Today was tried for the first time at Pleiades lab a useable Pleiades (R,L) variable filter on big resistance and inductance.
The problem to overcome was hum because of using air cored (non ring would) multi tap indicators.
Using ring tape wound cores or ring ferrite cores creates on hum induced problem even at rooms with a lot of electromagnetic interference from electrical equipment.
The variable inductor box used is the brilliantly made Danbridge air cored decade inductor box D13A.
It's only disadvantage is hum as mentioned above.
But today another one came. The 2 are placed one on top of each other and connected in series but antiphase. 95% percent of gum disappears and a usable variable Pleiades filter results.
A Danbridge (0-1000Ω) decade resistance box with the fancy name DR4/ABCD was added in series to create the variable slope.
So in all L-L-R.
It takes time to learn how to effectively operate it.
The first mic tried is the Fostex M55RP 250Ω while singing The Power of Love.
A suitable set of values is 70Ω,40mH
The DR4/ABCD shows 50Ω but we have to take also into account the resistance of the coil as the Escort RLC digital impedance meter indicates.
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