Onkyo TX-4500MKII (1979–1980)
A quartz-locked stereo receiver that brought broadcast precision and modular flexibility to the heart of the 1970s hi-fi stack
Overview
At 15.5 kg, the Onkyo TX-4500MKII lands in the rack with the heft of something built to last—no lightweight tuner this, but a full-function stereo receiver that doubles as a standalone preamplifier and high-performance FM section. Marketed as a "Quartz-Locked Stereo Receiver," it emerged during a period when Onkyo was refining its analog engineering to meet audiophiles’ demands for tuning accuracy and signal purity. Though often mistaken for a simple tuner, the TX-4500MKII is better understood as a hybrid: a receiver with the soul of a modular component system, allowing users to bypass its internal amplifier and use the preamp and tuner sections independently. This flexibility appealed to purists who already owned a high-current power amp or wanted to build a system piece by piece. Standing at 583 mm wide, 163 mm tall, and 430 mm deep, its substantial footprint fills a standard rack bay with authority, while the heavy steel chassis underneath resists vibration and contributes to long-term stability.
Key Features
Quartz-Locked FM Tuner with Double-Conversion Design
The TX-4500MKII’s most celebrated feature is its quartz-locked FM tuning system—a technology Onkyo pioneered and refined across generations. Unlike standard variable-capacitor tuners that could drift with temperature or age, this system used a quartz crystal reference to lock onto stations with exceptional stability. The double-conversion superheterodyne architecture minimized image frequency interference and improved selectivity, especially in urban environments where adjacent stations bled into one another. A high-gain RF amplifier boosted weak signals, while a precision-lapped tuning capacitor ensured smooth, accurate dial tracking. The illuminated analog dial, backlit in soft blue, kept tuning visible in dim environments and gave the front panel a distinctive glow. Functions were arranged in grouped controls under a crystal-clear solid plate glass cover, protecting switches while keeping them accessible—a design noted in contemporary reviews for its clarity and usability. High Fidelity (June 1978, p.101) described the layout as having "functions [that] are more prominent and in full view at all times, protected by crystal-clear solid plate glass."
Discrete Transistor Preamplifier Section
Beyond its tuner prowess, the TX-4500MKII housed a full preamplifier stage built around discrete transistor circuitry—no ICs in the signal path—engineered for low noise and high transparency. This allowed it to function as a standalone preamp when paired with an external power amplifier, a rarity in receivers of this class. The tone controls were musical rather than surgical, offering ±10 dB adjustment at 100 Hz and 10 kHz, with a "Twin Turbo" option providing ±15 dB at 50 Hz and ±6 dB at 10 kHz for more aggressive shaping. A full tape loop with monitor switching enabled recording from any source while listening to another, a crucial feature in the era of cassette dubbing and reel-to-reel archiving.
High-Power Output Stage
While exact impedance-specific power ratings are not confirmed in available documentation, sources suggest the amplifier section delivers approximately 60 watts per channel, with one listing citing a total RMS power rating of 120W—potentially indicating 60W per channel into 8 ohms. Whether that figure was achieved under full bandwidth or dynamic conditions remains unclear, and owners report occasional struggles to reach rated output, possibly due to aging power supplies or component drift. Gold-plated RCA jacks and high-quality potentiometers ensured clean signal transfer, while the robust internal layout supported stable operation under continuous load.
Historical Context
Introduced in 1979 and produced through 1980, the TX-4500MKII arrived at a time when integrated receivers dominated the mid-to-high-end market, combining tuner, preamp, and power amp in one chassis. Onkyo positioned the model as a mid-range offering, balancing advanced tuning technology with modular versatility. It followed the original TX-4500 and represented Onkyo’s second-generation quartz-locked design, improving on the first with refined ergonomics and enhanced circuitry. Audio (January 1979, p.89) referred to it as "the finest" in its class, noting that "Onkyo's innovative genius was improving on the first to produce the finest." Despite its technical merits, the TX-4500MKII never achieved the same name recognition as contemporaries like the Yamaha TU-3000 or Sony ST-555ES, remaining a cult favorite rather than a mainstream icon.
Collectibility & Value
Well-maintained units in working condition typically sell for $250–$400, with fully restored examples commanding higher prices—up to $599 for units described as having "very nice sound." Units listed as "AS-IS" or for parts have sold for around $430, reflecting demand even for non-functional units, likely due to their serviceable chassis and sought-after faceplates. Owners note a growing cult following among vintage tuner enthusiasts, with one Facebook poster calling it "a nice pice of history." Common issues include dried-up electrolytic capacitors in the power supply and audio coupling paths, which can cause hum or distortion if not replaced. The volume and tone controls often develop crackling due to dust or wear, though contact cleaner may help. The large tuning capacitor may stiffen over time and benefit from specialized lubricant—never general-purpose oil. A recurring hardware failure involves resistor R616 on the power amp board, which has been reported as burned in multiple user posts, often linked to transistor Q607. Some owners have also reported difficulty sourcing spare faceplates, indicating parts scarcity for cosmetic restoration.
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