Sony ST-A6B (1977-1980)
A high-performance FM/AM stereo tuner with PLL synthesis and 7-gang varicap tuning, designed for balanced reception and audio quality.
Overview
The Sony ST-A6B is an FM/AM stereo tuner made by Sony Corporation in Tokyo, released in 1977 and produced through 1980. It was developed to balance strong reception performance, audio fidelity, and user-friendly operation. Designed as a more affordable alternative to the ST-A7B, the ST-A6B shares core technology with its higher-end sibling while offering solid performance that holds up against many mid-tier 'super' tuners of its era. Though overlooked at the time, it has gained recognition for its capable engineering and build.
Specifications
| Tuning range | 87.5 - 108 MHz |
| Practical/Usable sensitivity (FM) | 10.3 dBF (1.8 µV) |
| 50 dB quieting (mono) | 15.9 dBf (3.4 µV) |
| 50 dB quieting (stereo) | 37.1 dBf (39 µV) |
| Signal-to-noise ratio (FM) | 70 dB |
| Capture ratio | 1.5 dB |
| Selectivity (IHF) | Normal: 35 dB, Narrow: 80 dB |
| Alternate channel selectivity | 70 dB |
| AM suppression | 50 dB |
| Image rejection | 80 dB |
| IF rejection | 90 dB |
| Spurious response rejection | 90 dB |
| RF intermodulation | 80 dB |
| Subcarrier suppression | 70 dB |
| Distortion Factor/THD (FM) | 0.3% |
| THD (mono, normal) | 0.08% |
| THD (mono, narrow) | 0.2% |
| THD (stereo, normal) | 0.15% |
| THD (stereo, narrow) | 0.4% |
| IM Distortion (mono, normal) | 0.08% |
| IM Distortion (mono, narrow) | 0.2% |
| IM Distortion (stereo, normal) | 0.15% |
| IM Distortion (stereo, narrow) | 0.4% |
| Stereo separation (1kHz) | 35 dB |
| Frequency response (FM) | 30 - 15,000 Hz, +0.5 -1.5 dB |
| Fixed outputs | 650 mV, 2.2 kΩ |
| Variable output | 1.2 V max. / 200 Ohm |
| Power consumption | 18W |
| External dimensions | 430 x 145 x 335 mm |
| Weight | 8.5 kg |
| Power Requirements | AC 100, 120, 220, 240 V, 50/60 Hz |
| Usable Sensitivity (IHF): AM | 300 µV/m |
| Signal-to-Noise Ratio: AM | 45 dB |
| Total Harmonic Distortion: AM | 0.8% |
| Frequency Response: AM | 50 - 3,000 Hz |
Design
The ST-A6B uses a PLL (Phase Locked Loop) synthesizer system for precise tuning and features a Pulse Count Detector (PCD) system for FM detection. Its front-end includes a dual gate MOS-FET RF amplifier, a dual gate MOS-FET mixer, and a FET-buffered local oscillator, leveraging a 7-gang varicap and 4-gang variable capacitor. The tuner employs a quad loop tune circuit with a 7-row CG varicon and a quadruple-tuned antenna circuit. The IF stage uses a Sony Uni-Phase uniphase filter, and the MPX section uses a PLL IC. It includes a high-blend circuit, automatic switching between Normal and Narrow modes based on signal strength, and a muting circuit using a reed relay. Additional features include a built-in 400 Hz Cal Tone for setting recording levels, Low Cut and High Cut filters, a signal/multipath meter, and both fixed and variable audio outputs with an F-type 75 Ω coaxial antenna connector.
Context
The ST-A6B was likely intended as a more affordable alternative to the ST-A7B. It shares the same fundamental design with the Japan-only ST-A5, which features a similar 7-gang varicap and silver finish but was not sold outside Japan.
Market
The ST-A6B is fairly rare in the USA but remains quite abundant in Europe. There is no need to pay a premium for one, as many units are still available.
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