[Amps] Choke input filters, design criteria?

[Rob Atkinson]

yes the Henrys used resonant choke filters.  This helps explain it:

http://www.qsl.net/i0jx/supply.html

There was a nice article in QST in June 1946 about how to get the
inductance of a "mystery" choke using some math, a multimeter, an AC
microampere meter, and 120 v. service but since you have 240 you'd
have to work with one side of that if the UK has neutral return (four
wire service).

If you can get access to QST on-line:  "How Much Inductance?  A simple
method for measuring unknown filter chokes" by George H. Floyd W6OJK/2
June 1946 QST p. 69 and 132.

73

Rob
K5UJ

On Wed, Dec 19, 2012 at 8:14 AM, Chris Wilson <chris at chriswilson.tv> wrote:
>
>
>> 4 H is a bit low; 8 would be better.  Choke input filters are good for
>> power supply loads that are fairly constant, i.e. modes like AM, FM,
>> and RTTY.  Take a look at the designs used in earlier amps like the
>> Heathkit HA-10 as something to work off of, also the power supply
>> sections of 1 KW vacuum tube AM broadcast rigs.  Don't forget old
>> handbooks, West Coast and ARRL from the '40s and '50s.  if you are in
>> the UK perhaps RSGB has old handbooks with design criteria.  You could
>> start with an 8 uF oil cap.  Let's assume you are going with 3.5 KV.
>> Look for a cap rated for over 4; 4.5 KV or more is a good idea.
>> Follow that with the choke and another oil cap like the first one at
>> the input.  Don't fool around with electrolytics that will need to be
>> replaced some day--this is a filter that will last as long as you do.
>> Use the ratings of the choke as your guide.  Make sure the v. rating
>> of the caps is working volts DC.  Stay away from energy discharge
>> caps--a genuine filter cap will be bigger with sizable insulators on
>> the contact lugs.
>
>> 73
>> Rob
>> K5UJ
>
>
>
>
> 19/12/2012 14:03
>
> Thanks for the reply Rob. Is there a way to check the inductance of
> another choke I have? The other one is bigger, and is from a 3 phase
> supply for a Henry RF Generator. It gave just under 5kV at 1.5 amps.
> Henry use the same part number in both the 3 and single phase versions
> of the HV supply, but the single phase version uses 2 off 0.1uF
> resonating capacitors, and a 4uF filter cap, with fairly low value
> bleeder resistors. I believe these are to keep off load voltage in
> check? The Henry schematics show both supplies using the same part
> number of choke, but the 3 phase uses no resonance caps. The
> schematics don't give the inductance though.
>
> I believe an HV choke needs measuring for inductance with DC on it,
> for the purposes of use as a resonant choke, and making it resonant at
> twice the mains frequency (100Hz in this case, after a full wave
> bridge).
>
>
>
> --
>        Best Regards,
>                    Chris Wilson.
>
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