Ive found a good used choke that measures about 16H which is perfect for the tube amp im wanting to build.
Only problem is I have no idea on what current rating its rated at.
I need something that is rated at least 100mA.
TIA.
Only problem is I have no idea on what current rating its rated at.
I need something that is rated at least 100mA.
TIA.
Power supply filter chokes require special measurement techniques. Here's a couple of links that should be useful if you can adjust for the greater inductance values that you're interested in:
https://ludens.cl/Electron/lmeter/lmeter.html
Power Inductor Checker
https://ludens.cl/Electron/lmeter/lmeter.html
Power Inductor Checker
I don't think there is any easy way to determine the current capacity of a given choke. You have to make an educated guess based on overall physical size plus wire diameter or gauge if you can see it. Your estimate will also be based against other known chokes of like characteristics. DC resistance measurements of the winding can help narrow it down. The higher the resistance, the less current.
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It was tested on some fancy digital inductor tester that gave its reading on a screen, it came to 16H.
Ill check the DC resistance now and see what it is.
Ill check the DC resistance now and see what it is.
Most LCR meters don't apply DC current bias, so they cannot read a choke's working inductance correctly. That includes high-end models.
This is tiny and will never withstand 100mA DC bias. A suitable choke may have a mass of 1 pound or even more.
Figure its size and weight. Go on Hammond Mfg's site, find a choke of similar size/weight and DCR and slightly lower H. The known rating of the Hammond choke will be essentially the same as the unknown rating of yours.
You'll need to make a LC resonant circuit using a capacitor with a value you know precisely and the inductor will be your choke. You also need a current source feeding DC to your choke that won't oscillate. I'm successfully using a LED biased IRF610 wired into a CCS. Use a high power -> 2-5W 500R potentiometer for the current setting. You need to power the CCS with a good amount of voltage for headroom. A 30V regulated PSU is a good start. You'll also need a signal generator and an oscilloscope.
Apply Idc into steps and measure each resonant frequency value vs. Idc. Normally, it will increase vs. Idc. You can calculate the inductance using this formula:
L = 1 / (Fr*Pi)^2*4C
Note: A doubling in resonant frequency means the inductance decreases 4 times.
There will be a point where you'll increase current and inductance will sharply fall, in a non-linear way. This is the saturation of the choke and the place you want to avoid.
Try to avoid resonant frequencies above 400Hz. Testing the choke at high frequencies and the iron losses start to become into play.
Also, make sure the voltage across the LC tank is kept to 5V and above.
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picture shareApply Idc into steps and measure each resonant frequency value vs. Idc. Normally, it will increase vs. Idc. You can calculate the inductance using this formula:
L = 1 / (Fr*Pi)^2*4C
Note: A doubling in resonant frequency means the inductance decreases 4 times.
There will be a point where you'll increase current and inductance will sharply fall, in a non-linear way. This is the saturation of the choke and the place you want to avoid.
Try to avoid resonant frequencies above 400Hz. Testing the choke at high frequencies and the iron losses start to become into play.
Also, make sure the voltage across the LC tank is kept to 5V and above.
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