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

In the mid-1980s, FM radio was still a primary source of high-fidelity music for home listeners. Onkyo had a reputation for building some of the most refined and technically advanced tuners on the market. One of its standout models from this period was the Onkyo TX-8500MKII, a stereo FM tuner that represented the pinnacle of analog broadcast reception technology. It isn't discussed as widely today as some of Onkyo's receivers or amplifiers. Vintage audio enthusiasts and FM purists still seek it out for its precision engineering, clean sound and elegant design.

Released in 1985, the TX-8500MKII was part of Onkyo's high-end tuner lineup, made to pair with separates systems of the era. It may have followed the original TX-8500 and incorporated several refinements, which would possibly explain the "MKII" designation. The result was a more stable, accurate and sonically transparent receiver of FM broadcasts. Many manufacturers were starting to shift focus toward digital audio and early CD technology at the time. Onkyo stayed with analog.

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	approximately 87.5–108 MHz
Tuning Steps	50 kHz
IF Frequencies	10.7 MHz (1st), 450 kHz (2nd)
Sensitivity (Mono)	2.8 µV for 30 dB SNR
Sensitivity (Stereo)	2.5 µV for 30 dB SNR
Signal-to-Noise Ratio	70 dB (weighted)
Total Harmonic Distortion	typically rated at <0.5%
Channel Separation	50 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	330 watts
Dimensions (W×H×D)	approximately 435 × 138 × 322 mm
Weight	24.9 kg (55 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. Seven 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 wanted faithful reproduction of broadcast content. Its dual-conversion IF system and high-quality S-meter let it pull in weak or distant stations 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. Stereo imaging was precise, with a wide soundstage. Live classical and jazz programs on FM came across 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, which points to good internal shielding and circuit layout. That made it suited to casual listening, and also to critical monitoring and archival recording of FM content.

Notable Features and Innovations

The TX-8500MKII may look modest next to today's digital streamers, but 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 had Onkyo's attention to mechanical detail: smooth rotary knobs, a satisfying button click, and a front panel layout that balanced function with looks. The brushed aluminum faceplate and blue-lit display gave it a 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 best performance, pair the TX-8500MKII with a high-quality outdoor FM antenna, such as a folded dipole or directional Yagi. 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.

Several factors drive its collectibility: Onkyo's reputation for build quality, the tuner's advanced feature set for the era, and growing interest in analog radio among audiophiles and retro-tech enthusiasts. It isn't a "blue chip" vintage tuner like the Sony ST-555ES. It 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 came from a time when FM radio was a legitimate high-fidelity medium. It reflects Onkyo's focus on detail, signal integrity and user-friendly design.

Though overshadowed by the rise of digital audio, the TX-8500MKII is still a good choice for anyone building a vintage separates system. It suits those who still listen to live broadcasts, classical music stations, or local jazz programs.

The Onkyo TX-8500MKII picks up its music from the airwaves, not from a file.

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