02-14-2013, 07:56 PM
In the pushpull cascade when both halves of the primary exhibit similar (not equal) resistance to the Ohmmeter, this is good (albeit not 100% guaranteed) indication that the primary is OK. The inequality (about 10% or so) in the DC resistance is due to the fact that the second half is simply longer, being wound over a larger diameter of the first half, which in turn would on a slimmer bare bobbin.
As the real impedance (reactance) is determined by more or less the core size and the number of turns, the two reactances will be equal. The total impedance will be very close as the reactance will be order of magnitude larger than the DC resistance. And they are not added together but their squares are, and then the square root is taken.
Of course you can have a short turn which will not change (not necessarily) the DC resistance but will bring the reactance down to almost zero.
But first you have to establish you don't have a case of the open winding, and your ohmmeter is your best tool for that.
As the real impedance (reactance) is determined by more or less the core size and the number of turns, the two reactances will be equal. The total impedance will be very close as the reactance will be order of magnitude larger than the DC resistance. And they are not added together but their squares are, and then the square root is taken.
Of course you can have a short turn which will not change (not necessarily) the DC resistance but will bring the reactance down to almost zero.
But first you have to establish you don't have a case of the open winding, and your ohmmeter is your best tool for that.
