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Old 10th September 2010, 08:38 AM   #1
Hubba is offline Hubba  Sweden
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Default Help replacing a PSU choke - How to choose choke

Hello,

I need help regarding chokes in a PSU. The PSU which I got uses a 10H/200mA choke, with a DC resistance of 36 ohm. I've got a 10H/200mA choke which is collecting dust in my garage, but the DC resistance rating is different (90 ohm).

As I am not en electrical engineer I do not have the skills to know if it is OK to replace the 36 ohm one with the 90 ohm one without doing any other modifications to the PSU. Could anyone please help, and if a mod is needed give me a hint about the math involved to calculate whatever is needed.

Cheers,
Fredrik
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Old 10th September 2010, 11:21 AM   #2
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Quote:
Originally Posted by Hubba View Post
Hello,

I need help regarding chokes in a PSU. The PSU which I got uses a 10H/200mA choke, with a DC resistance of 36 ohm. I've got a 10H/200mA choke which is collecting dust in my garage, but the DC resistance rating is different (90 ohm).

As I am not en electrical engineer I do not have the skills to know if it is OK to replace the 36 ohm one with the 90 ohm one without doing any other modifications to the PSU. Could anyone please help, and if a mod is needed give me a hint about the math involved to calculate whatever is needed.

Cheers,
Fredrik
The difference does not sound so big to me, but it does ofcourses depend on what kind of circuit your choke and powersupply feeds. If it is a preamp running on 50mA your B+ (supply voltage) will drop 54Ohm*0,05A = 2,7V. This is probably no problem.
If the circuit is a EL34 poweramp running on the full capasity of the choke the voltage will drop 54Ohm*0,2A = 10V. This is also most probably no problem, but you might like to test the bias of the amp if it has this option. If it is a self bias amp, the voltage drop will be adjusted for by the circuit itself and you will only loose a small fraction of output power.
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Old 10th September 2010, 02:33 PM   #3
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The short answer is the additional DC resistance of your replacement choke will drop a little more B+ voltage than the original (turning it into heat ), and the magnitude of the voltage drop depends on the current draw.

androokie summarized the math well.........Do you know the current that your circuit requires?

Looking at the Hammond 193 series of chokes as a rough reference, the 10H 193Q is rated at 500ma and has 53 ohms DCR and the 193J is rated at 200ma and has 82 ohms DCR.
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