RCA MI-4875 Universal Pickup
One head, one ounce of pressure, and a diamond tip. It was the piece of RCA broadcast iron that let a station play any disc in the library without reaching for a second cartridge.
Overview
The MI-4875 is a phonograph pickup, not a turntable, but it is the most important part of the RCA transcription chain. Before it, playing a vertical-cut transcription and then a standard lateral commercial pressing meant two different heads, two alignments, and two chances to damage a disc. The MI-4875 tracked both. RCA's own advertising for the Type 70-C1 turntable that carried it made that the headline: lateral and vertical reproduction from the same head. For a station with a mixed library of transcriptions and conventional pressings, that was the whole argument in one line.
The numbers are the interesting part. RCA specified pickup response flat within ±2 db from 50 to 10,000 cycles, which in the late 1940s covered essentially everything a broadcast transcription was expected to deliver. The stylus was a diamond ground and polished to microscopic accuracy. In practice that meant no needle changing between plays and no sapphire to wear flat mid-shift. Tracking pressure was one ounce. That is not a typo for grams. It is a period specification, from an era when pickup design and disc formulations were built around each other.
The switching around the pickup is what made the MI-4875 more than a cartridge. RCA paired it with a six-position frequency-characteristic switch and a special filter unit - two vertical positions and four lateral positions - so the operator could select the playback curve that matched the disc in hand instead of compromising on a single fixed equalization. With a stack of 1940s transcriptions cut to different house curves, six positions was not overkill. It was the minimum.
The pickup was the head specified for the RCA Type 70-C1 transcription turntable, an update to the Series 70 line that RCA claimed had more than 2,000 units in service at the time of the announcement. The 70-C1 carried over the 70-C's speed regulation - rotation precise within 0.6 percent at 33 1/4 r.p.m. and within 0.4 percent at 78 r.p.m. - and its low noise floor, and added the MI-4875 as the reason to buy. A Type 72-C Instantaneous Recording Attachment could be added to the same machine. Cabinets came finished in black or umber gray with chromium trim.
The MI-4875 also circulated on its own. It shows up in the broadcast trade press of the period as a standalone item - a pickup, arm, filter, and switch sold as a kit, listed in the classified columns of Broadcasting at $110 new, and sought by engineers at stations that wanted the RCA head on a non-RCA table. One 1947 listing offers two MI-4875-G universal pickups alongside a pair of QRK turntables, all new and never opened. That suggests the head was being bought to retrofit existing decks rather than only as part of a 70-C1 package. Two RCA Universal pickup kits, type MI 4875-C, were wanted to buy in a 1946 issue by an engineer at WHEB in Portsmouth, New Hampshire. The MI-4875 appears in the record as a -C and as a -G, and the documentation does not spell out what changed between them. Treat the suffixes as variants of the same head rather than assume a clean chronology.
Period coverage of the pickup itself is thin. RCA's advertising for the Type 70-D in Audio (December 1947, p.40) leaned on the same "standard of the studios" line and the same "over 3000 units" claim for the Series 70 family, but the MI-4875's own moment in print is mostly the announcement copy and the classifieds. What the trade listings do establish is price and availability: $110 for a new pickup, arm, filter, and switch in 1946, against $100 for a used Western Electric 9A vertical/lateral setup offered in the same column. RCA was not the cheap option.
For a collector today, the MI-4875 is a specialist's piece. It is not a hi-fi cartridge and was never sold as one. It is broadcast iron, designed to survive a station's operating schedule and to be serviced rather than replaced. Complete examples with the arm, filter, and six-position switch intact are considerably more useful than a bare head, because the switching is half the design. The diamond stylus is the failure point, and a worn or chipped tip on an original is not a cosmetic issue on a pickup that tracked at one ounce. Check the stylus before anything else.
The MI-4875 solved a specific problem: how to play every disc in a 1940s station library without owning every head. It was specified into RCA's own turntables and bought separately by engineers who wanted it on somebody else's.
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