[Amps] Choke input filters, design criteria?

[Carl]

----- Original Message ----- 
From: "Chris Wilson" <chris at chriswilson.tv>
To: "Amps" <amps at contesting.com>
Sent: Wednesday, December 19, 2012 9:14 AM
Subject: Re: [Amps] Choke input filters, design criteria?


>
>
>> 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.


Old ARRL and West Coast handbooks go into detail about "critical inducrance" 
and what happens when it is not enough. Going much higher offers very little 
benefit.

A tuned choke requires less inductance and Henry ran them for decades. The 
cap is critical and when they change or become leaky the light show is 
spectacular.

Carl
KM1H