The 101J is a PCB-mount miniature audio transformer encased in rugged black epoxy, designed to withstand severe environmental conditions, including those specified by MIL-T-27 (grade 5, class S). It features pin-type connections for easy mounting on a printed circuit board, bifilar winding technique for reliable signal transfer, and allows the secondary and primary windings to be interchanged. The transformer is rated for a power level of 100mW across a frequency range of 300Hz to 100kHz, making it suitable for audio applications.