MIL-DTL-28778A
2.4 Order of precedence. In the event of a conflict between the text of this document and the references 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 First article sample. Prior to beginning production, a sample shall be tested as specified in 4.4
(see 6.3).
3.2 Temperature. The maximum operating temperature shall not exceed 105ºC at a 50ºC ambient.
3.3 Life Expectancy. The unit shall be capable of operating continuously for 10,000 hours.
3.4 Materials. The materials shall be as specified herein; however, when a definite material is not
specified, a material shall be used which will enable the transformer 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.
Substitution of materials. If the supplier desires to substitute another material for a specified
3.4.1
material or fabricated part, he shall submit a statement to the Government describing the proposed substitution,
together with evidence to substantiate his claims that such substitute is suitable. At the discretion of the Government,
test samples may be required to prove the suitability of the proposed substitute. Before such substitutions are made,
approval for each substitution shall be obtained in writing from the Government.
Flammable materials. Insofar as practicable, materials used in the construction of the
3.4.2
transformer shall be nonflammable and nonexplosive.
3.4.3
Corrosive materials. Corrosive materials used in any of the manufacturing processes shall
be removed or neutralized so that no corrosion will result from such use. Insofar as practicable, materials used in the
construction of the transformer shall be noncorrosive.
Insulation material. The insulation material used shall be selected to assure that the
3.4.4
temperature capabilities are at least 20º higher than the actual maximum operating temperature of 105ºC.
3.4.4.1 Laminated phenolic. Laminated phenolic materials shall conform to MIL-I-24768/17, ASTM D709, MIL-
I-24768/11, or MIL-I-24768/9. When electrical characteristics are involved, only natural uncolored materials shall be
used.
3.4.4.2 Molded phenolic or melamine. Molded phenolic or melamine materials shall conform to ASTM D5948.
3.4.4.3 Ceramic (external use). Ceramic materials, when used, shall be selected to enable the part to meet the
requirements of this specification.
3.4.5
Wire.
3.4.5.1 Magnet wire. Magnet wire shall be of the types and sizes specified in MW 1000 and shall conform to
the requirements of MW 1000. Government approval shall be required when other types and sizes of magnet wire
are used.
3.4.6
Solder and soldering flux. Solder and soldering flux shall conform to guideline 5 of MIL-
HDBK-454. Soldering types, other than those referenced in MIL-HDBK-454, and shall conform to ANSI J-STD-004,
J-STD-005, and J-STD-006. Government approval shall be required when other types of solder are used.
3.4.7
Screws, nuts and washers. All mounting and terminal screws, nuts, and washers shall be
corrosion-resistant material or shall be protected against corrosion.
3.5 Design and construction. The transformer shall be cased, hermetically sealed, welded, oil filled
and shall be mounted on a flat base. The base shall permit the transformer to be lifted and transported by fork lift
truck.
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