Harman Kardon SR-600B (1966)
Eighty watts of IHF music power, a bandwidth that reaches 75,000 cycles, and germanium outputs that run cooler than silicon. This is the Stratophonic "B" Series receiver that Harman-Kardon advertised as the most complete FM stereo unit in its price class.
Overview
The SR-600B arrived in 1966 as part of what Harman-Kardon called its "B" Series of Stratophonic all-transistor stereo receivers. The company's advertising billed it as "the most complete FM stereo receiver in its price class." The numbers behind that claim are big: 80 watts IHF music power, a power bandwidth of 6 to 50,000 cps IHF, and a frequency response of 8 to 40,000 cps ±1 dB at full rated power. HiFI-Stereo (March 1966, p.41) ran the same "B" Series announcement. It described the line as delivering increased power, with a power bandwidth and flat response that held far beyond what comparable receivers managed at a single watt. Nobody strictly needed response to 40,000 cycles, but one contemporary write-up called Harman-Kardon "clearly a wide-frequency response advocate."
The engineering behind those numbers is the germanium output stage. Harman-Kardon's own advertising made a lot of the diffused-junction germanium transistors in all output circuits. It argued that germaniums increase bandwidth and reliability and run far cooler than any silicon output transistor then available. Collectors who have worked on these units note that germanium devices behave differently from later silicon, and that bias stability and thermal drift are their own discipline. The SR-600B also carried the Series' two-room stereo feature, which lets an owner hear stereo in one or two rooms, separately or simultaneously.
Tuning specs were respectable for the money. Usable FM sensitivity is rated at 1.95 microvolts IHF, and image rejection is quoted at better than 40 dB. Audio-Fan (June 1966, p.28) described the front panel as carrying "most any provisions you can think of," and singled out the contour switch, tape monitor, high and low frequency cutoffs, and tone-control in/out switching. Harmonic distortion is listed at less than 1%.
The price was $369, with an optional walnut enclosure at $29.95. Audio-Fan (June 1966, p.28) reported both figures directly. That put the SR-600B below its bigger sibling, the SR-900B, which carried 100 watts IHF music power, a 3 to 75,000 cps power bandwidth, 5 to 60,000 cps full-power response, distortion under 0.2%, and usable FM sensitivity of 1.85 microvolts, at $449. The line also included the AM/FM SR-400B at 60 watts for $309 and the FM-only SR-300B at $279, both sharing the SR-400B's specification set. The SR-600B was the middle of the range.
What the SR-600B represents today is a clean snapshot of the moment solid-state receivers displaced tubes in the American hi-fi market — Harman-Kardon's own copy leaned hard on the all-transistor story, and the "B" Series was the vehicle. It is a 1966 receiver with 1966 priorities: generous IHF power ratings, an aggressively wide claimed bandwidth, germanium outputs, and a front panel loaded with switching. Documentation for the model survives mainly through period advertising and the contemporary equipment roundups, which is worth knowing before hunting one down — service information is thinner than for the more heavily sold models, and the germanium output stage means repairs call for someone comfortable with that generation of transistor circuitry rather than a modern silicon-first bench.
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