> ----- Original Message -----
> From: "Chris Wilson" <chris@chriswilson.tv>
> To: "Amps" <amps@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
19/12/2012 22:38
Thanks for your 2 replies Carl, and to Bill Turner. I think I will
abandon the idea of the resonant choke input filter and stay with the
previously successful capacitive input filter with a good old
electrolytic array. Some day I might have a play with these chokes,
but for now they sound like needless hassle and likely to add problems
with my level of experience. It was more a matter of having them, and
wanting to have a play, but I think I'll pass for now, and stay with
what worked on the other supply. Thanks for your time!
--
Best Regards,
Chris Wilson.
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