Looking to Accurately unwind larger Jantzen inductors to revised smaller values

[dtm1962]

Looking to make some existing larger value inductors to a lower inductance (unable to get the smaller values).

I have a Jantzen 0.025 mH 18 gauge inductor that I want to generate a 0.0095 mH value and I don't have the equipment to measure. I could guestimate via resistance (ie about 1/2 of resistance gives 1/3 of the inductance) but with the inductor only having not too many turns already, it will be critical that I am accurate & at the same time this is part of a series notch for a tweeter (aluminum) breakup mode >20Khz. SO it has to be accurate since the Q is very high= narrow peak.

Any help would be appreciated.

[Glowbug]

Know any friends who are into amateur radio? They might have an LCR meter you could borrow

[Dave in Green]

Here's some advice from John Krutke ( zaphaudio.com ) that may be helpful:

For unwinding a coil, the important thing to remember is number of turns is not a linear relationship to the inductance. Unwinding a .10 halfway does not equal .05 for example. Go to Lalena's inductor calculator ( Inductor Designer / Calculator ), enter the gauge, spool length and spool inside diameter for both a .10 and a .08 to find the number of turns for each one. Subtract the two and you'll know how many turns to unwind from a .10 to make it a .08. Note that this is very accurate but only works for air coil. Before you start unwinding, you can do a sanity check on the .10 by confirming known numbers like the DCR and outside diameter, with what the Lalena calculator shows up.

[dtm1962]

Thanks for the input. I will check the website out as well as possibly buying myself a LCR meter....