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I got a pair of chokes that are of different inductances. One is about 6H and the other only 2H. The current capacity is 200ma. Which choke should I put first in a LCLC filter supply. What if I use a CLCLC supply, any difference in placement? BTW, the amp is SE pentode KT90 stereo with a 6sl7 driver tube.
I also have an 8H choke that is rated at 150ma. I read somewhere that in a LCLC filter the second L can be of lower current rating than the first, although, that doesn't make sense too me. Is this true? Thank you for your responses. Dak
Follow Ups:
How much current is needed - i.e what's the idle current of the KT90s?
As far as order, larger choke followed by smaller cap then smaller choke and larger cap will give a lower circuit "Q", and will have a better transient response - less ringing on a current step.
Eli's suggestion of a small input cap is essential. Without it, stored energy in the choke can be delivered into the reverse-biased diode, likely destroying it, on turn-off. The cap limits how high this voltage can go - I'd be inclined to use 0.1 uF myself - a 8 Hy choke carrying 150 mA stores about 0.1 joule (1/2* I^2 * L), and that amount of energy will charge a 0.1 uF cap to 1000V...
Hi TB, is the .01 cap required for SS rectification only? My amp has tube rectifier. In my amp I am using the first cap to help set the B+. With the .01 cap my B+ was coming too low. After trying different values 2.0uf was the value that comes up with the target voltage. cheers, Dak
2.0 μF. is large enough to take you out of critical current territory and the good regulation that goes with it. :> ( What vacuum rectifier are you using? A 5R4 drops a whopping 67 V., when delivering its 250 mA. maximum.
If you want critical current behavior, you need to find a lower forward drop vacuum rectifier or switch to SS rectified B+. The value of the "fudge factor" cap. needs to be under 1 μF.
Eli D.
DAK
With an LCLC filter use the 6H first
to get meet the critical inductance.
I would recommend downloading the PSUD program
or getting someone to do it for you.
Many factors are involved to get a
quiet and well regulated PS.
I could do it for you if you want.
I have alot of experience with this.
Post me off-line if this is your wish.
DanL
Hi DanL, I tried to down load the PSUD program once but my computer safety program (MacAfee) recommended against it. Anyway, thanks for tip.
What about the procedure using a smaller current inductor in the L2 position? cheers, Dak
Ignore MacAfee, the software is useful and safe.
Inductors intended for service at the I/P of LCLC filter must be hefty. They take quite a beating and are known to "sing". If you are going to use a choke that's not specifically rated for choke I/P service, you must derate its current handling capability. Derate by at least 50%.
The 2nd inductor is not subject to the stresses the 1st inductor endures. So, all you need is a part rated for the actual B+ draw.
When SS diodes are used to rectify the B+, protection against inductive kick back spikes is mandatory. A very high WVDC 0.01 μF. cap. in what would be the 1st position of a CLC filter provides the requisite protection. The cap. can help a little with "singing" too.
Eli D.
Thank you Eli, that is great information. I am starting to get a better understanding of how one should configure a CLCLC or LCLC power supply.
Is the .01uf cap a bypass cap or a in series cap. All of my previous CLCLC type filter have use 2.0uf or larger, up to 60uf , film caps. cheers, Dak
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