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Help: Toroid choke for a preamp

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Hi All,

I am building a tube preamp and need 10-15H @ 100ma toroid choke for power supply. Believe it or not, can't find any reasonably priced. I contacted Toroid.com and they qouted one for $250!
I do appreciate if somebody let me know where I can get one.

One more question please:
I have 50VA toroid transformer. can I use it as a choke? It measures 9H with only AC current flowing through it. Will inductance drop significantly with 100ma DC?

Thanks a lot , Irakli
Toroids don't make great chokes since the DC tends to saturate the core. This means that a special gapped core must be used which is typically much larger. A conventional toroidial transformer will not work (I have tried it). A 1:1 isolation transformer will work, but not very well, if you connect the windings in series, out of phase, with a capacitor from the tap to ground.

If you must have a toroidial choke, try Plitron. They have them in their standard catalog, but the prices are not currently on the web. They are not cheap, but should be less than Toroid.com.


If you can live with a conventional choke the Hammond 158-M a 10 Henry 100 mA choke costs $16.50 USD at Antique Electronics.

Torroids make great chokes and I have designed plenty of them for military applications...
You don't need any special gapped core.....
The gap is distributed... You just need to choose the correct core material...
I wouldn't bother making one in your application.... Why not use a standard choke????

Thank you all for your response.

I was thinking that Toroid ckoke will give me less magnetic interference. After all, it is a preamp. But if you guys think that regular Hammond choke will work fine, I'll go with it. It's easy to get and not expensive at all.
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