Manganin Wire

[ms660]

I have found a reference that said Manganin wire was sometimes used for the feedback winding in regenerative receivers to improve the smoothness of regeneration, has anyone tried it, was that ever used in a production receiver?

The reference was found in Babani's Coil Design & Construction Manual.

Lawrence.

[Herald1360]

Presumably the same effect could be got from a small series resistor. At any rate at LF/MF.

[ms660]

A bit of digging on the forum reveals that some Cossor valve superhets used resistance wire for the osc coil feedback winding on SW, I'm wondering why? Self damping?

Lawrence.

[G6Tanuki]

It's quite common to find resistors associated with superhet local-oscillator feedback-windings, particularly in cases where the osc is tuned over a large frequency-range by a large-value-swing variable capacitor. It's all to do with linearising the amount of feedback as the "Q" and coupling-factor of the osc coil changes as the L/C ratio changes. Without this, you will often find that there's rather too much feedback at one end of the capacitor's travel and not quite enough at the other!

Likewise, MF/HF superhets often have resistors across or in series with the signal-frequency tuned circuits to provide a more-uniform response across the tuning range.

Must admit, the idea of combining the 'resistor' with the windings themselves by using a form of resistance-wire is one that wouldn't have occurred to me but is a rather elegant solution!

Unwrap a dropper resistor for some wire.

[ms660]

Originally Posted by G6Tanuki

It's all to do with linearising the amount of feedback as the "Q" and coupling-factor of the osc coil changes as the L/C ratio changes. Without this, you will often find that there's rather too much feedback at one end of the capacitor's travel and not quite enough at the other!

That's more or less the conclusion I've come to, a bit more digging on web also suggests it helps to reduce the possibility of other oscillations, birdies etc.

Lawrence.

[kalee20]

Originally Posted by Herald1360

Presumably the same effect could be got from a small series resistor. At any rate at LF/MF.

Well, sometimes not!

MW and especially LW coils have many turns of wire, wound on more than one layer. So there is significant winding self-capacitance. And in a coupling or reaction winding this can cause self-resonance. Winding with resistance wire clobbers the Q of this, preventing funny spots across the frequency range.

Naturally, you wouldn't have the main tuned winding made with resistance wire! But auxiliary windings, yes.

[Brian R Pateman]

Manganin has a low temperature coefficient so maybe it had something to do with temperature stability.

[Herald1360]

Originally Posted by merlinmaxwell

Unwrap a dropper resistor for some wire.

That's probably nichrome, not manganin.