MIL-PRF-39002 Resistors, Variable, Wirewound, Semi-Precision, General Specification ForThis specification covers the general requirements for semi-precision, wirewound, variable, resistors having a resistance element of wire, wound on an arc shaped insulated form, so that a contact bears uniformly on the resistance element, when adjusted by a contact shaft. The electrical output \(in terms of percent of applied voltage\) is linear with respect to the angular position of the contact arm. These resistors are capable of full-load operation \(when the maximum resistance is engaged\) at a maximum ambient temperature of 85 Degrees C, and are suitable for continuous operation, when properly derated, at a maximum temperature of 135 Degrees C. These resistors have a tolerance of ??5 percent.

Pages 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12 - 13

MIL-PRF-39002C

(Copies of these documents are available online at https://assist.daps.dla.mil/quicksearch/ or from the

Standardization Document Order Desk, 700 Robbins Avenue, Building 4D, Philadelphia, PA 19111-5094).

2.3 Order of precedence. In the event of a conflict between the text of this document and the reference cited

herein (except for related specification sheets), the text of this document takes precedence. Nothing in this

document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained.

3. REQUIREMENTS

3.1 Specification sheets. The individual item requirements shall be as specified herein and in accordance with the

applicable specification sheet. In the event of any conflict between the requirements of this specification and the

specification sheet, the latter shall govern.

3.2 Qualification. Resistors furnished under this specification shall be products that are authorized by the

qualifying activity for listing on the applicable qualified products list before contract award (see 4.4 and 6.3).

3.3 Materials. Materials shall be used which will enable the resistors to meet the performance requirements of this

specification. Acceptance or approval of any constituent material shall not be construed as a guaranty of the

acceptance of the finished product.

3.3.1 Pure tin. The use of pure tin, as an underplate or final finish is prohibited both internally and externally. Tin

content of resistor components and solder shall not exceed 97 percent, by mass. Tin shall be alloyed with a

minimum of 3 percent lead, by mass (see 6.10).

3.4 Interface and physical dimension requirements. Resistors shall meet the interface and physical dimension

requirements as specified (see 3.1).

3.4.1 Resistance element. The resistance element shall be resistance wire, wound on a suitable form which shall

not char or break down as a result of the tests specified herein. The element shall be a continuous unbroken length

of conductor without joints, bonds, or welds, except at the junction of resistor element and the winding terminals.

3.4.2 Protective housing or enclosure. The resistance element of completed resistors shall be protected by a

housing, or an enclosure, or both, which shall completely cover the exterior of the resistance element. The protective

housing or enclosure shall be free from holes, fissures, chips, or other faults, and shall be such as to minimize the

establishment of leakage paths between the terminals resulting from collection of moisture film on the exterior surface

of the housing or enclosure. If the housing is made from an aluminum alloy, it shall be properly protected against

corrosion and all fasteners shall be suitably plated. Unplated copper-alloy metals shall not be used in contact with

aluminum.

3.4.2.1 Nonturn device. A nonturn device shall be furnished which will prevent rotation of the resistors with respect

to the surface on which they are mounted. The nonturn device shall be permanently fastened to the resistor body

and shall be located as specified (see 3.1).

3.4.2.2 Standard and locking bushing. Standard or locking bushings shall be as specified for the applicable style

(see.3.1).

3.4.2.3 Hardware. When specified (see 3.1), each resistor shall be furnished with a corrosion-resistance (see

3.22) hexagonal mounting nut, a corrosion-resistant internal tooth lock washer; and when applicable, a locking nut not

assembled on the resistor, unless otherwise specified (see 6.2). For direct Government orders, hardware shall be

assembled on the resistor. When applicable, the dimensions of the hardware shall be as specified (see 3.1).

3.4.3 Operating shaft. All operating shafts shall be made from corrosion-resistant metal.

3.4.3.1 Style. Operating shafts shall be slotted (see 3.1). In no case shall the slots of slotted shafts be deep

enough to interfere with shaft retainers or bearing surface.