Sony STR-6500 (1970s)

At 7.25 kg, it carries the weight of early 1970s engineering ambition. It is dense, deliberate, and built for stereo broadcasts.

Overview

The Sony STR-6500 is not a showpiece. It has no flamboyant power and no oversized dials. It is an FM/AM stereo receiver from the early 1970s, built to bring the high-fidelity performance of Sony's ES series to a broader audience. It cost ¥44,800 around 1970, which put it in the mid-tier: serious enough for audiophiles, affordable enough for enthusiasts moving up from console systems. The rated output is 15W + 15W (8 Ω). That won't shake walls, but with efficient speakers it gives a clean, controlled sound with low distortion and solid tuner performance. It is not a brute-force amplifier. The tuner section punches well above its class.

The tuner is what stands out first. It covers 76 MHz to 90 MHz, with a 70 dB signal-to-noise ratio and 40 dB or more stereo separation at 400 Hz. Those figures rival far more expensive units. The front end uses a direct mixer system with a 4-row precision varicon and a newly developed low-noise FET. That keeps cross-modulation distortion down and avoids active devices in the high-frequency path. Six-element solid-state filtering gives 70 dB of selectivity (IHF), so adjacent-channel interference is held in check. For AM, a ferrite bar antenna and an external terminal feed a stage with a FET and a double-tuned ceramic filter to suppress noise and interference, with 45 dB image rejection at 1400 kHz. Sony did not cut corners on this section.

Specifications

Manufacturer	Sony
Product Type	FM/AM stereo receiver
Receiving Frequency (FM)	76 MHz to 90 MHz
Practical Sensitivity (FM)	2.0 μV ± 1 dB (IHF)
Signal-to-Noise Ratio (FM)	70 dB
Capture Ratio	2.0 dB
Selectivity	70 dB (IHF)
FM Stereo Separation	40 dB or more (400 Hz)
Receiving Frequency (AM)	530 kHz to 1,605 kHz
Dynamic Power	44W (8 Ω, both channels operating)
Rated Output	15W + 15W (8 Ω); 13W + 13W (16 Ω)
Harmonic Distortion Factor (1 kHz)	0.5% or less (Rated Output); 0.1% or less (at 0.5W Output)
Frequency Characteristic (Aux, Tape, Rec/PB)	20 Hz ~ 60 kHz +0 -3dB
S/N Ratio (Phono)	70 dB or more (input 3 mV)
Input Sensitivity / Impedance (Phono)	2.5 mV / 47 kΩ
Input Sensitivity / Impedance (Aux1, 2, Tape)	250 mV / 100 kΩ
Speaker Output Impedance	4 Ω ~ 16 Ω
Power	100 VAC, 50 Hz / 60 Hz
Power Consumption	Maximum power: 80W; No signal: 20W
External Dimensions	Width 400 x Height 145 x Depth 310 mm
Weight	7.25 kg

Key Features

Direct Mixer System with Low-Noise FET

The STR-6500's FM tuner avoids active devices in the high-frequency path by using a direct mixer system. Radio waves go straight into the mixing stage through three tuning circuits, which the newly developed low-noise FET makes possible. This reduces cross-modulation distortion, which is common in crowded bands, and helps the tuner reach a 2.0 dB capture ratio and 75 dB image rejection.

6-Element Solid-State Filter for Selectivity

A solid-state filter made of six elements gives 70 dB of selectivity (IHF). That keeps reception clean even in electrically noisy environments.

Front-Panel Aux Input with Quick Access Switch

Special High Filter with High Blend Function

High-frequency noise can get intrusive on weak FM stereo signals. The STR-6500 has a dedicated high filter (5 kHz or more, 6 dB/oct) that reduces it. It also has a high blend function, which sums the high-frequency content of the left and right channels. That keeps the stereo image stable while cutting hiss, and it helps on marginal reception.

Monitor Switch for 3-Head Tape Recording

Green Dial Illumination and Tuning Meter

The FM equally spaced scale dial is illuminated in green, a Sony touch of the era. A dedicated tuning meter gives peak indication for both AM and FM. There are no flashing lights or gimmicks.

Silicon Transistors in Amplifier Section

The amplifier uses silicon transistors to keep distortion down. Harmonic distortion is 0.5% or less at rated output (1 kHz). At lower levels (0.5W) it drops to 0.1% or less. The 15W + 15W output is modest by modern standards, but the damping factor of 25 (8 Ω) suggests tight control over speaker cones, especially with compatible loads.

Historical Context

The STR-6500 was designed as a bridge—bringing the high-performance DNA of Sony’s ES series to a wider audience. It arrived during a pivotal moment in Japanese audio, when integrated receivers were evolving from basic AM/FM units into serious high-fidelity components. While not a flagship, it carried flagship-level engineering in its tuner design. Today, it’s recognized as a “Classic Model” by Sony, a nod to its role in democratizing quality audio during the early 1970s.

Collectibility & Value

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