The MI-75 was an industrial version of the MC-75 with identical specifications, the main difference being finish and appearance. Heavier and larger than the MC-75 and sporting a rugged, grey hammertone chassis, the MI-75 had output voltages of 25, 70.7, 115 and 230V and output impedances of 4, 8, 16, 67, 150 and 600 ohms (all isolated from ground). All of the output impedance and voltage connections were supplied at the octal socket or on barrier strips.

Intended for rack mounting, the front panel was mounted underneath the chassis and contained a gain control, power switch, fuse and serious-looking red pilot light. Some versions have the same black transformers that were probably surplus parts from the MC-75 production. (see pictures at right).

Originally priced at $275 (around $50 more than its commercial counterpart), today the MI-75 is valued at around the same price as the MC-75, an original, matched pair (consecutive or very close serial numbers) fetches at least $2,500.

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