1955 RCA 7BT-9J
Micro-table radio, thermoplastic cabinet with aluminum face
5 1/2 x 3 1/4 x 1 1/2 inches / 140 x 82.5 x 38 mm
Six transistors (Texas Instruments, RCA: 2x TI234, TI235, 3x 2N109), superheterodyne circuit
One tubular 9-volt battery
RCA's first transistor radio (possibly second?), released in October 1955 at about the same time as the 7BT-10K lunchbox radio.
A relatively low-production radio for whatever reasons — all of the examples I've seen on eBay auctions or transistor radio web pages over the past twenty years that displayed serial numbers have shown numbers under 20,000, most of them under 10,000 — the serial number on this example, for instance, is 4585.
I was lucky enough to find this RCA complete with its shipping box, all papers, and a gray flannel carrying pouch — I've added a photo toward the bottom of this page showing some of the ephemera.
Like many radio manufacturers, RCA produced several prototypes before releasing its first commercial transistor radio: the 1952 prototype, a radio which found its way onto eBay several years ago and sold for massive bucks, and apparently also a 1953 prototype, as reported in a December 15, 1953 article in the New York Times.