Sansui TU-555 (1968)
A solid-state FM/AM tuner released in June 1968 with advanced drift compensation and a pure electronic stereo switching system.
Overview
The Sansui TU-555 is an FM/AM tuner produced in June 1968, featuring a 3-gang FM tuning capacitor and FET-based RF stage for improved reception. It delivers strong performance with low distortion and high selectivity across both FM and AM bands. Designed for high-fidelity use, it includes a stereo indicator, muting switch, and a large tuning meter for precise station alignment. The unit was praised for its excellent FM sound and reception quality, described as "a real high-end product of its time."
Specifications
| Receiving frequency (FM) | 76 MHz to 90 MHz |
| Sensitivity (FM) | 2.5 μV (IHF) |
| Harmonic distortion factor (FM) | 0.8% or less |
| Signal-to-noise ratio (FM) | 60 dB or more |
| Selectivity (FM) | 45 dB or more |
| Capture Ratio (IHF) | 3.0 dB |
| Image ratio (FM) | 50 dB or more |
| IF Rejection (FM) | 60 dB or more |
| Spurious Radiation | 34 dB or less |
| Spurious response rejection | 60 dB or more |
| FM stereo / separation | 35 dB or more |
| Antenna input (FM) | 300 Ω balance; 75 Ω unbalance |
| Receiving frequency (AM) | 535 kHz to 1605 kHz |
| Sensitivity (AM, IHF) | 20 μV |
| Image ratio (AM) | 40 dB or More (1 MHz) |
| IF Rejection (AM) | 60 dB or More (1 MHz) |
| Selectivity (AM) | 20 dB or More |
| Output Level / Impedance | 1.5 V / 10k Ω or More |
| Power supply voltage | 100 VAC, 50Hz/60Hz |
| Power consumption | 10VA |
| External dimensions | 292 x 111 x 267 mm (W x H x D) |
| Weight | 3.9kg |
| Tuning Bands | FM, MW (AM) |
| Tuning Scale | Analogue |
Design
The TU-555 uses FET and a 3-row varicon in its FM/AM tuner design, with the FM front-end employing a 3-row varicon and FET in the RF stage. The AGC circuit enhances selectivity in strong electric fields, while a 4-stage IF amplifier and 3-stage limiter ensure strong signal handling. Power supplies for FM and AM sections are stabilized using zener diodes, and the design eliminates the need for an AFC circuit by compensating for temperature drift. The stereo decoder uses filter-hybrids like the FP-38A, and the unit features a pure electronic FM stereo/mono switch with automatic switching via FM-AUTO when broadcasts change from mono to stereo. It includes both short- and long-range FM antenna attenuators, a high-sensitivity ferrite bar for AM, and switchable output levels. The FM and AM front-ends were manufactured by Alps.
Market
Original pricing was ¥28,900 at release. Common issues include degraded electrolytic capacitors and awkward internal wiring, with repairs typically involving replacing all electrolytic caps and servicing the stereo decoder—such as replacing defective filter-hybrids. A separate wood case, model C-10, was available. Proper setup requires adjusting the FM-MPX separation on the back panel.
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