• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

toroidal chokes

As I said in previous post, Tauscher in Germany can make custom DC chokes with iron powder cores and distributed air gap.

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And any other company which source iron powder cores from Micrometals.

Fixed air gap toroid GOSS cores/chokes are not standard products, they made only per customer specification/order. it is very unlikely any factory will mess with a couple of pieces.