[Doug Houston]

I don't know if this is the sme one i wrote some comments on in the antique radio board. But anyway, RCA is my other passion in radios, and the C15 sets fall right into the arena of preference for me. The model year was 1936, and it was the first year for metal tubes, and also the first year for tuning eye tubes. Among my collection is a C13-2, almost a C-15! The next year, 1937, had the 15k, the counterpart of the C15. In those years, the big technology race was between RCA and Philco. Zenith was a follower, but never a contender in the technology contest. Also, the 1936-37 years were the plateau of achievement for performance in radio. The next step upward came in the late thirties, with the introduction of hotter tube types for television applications, and also the loktal tube line by Sylvania. The new design innovation of the Loktals made possible better performance at high frequencies than the earlier tubes could deliver.

The initial menu of metal tubes consisted of nine types, developed by GE, and manufactured by RCA. The big advances from metal tubes were self-shielding, the octal base, and two new types, which were unlike anything previously. They were 6L7 and 6H6. The performance of metal tubes at high frequencies was marginally better than that of the fat pin tubes, if at all. In the 1936 model RCA's, tuning was set up to cover up to around 60 megacycles, and some RCA sets would get up that far, but not all of them. i have several of those models, and if they do work up that high, they will pick up channel 2 video and sound. The 6K7 in the RF stage is the determining factor.

Since RCA was in the record business, they made some very superlative record players. their 1936 line includeed the model D22-1, a phonograph combination, with a 22 tube count. The 6L7 and 6H6 made possible a volume expander for the phonograph, giving it an expanded dynamic range. The power output of the set was around 30 watts, with push-pull prallel 2A3 power amps, driving two 12 inch speakers. An example of that creation is also in my collection, and lives up to the expectations that its specs suggest. The radio receiver circuitry is the C13 design.