Wire wound resistor - Printable Version
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Wire wound resistor - fields 100 - 07-11-2014
On one of my Philco sets the sectional wire-wound resistor (called B.C.resistor or voltage divider) even though having correct resistance between the sections is missing some insulation. Would like to have it replaced. In general, is it possible to sub the defective section or the entire unit with a non wound resistors, observing correct wattage, of course. If so, how to calculate that wattage?
Thanks.
RE: Wire wound resistor - morzh - 07-11-2014
Wattage is always U-square over R.
You know the voltages at the taps of each section and each section's resstance, so the difference of the voltage between any two pins (or the same measured directly as voltage between pins) squared over its resistance will be your disipation, then use a factor of at least two.
RE: Wire wound resistor - Mondial - 07-11-2014
If the resistor has the correct resistance and is fully operational, why replace it?
If it is the type I am thinking of, it is insulated with a winding layer of varnished thread. You can easily re-insulate by rewinding it with linen lacing cord it if it concerns you.
RE: Wire wound resistor - fields 100 - 07-11-2014
Mondial,
It looks like it has been overheated at one point or another and I can see the exposed naked wire. By re-insulating you mean running the lacing cord between the wire turns?
RE: Wire wound resistor - Warren - 07-11-2014
How about liquid tape. Would that work?
RE: Wire wound resistor - fields 100 - 07-11-2014
Not sure, it has to get between the turns. I will have to, while rewinding, maintain constant gap between them. Besides, there is a temperature issue.
RE: Wire wound resistor - morzh - 07-11-2014
I am not sure liquid tape is made to withstand heat.
On the other hand if the resistor exhibits correct reisitance, I would not as much as lift a finger.
RE: Wire wound resistor - Mondial - 07-11-2014
I would just wind a layer of cord on top of the resisistance wire, as was done originally. Under normal operation the resistor should never get hot enough to char the cord. In any case the previous overheating should have had no ill effect on the resistance wire itself
RE: Wire wound resistor - fields 100 - 07-11-2014
Morzh,
I am aware of the formula, my concern was the cushion factor.You think two is good enough, even in case of some possible short? I am not sure what happened with it in the past, perhaps something nasty,as the insulation went off on one section and the wire looks discolored , overheated.
RE: Wire wound resistor - fields 100 - 07-11-2014
If I just put layer of cord on the top, how will it prevent naked wire turns from touching each other and creating partial shorts, now or in the future?
RE: Wire wound resistor - Mondial - 07-11-2014
It never had any insulation between the turns, just the spacing between the turns. The wire should have been wound tight enough so the turns will not shift. The thread covering was just for protection.
Its just like a wirewound pot, the wire is not insulated, and each turn is isolated from the next by the spacing.
RE: Wire wound resistor - morzh - 07-12-2014
Fields
When I said "at least two", I meant exactly that, at least.
For small resistors I use three, for large - two. You could use whatever makes you comfortable, using higher power rating, the criteria being
1. Size. If it is big and fits, then
2. Cost. if it is not prohibitive, then
Use it.
RE: Wire wound resistor - GarySP - 07-12-2014
You might want to think about painting a coat of corona dope on it. Works to insulate noisy flybacks, should work on the BC resistor. Take care, Gary
RE: Wire wound resistor - morzh - 07-12-2014
How does corona cope stand to heat?
RE: Wire wound resistor - fields 100 - 07-12-2014
That's dope...