What are these resistors good for? AP precision axial metal film


Paid Member
2004-12-26 9:38 pm
in the alps
I have two boxes of precision resistors from the 60's (says so on the boxes). From what I can tell they are made of a helical metal film on a ceramic body, with press-fitted endcaps and 5 cm (2 inch) leads. The ceramic body is about 2,5cm (1 inch) long.
The resistors are marked 0,5% and are rated 1/2W or 1W for the fat one. The values range from a few hundred to several M Ohm.
The thread spacing of the resistive element is roughly the thickness of a fingernail.
The logo reads A P with a plus-sign made of a horizontal bar and a lightning bolt.

I hooked one 300R 1/2W up to a variable PSU. At 1/2W dissipation it became warm, at 1W very hot, and at 2W the resistor/coating started smoking.

Has anyone come across similar devices? Where would you use them? Voltage regulators, anode load, generally in audio signal path,...? I'd guess they have considerable inductance/capacitance. What about voltage drop, how high would you go?

For size reference I've added a Vishay Sfernice MRS25 221k 1% 0.6W 350VDC resistor.


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