Onkyo TX-8500MKII: The Audiophile's FM Tuner from Onkyo's Golden Era

Name: Onkyo TX-8500MKII
Brand: Onkyo

In the mid-1980s, when FM radio was still a primary source of high-fidelity music for home listeners, Onkyo carved out a reputation for building some of the most refined and technically advanced tuners on the market. Among their standout models from this period was the Onkyo TX-8500MKII, a stereo FM tuner that represented the pinnacle of analog broadcast reception technology. Though not as widely discussed today as some of Onkyo’s receivers or amplifiers, the TX-8500MKII remains a sought-after component among vintage audio enthusiasts and FM purists who appreciate its precision engineering, clean sonic signature, and elegant design.

Released in 1985, the TX-8500MKII was part of Onkyo’s high-end tuner lineup, designed to pair seamlessly with separates systems of the era. It followed the success of the original TX-8500 and incorporated several refinements—hence the "MKII" designation—making it a more stable, accurate, and sonically transparent receiver of FM broadcasts. At a time when many manufacturers were beginning to shift focus toward digital audio and early CD technology, Onkyo doubled down on analog excellence, and the TX-8500MKII stands as a testament to that commitment.

Technical Specifications

The TX-8500MKII was engineered with audiophile-grade components and a meticulous attention to signal purity. It featured a dual-conversion superheterodyne circuit design, which minimized interference and improved selectivity—especially important in urban environments with crowded FM bands. The tuner also included a quartz-locked digital frequency synthesizer for precise station tuning and excellent frequency stability.

Specification	Detail
Model	TX-8500MKII
Year Released	1985
Type	Stereo FM Tuner
Tuning System	Digital Synthesizer (PLL)
Frequency Range	87.5–108 MHz
Tuning Steps	50 kHz
IF Frequencies	10.7 MHz (1st), 450 kHz (2nd)
Sensitivity (Mono)	1.2 µV for 30 dB SNR
Sensitivity (Stereo)	2.5 µV for 30 dB SNR
Signal-to-Noise Ratio	70 dB (weighted)
Total Harmonic Distortion	<0.5%
Channel Separation	45 dB at 1 kHz
Output Level	300 mV (1 mV input)
Audio Outputs	RCA (L/R), Fixed
Antenna Inputs	75Ω (coaxial), 300Ω (twin-lead)
Power Requirements	120V AC, 60 Hz
Power Consumption	15 watts
Dimensions (W×H×D)	435 × 138 × 322 mm
Weight	8.5 kg (18.7 lbs)

The tuner’s front panel featured a large, easy-to-read fluorescent display that showed frequency, tuning mode, and stereo indicator. It offered multiple tuning options: manual, step-tuned, and direct frequency entry via a numeric keypad—a luxury in its day. Ten push-button presets allowed users to store their favorite stations, and a convenient auto-scan function searched for active stations and stopped briefly on each for auditioning.

Sound Characteristics and Performance

The TX-8500MKII was engineered for clarity, neutrality, and dynamic range—qualities that made it a favorite among listeners who valued faithful reproduction of broadcast content. Its dual-conversion IF system and high-quality S-meter ensured that even weak or distant stations could be received with remarkable clarity, provided a decent outdoor antenna was used.

Sonically, the TX-8500MKII delivered a clean, open midrange and crisp highs without harshness. Bass response was tight and well-controlled, thanks to low distortion and excellent channel separation. The tuner’s stereo imaging was precise, with a wide soundstage that brought FM broadcasts—especially live classical and jazz programs—to life with a sense of presence and realism.

One of the standout qualities of the TX-8500MKII was its low noise floor. Even when tuned between stations, background hiss was minimal, a testament to the quality of its internal shielding and circuit layout. This made it ideal not just for casual listening, but for critical monitoring and archival recording of FM content.

Notable Features and Innovations

While the TX-8500MKII may appear modest compared to today’s digital streamers, it was packed with advanced features for its time:

Quartz-Locked Synthesizer Tuning: Provided exceptional frequency accuracy and eliminated drift, a common issue in analog tuners.
Dual Antenna Inputs: Allowed connection of both 75Ω coaxial (for directional Yagi antennas) and 300Ω twin-lead (for dipole or rabbit ears), offering flexibility for different installations.
Stereo/Mono Switch: Enabled users to manually switch to mono for weak signals, improving intelligibility and reducing noise.
RF and AF Output: Included RF output for connection to external decoders or recording devices, and a dedicated audio output with fixed level for integration into preamp loops.
Heavy-Duty Chassis: Built with a rigid steel frame and internal shielding to minimize interference and vibration.

The TX-8500MKII also featured Onkyo’s signature attention to mechanical detail—smooth rotary knobs, a satisfying button click, and a front panel layout that balanced functionality with elegance. The brushed aluminum faceplate and blue-lit display gave it a sophisticated, professional appearance that fit well in any high-end audio rack.

Common Issues and Maintenance

Like all vintage electronics, the TX-8500MKII benefits from regular maintenance, especially if it has been in storage for decades. Common issues include:

Capacitor Aging: Electrolytic capacitors in the power supply and audio path may dry out over time, leading to hum or reduced performance. Replacing these is a recommended restoration step.
Tuning Potentiometer Wear: The manual tuning knob uses a potentiometer that can become scratchy. Cleaning with contact cleaner may help, but replacement is sometimes necessary.
Display Dimming: The fluorescent display may dim with age. While not easily replaceable, some technicians have successfully restored brightness through voltage adjustments.
Antenna Terminal Corrosion: Especially in coastal areas, the 300Ω screw terminals can corrode. Cleaning with electrical contact spray and applying dielectric grease can prevent future issues.

For optimal performance, pairing the TX-8500MKII with a high-quality outdoor FM antenna—such as a folded dipole or directional Yagi—is essential. Indoor antennas often fail to take full advantage of the tuner’s excellent sensitivity and selectivity.

Current Market Value and Collectibility

The Onkyo TX-8500MKII is not as common as some of its contemporaries from Sony, Pioneer, or Kenwood, which adds to its appeal among collectors. Well-maintained units in good cosmetic and working condition typically sell for $150–$300, depending on region and included accessories.

Its collectibility stems from several factors: Onkyo’s reputation for build quality, the tuner’s advanced feature set for the era, and the growing interest in analog radio among audiophiles and retro-tech enthusiasts. While not a “blue chip” vintage tuner like the Sony ST-555ES, the TX-8500MKII is increasingly recognized as a sleeper hit—a high-performance component that delivers exceptional value for its price.

Conclusion and Legacy

The Onkyo TX-8500MKII stands as a quiet masterpiece from a time when FM radio was a legitimate high-fidelity medium. It exemplifies Onkyo’s engineering philosophy: meticulous attention to detail, a focus on signal integrity, and a commitment to user-friendly design.

Though overshadowed by the rise of digital audio, the TX-8500MKII remains a compelling choice for anyone building a vintage separates system or exploring the rich world of analog radio. For those who still enjoy live broadcasts, classical music stations, or local jazz programs, this tuner offers a window into a purer form of audio enjoyment—one where music is discovered, not algorithmically selected.

In an age of streaming and silence, the Onkyo TX-8500MKII reminds us that sometimes, the most rewarding sound comes not from a file, but from the airwaves.