Harman Kardon HK503 (1979 / 1987–1989)
The Harman Kardon HK503 is a stereo receiver with conflicting production dates in the period record. One source places it in 1979, another in the 1987-1989 window. The archive has not yet resolved which is correct. The hardware is better documented: 50 watts per channel into 8 ohms, 60 watts into 4 ohms, and total harmonic distortion listed at 0.09%.
The surviving specs describe a well-equipped unit for its era. The HK503 has both MM and MC phono inputs (2.5 mV sensitivity each), plus high-level inputs for tuner, CD, and aux. It also has two tape loops with matching record outputs. A preamp output and two sets of speaker terminals round out the rear panel. Frequency range runs from 5 Hz to 100 kHz, and signal-to-noise ratio is rated at 88 dB. It measures 440 x 121 x 365 mm (W x H x D).
Inside, the parts count is 3 ICs, 14 FETs, 14 transistors, 62 diodes, and 4 zener diodes. HiFI-Stereo (September 1978, p.92) mentioned the HK503 alongside its sibling, the 60-watt HK505, in a roundup of new integrated amplifiers. No substantive review or measured performance data from that period has survived in the accessible record. No original price, weight, or tuner-section specifications are documented.
The HK503 is thinly documented in Harman Kardon's receiver lineup, and its exact place in the brand's history is still being sorted out.
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