V72 Humbucker Choke

[CJ]

here is a pic showing how DC current effects the BH curve,

when the plate choke has a DC bias, it will generate a force H-dc,

this will generate a flux B-dc,

so the starting place for the  BH curve is offset up and to the right,

this offset will mean that the positive half cycle of the AC signal will differ from the negative half in that the positive half is trying to tilt the steel molecules after they already have been pre-tilted by the DC, so it is harder to tilt them and thus, harder to magnetize the core which means less perm than when the negative half of AC signal magnetizes the core, Incremental perm will therefore vary during the cycle.

so with the biased inductor there is an asymmetry with respect to the B-H axis,
this results in an absence of half-wave symmetry in the exciting current,
harmonic currents according to Fourier analysis will therefore contain even as well as odd multiples of the exciting frequency.

another distinctive feature is a markedly reduced slope of the loop, the size and slope of the loops shown will depend on the magnitude of the excitation voltage as well as the bias H-dc. The large AC signal in the first pic results in a large delta B and also produces a large delta H.

the smaller AC signal and sall delta B in the bottom pic are characteristics of the core behavior in the capacitor input DC smoothing choke.

 

[CJ]

here is a BH curve for an inductor with no DC, just for comparison to the DC curves,

it has a couple of important points noted on it such as initial permeability and max permeability,

good reading on DC and BH loops here>

http://www.vias.org/eltransformers/lee_electronic_transformers_04_15_01.html

 

[vinyvamos]

This thread is incredible CJ, so much data you have brought forth there. And now that I have dug up this dusty paperwork, let it be a reminder of your large contributions to the forum, and MANKIND... (reaching for my coat...)

 

[Winston OBoogie]

Wow! Great stuff CJ. and Abbey. I was AWOL when the thread was active and only just saw it after a search re the V72 choke.

I'll need to re-read this multiple times to grasp a lot of it but, for future reference for others that come along, the choke I'd sent CJ with the bright lams was from an EMI V72S module.

Interesting to see the difference against the other original that was tested with darker lams which, I assume, was from a standard NWDR V72.