RCA TP-15 Universal Multiplexer
This box doesn't make sound or pictures. It decides which of several projectors feeds the camera, and in 1955 that made it the hub of a film operation.
Overview
The RCA TP-15 is a broadcast television film multiplexer. It belongs to a corner of vintage gear that almost nobody collects: the plumbing between a projector and a camera. RCA's own house publication, RCA Broadcast News 84 (August 1955), called it "RCA's newest TP-15 Universal Multiplexer" and described it as the "hub" of a film system built for both color and monochrome. That is all that survives in the documented record - a handful of sentences from two issues of a trade paper. No spec sheet, no price, no dimensions.
Those sentences do say what the job was. The TP-15 was designed for use with 3-V color and 1-V monochrome film cameras, and with 16mm, 35mm and slide projectors in a variety of combinations for TV film pickup chains. In plain terms, a station had a camera pointed at a projector, and the TP-15 let that camera look at any one of several projectors without anyone physically moving anything. That is what "multiplexer" means here - an optical switchboard.
The "universal" in the name is the interesting part. According to RCA Broadcast News 93 (February 1957), using the TP-15, "color and monochrome film equipment can be completely integrated - by adding a TK-26 color" camera. The 1955 issue put it more grandly, describing the TP-15 as providing "the nucleous of an integrated 3-V and 1-V film camera system for both color and black-and-white films". The spelling is original. RCA's house magazine was not above a typo. The pitch was modularity: one multiplexer, one camera, and a station could build a film chain that handled color and black-and-white, film and slides, without duplicating the expensive part.
Key Features
Multi-Input Optical Switching for 16mm, 35mm and Slides
The core capability documented for the TP-15 is its accommodation of "16mm, 35mm and slide projectors in a variety of combinations for TV film pickup chains," per RCA Broadcast News 84 (August 1955). 16mm was the workhorse news and commercial film gauge, 35mm was the prestige and network gauge, and slides were the cheapest way to put a still image on air. A station that could route all three into one camera had a flexible film department. The TP-15 was sold as the mechanism that made that routing possible.
Color and Monochrome Integration via the TK-26
RCA's 1957 write-up in RCA Broadcast News 93 frames the TP-15 as the enabler of a fully integrated color and black-and-white film setup once a TK-26 color camera was added to the chain. The phrasing is careful. The multiplexer is the integration point, and the camera is the addition. For a station weighing the cost of color, that was the argument: the TP-15 you already owned did not become obsolete when you went color.
Positioned as the System Hub
Both source fragments use the same language of hubs and foundations. The 1955 issue calls the TP-15 "the hub ol this Film system for both color and monochrome" (OCR intact) and says it "provided the nucleous of an integrated 3-V and 1-V film camera system." This is marketing copy from RCA's own publication, not an independent verdict. It does show what the product was for: not a peripheral, but the piece everything else connected through.
Historical Context
The TP-15 enters the documented record in August 1955, when RCA Broadcast News 84 described it as RCA's newest universal multiplexer. By February 1957, RCA Broadcast News 93 was listing it alongside the TP-11B - "RCA TP-llB and TP-15 multiplexers provide excellent facilities for this multiplexing requirement" - grouping the two as comparable tools for the same job. The source gives no indication of which sat above the other in RCA's lineup. A surviving forum thread title pairing "RCA TP-15 Multiplexer vs TP-11" suggests owners have wondered about the same thing, though no content from that discussion was recoverable.
Production years, original price, and any technical specification remain undocumented. What can be said is narrow: the TP-15 existed by 1955, was still being referenced by RCA in 1957, and was built to multiplex multiple film and slide sources into color or monochrome television cameras. How the optics actually worked, what it weighed and what it cost have not surfaced in the available record.
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