----- 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
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