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RE: What tubes to use with this Interstage Transformers?

There is nothing crude about my measurements.

See this picture measure with only ac signal. The low frequency response depends very large on signal level ( i used different probes to get all in 1 picture).

was the transformer you measured airgapped to handle DC?

This behave is not present with a SE transformer with dc (at least a lot less).

I would expect that to some degree because in order to handle the DC offset an airgap is needed and the introduction of the airgap will temper any variation of permeability with applied signal. A proper test would be to measure the same gapped transformer at various excitation levels with and without DC current and then compare. I predict the transformer with the DC bias will never show more inductance (unless the DC is pulling shut an unstable gap)

TO clarify my statement I am saying it is normal for a gapped SE transformer to show a much smaller range of variation on inductance with applied signal and as signal is increased the inductance will also increase, however this behavior is not a function of applying DC but of the airgap needed to deal with the DC reducing the range of variability. The increase perm seen in all cases is simply due to the increased AC excitiation.

I am also saying that it is impossible for a DC bias on a core to increase the permeability of a core. It can in some cases increase the effective permeability of a core by manipulating the airgap but that is a simple mechanical issue.

dave


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