RCA MI-4856 Lateral Pickup Head
A single-purpose transducer that broadcast engineers once swapped like ground wire, and that survives today only in the classifieds of old trade papers. Audio (December 1947, p.42) noted Joseph P. Maxfield's move into consultant work. Maxfield did pioneering research in sound transmission and recording, and he shaped the era in which the MI-4856 was deployed.
Overview
The RCA MI-4856 was a lateral pickup head. It was the electromechanical cartridge at the business end of a broadcast turntable's tonearm, the part that traced the groove and turned the wiggle into voltage. In the mid-1940s it sat alongside the Western Electric D93306 vertical reproducer as one of the two standard front ends on a broadcast-grade playback setup. That is how it turns up in the surviving record: a South Carolina station advertising two Western Electric 2A turntables "each equipped with WE D 93306 vertical reproducers and RCA MI 4856 lateral reproducers," sold only as a unit for $400 FOB. So the MI-4856 was not a standalone accessory. It was half of a two-head arrangement, one head for lateral-cut discs and one for vertical, mounted on the same arm and switched as the transcription required.
The head was a serviceable, replaceable item rather than a permanent fixture. Broadcasters ran recurring "Wanted to Buy" notices through 1947 asking for "any quantity RCA Mi-4856 pickup heads." A 1944 notice offered to buy or swap "equal value in copper ground wire" for a single MI-4856 head, with or without the arm. Stations were bartering copper for them and buying them by the quantity rather than the each. That points to a consumable in a working plant, the kind of thing that wore out, got replaced, and got hoarded.
The MI-4856 was not a consumer product, at least on the evidence. It lived in radio stations, in the transcription racks, on the turntables that fed a transmitter. The prices in the period classifieds show it: a 1946 listing from WINX in Washington offered "2 RCA MI-4856 pickup heads, arms, and filters" at $90.00 each, and "3 RCA MI-4856 pickup heads only" at $30.00 each. The head alone was thirty dollars, and the complete assembly with arm and equalization filter was three times that. The filter was needed because lateral and vertical discs required different equalization, and a broadcast installation needed the matching network to play them back correctly. A loose MI-4856 head today is one-third of a system.
The classified columns that document it - the 1944 swap offer, the 1945 and 1946 for-sale listings, the repeated 1947 want-ads - bracket perhaps five years of active demand, after which the technology it served was displaced.
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