all that crap with just a single  xfmr with a 3800 
vac sec and either one oil cap, or a string of lytics..
and you would not have the lousy V regulation either.



> ##  For XXX  amount of $$$  spent, you are much better off to just buy the 
> biggest hypersil
> C core xfmr you can get your hands on.....or an EI type  with real low 
> loss plates.  Then use enough
> C to get the ripple down to at least 1% or less.   Then you end up with 
> superb regulation, both static and
> dynamic.  On a  2 x GS35B 6m amp my buddy built, he tried using the bigger 
> plate xfmr, and just changed the
> taps on it.    With 5 kw   CCS CXR out on 50.125 mhz, the B+ drops exactly 
> 50 vdc  between  RX and TX.
> Ripple is real low, like .3%  with the 162 uf  total C used.  Ripple is 
> zip on 120-240-360-480 hz.
> The combo of high C + a bigger plate xfmr will result in good V 
> regulation.
> The low ripple is just the side effect of the high C...and amounts  to a 
> free lunch.   And no, it wont cook your xfmr either.

Here's an opinion for you:  162 uF at 5 KV is asinine.  I don't have
time to do the equation but I am pretty sure the stored  energy is
somewhere between 5000 and 10000 Joules.

%%%   5 kv @ 162uf = 2025 joules...so what.
When tapped for 7700 vdc no load, it then becomes  4800 joules.



Has your buddy had a plate
to grid arc yet?

%%%  No, why would he.


How long has this plasma generator been in
operation?

%% several years now. Thousands of hrs on the fil hr meter.

I hope he's at least using a couple or three large oil
caps and has bleeder backup.

%%  it consists of 24 x 3900uf lytics, each rated at 450 vdc.
Each cap has a 100k  @ 3 watt MOF across it.  Each cap
also has a 6A10  diode across it, RVS connected.  If any of the
eq resistors ever opened up,  the remaining caps  will still discharge!
Each cap has its own  100 kw @ 3 watt MOF directly across it.


I'd tell him to save the ridiculous
capacitance for his trunk speaker boomer--those things that rattle
windows when they go by outside.

%%%  162 uf wont work on a car stereo.   They all use  several FARADS when
placing caps across the car battery.  2-16  farads is not uncommon.



Make sure he has his amp completely enclosed with screen over the vent
holes so bugs can't get in there between B+ and chassis.

%%%    Screens ARE over the exhaust vent holes.  Air filters, panel type, 
are used on
the blower intakes.  It would take a BIG bug to span the gap between the B+ 
and chassis.
Worse case is  between chassis and top of RF plate choke bypass cap..which 
is a HT-57.
they are  1.89 inchs tall.

%%  he has  had several mishaps  during the construction of that and the 
other amps,
resulting  in B+  to chassis  or B+  to nearby metal.    HV fuse blew, that’s 
it.
He went through a total of  aprx  15 hv fuses  while debugging stuff on 3 
amps.  A lot
of it was dumb stuff, like stuff too close. or stuff that was partially 
taken apart to gain access
to something else, and left dangling.

%%  If an anode to grid arc occurs, the tube is probably toast anyway. The 
anode to
grid breakdown on the hi pot tester is typ  well over double the max B+ 
rating of the tube.
You can even buy chinese 3-500Z's that will hi pot test to over 12 kv.

%%  Now do it the normal way, with a low C filter..and with a 15-25 ohm 
glitch R and NO HV fuses....and tell me
which one is worse.   With the typ 15-25 ohm glitch R value that is 
advocated on this forum,
fault current is between double and triple what it would have been, had a 50 
ohm glitch R been used.
With no HV fuse, you now have nothing to  interrupt-shut off the sky high 
fault current..except the breaker
or fuse in the 240 vac line.   And by the time the 240 line is opened off, 
the damage has been done.  A good breaker
with a massive overload will typ trip open in 35 msecs.     Do it my way, 
and fault current is  between
one third to one half..... and the HV  fuse open up in less than 2 msecs.

%%  these high C filter setups have been tested from every angle you can 
think of.    Why use a long  string of
low C, 200-500 uf caps in a 3-7 kv supply, when  2000 uf to 10,000 uf lytics 
are readily available, new, on the surplus market.

Jim  VE7RF



73

Rob
K5UJ