Cal-R

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The resistor on the side of the ghost trap is a small, wire wound type encased in an aluminum heat sink. It was made by Cal-R Inc., designed to the military specification MIL-R-18546/1G. The MC250, as identified on the side of the trap, adheres to an RE70G style Mil-Spec resistor. These resistors come in a wide variety of resistances, but they are always dimensionally alike and are 20W power resistors. Key dimensions to look for are the hole spacing, which are 0.719” x 0.781” apart. The MC250 is also around 0.562” tall and the body is about 1.062” wide minus the solder lugs. Do not be confused if someone tries to sell you a different style of Cal-R. They are not all the same. For example, an MC80 is a 5W resistor, meaning it adheres to the RE60G specifications. The MC80 mounting holes are around 0.25-0.3” more narrow than the MC250, and its width is almost half an inch shorter.

MIL-R-18546/1G has been superseded by MIL-PRF-39009/1D for modern equivalent resistors. In case of adding modern equivalent resistors, be sure to use RER70 resistors as they are dimensionally equivalent to the older RE70G and are 20W power resistors. There are aesthetic differences between the old style and modern style. Most notably is the change in heat sink design. Older MIL-R-18546 resistors have fins on the top of the casing and their Mil-Spec and manufacturer stamp are on the side. Newer, MIL-PRF-39009 resistors have eschewed the top style heat sink and moved the fins to the sides, allowing the Mil-Spec and manufacturer stamp to be visible on top of the resistor.

http://www.landandmaritime.dla.mil/programs/milspec/ListDocs.aspx?BasicDoc=MIL-PRF-39009

http://www.landandmaritime.dla.mil/programs/milspec/ListDocs.aspx?BasicDoc=MIL-PRF-18546