Pioneer TX-9500 II
Pioneer's answer to the selectivity-versus-fidelity tradeoff: a tuner with two complete IF chains and a front end built around three MOS-FETs.
Overview
The TX-9500 II is an AM/FM stereo tuner that U.S. Pioneer Electronics positioned as the successor to its TX-9500 — a set that Popular Electronics, in Pioneer's own retelling, had called about as "near to perfect" as it had encountered. The II was the company's attempt to push past that. As Pioneer's 1977 advertising put it, the new model packed technology so fresh that some of it hadn't been perfected until that year. Advertising copy is not a verdict, but the engineering underneath it is genuinely unusual for a tuner at this price.
The headline is the front end: three newly developed MOS-FETs working alongside a five-gang variable capacitor, which together give the TX-9500 II an FM usable sensitivity of 8.8 dBf in mono (1.5 µV). In practical terms that means pulling in clean FM far from the transmitter — the spec sheet's numbers, not marketing, tell that story. The circuit description confirms two dual-gate MOS-FETs as RF amplifiers, a third MOS-FET as the mixer, and a buffer stage after the local oscillator.
What separates the II from most tuners of its era is the selectable IF bandwidth. Rather than switching one or two circuit elements as most designs do, the TX-9500 II runs two complete IF systems: a wide-band path built around a surface acoustic wave filter plus a four-pole phase-linear filter, and a narrow-band path using a 10-element ceramic filter for high alternate-channel selectivity. The wide mode is for strong local stations; the narrow mode scrubs interference and noise off weak ones. Measured distortion at 1 kHz in stereo runs an incredibly low 0.07% in wide and 0.25% in narrow — both below the threshold of human hearing, per Pioneer's own figures.
The multiplex section is a phase-lock-loop design with automatic pilot-carrier cancellation, which lets the tuner deliver extended flat frequency response in stereo without paying for it with carrier leakage at the output. A separate audio and MPX muting assembly uses three special-purpose ICs, one handling audio amplification and isolation with full negative feedback in a differential direct-coupled circuit. The total semiconductor complement is substantial: five FETs, 15 ICs, 12 transistors, and 19 diodes. The power supply delivers two fully regulated voltages for the critical FM and AM circuits.
Around back, the tuner carries the expected external AM, ground, and 300-/75-ohm antenna terminals, with a clamp to retain coaxial cable. There are fixed and variable output jacks, horizontal and vertical scope outputs for visual multipath observation, and an unswitched a.c. convenience receptacle. A pivotable ferrite bar serves as the built-in AM antenna. A slide switch locked in its 75-microsecond de-emphasis position can be moved to 25 microseconds by removing a retaining bracket — the provision for Dolby FM reception with an outboard decoder.
The front panel follows Pioneer's house styling of the period: an all-gold face, a dial area that slopes back for easy viewing, signal-strength and center-of-channel meters at mid-scale above the FM and AM dial scales. A stereo indicator lights to the right of the meters; two rectangles at the left show wide or narrow IF selection. Four movable markers glide along the lower dial edge — Pioneer's "memory markers" — for flagging the frequencies most often tuned. Controls include a toggle power switch, the wide/narrow IF switch, a three-position multipath check switch, a 440-Hz calibrating tone at 50% modulation for presetting tape record levels, a rotary output-level control, a three-position muting control (off plus two thresholds), the large tuning knob, and a function selector with AM, FM, FM with noise filtering, and FM-mono positions. The noise-filter position is intended for weak-signal stereo and reduces high-frequency separation without altering overall frequency response.
According to Audio (May 1977, p.69), Pioneer had joined the small group of FM tuner designers who accepted that the medium is full of compromises — super selectivity traditionally came at the cost of super-low distortion and super-high separation — and the TX-9500 II's selectable bandwidth was the attempt to give listeners the best of both worlds. The same review noted that while such switching had been available on high-end tuners from Yamaha, Sansui, and McIntosh for some years, the accomplishment was all the more remarkable given this tuner's price. Audio (May 1977, p.70) measured the TX-9500 II as effectively two tuners in one, repeating each of the many measurements for both bandwidth settings.
Those lab results are worth lingering on. In mono, ultimate signal-to-noise for strong signals was the same 80 dB in both modes — probably the limit of the test equipment — but the narrow mode quieted more steeply at low input levels, reaching 50-dB quieting at 2.0 µV (11.2 dBf) versus 2.2 µV (12.0 dBf) in wide. Best distortion readings were 0.03% in wide and 0.06% in narrow. Selectivity measured 86 dB in narrow against 35 dB in wide. In stereo the wide position held distortion to 0.06% at 1 kHz — about the lowest the reviewers had ever read for a tuner in stereo — while the narrow position rose to around 0.22% under the same conditions. Usable stereo sensitivity measured 6.0 µV (20.8 dBf) in either mode, and mono sensitivity measured exactly 1.5 µV (8.7 dBf). Separation peaked near 50 dB at mid frequencies in wide, falling to 40 dB at 50 Hz and 38 dB at 10 kHz; narrow held a superb 45 dB at mid frequencies, 38 dB at 50 Hz, and 32 dB at 10 kHz.
The manufacturer's own published figures are equally specific: 50-dB quieting sensitivity of 13.2 dBf (2.5 µV) mono and 36.1 dBf (35 µV) stereo; S/N of 82 dB mono and 77 dB stereo; frequency response of 20 Hz to 15 kHz, +0.2/−0.5 dB; AM suppression 65 dB; image rejection 120 dB; IF rejection 105 dB; spurious rejection 110 dB; capture ratio 0.8 dB wide and 2.0 dB narrow; selectivity 35 dB wide and 85 dB narrow. The AM section is no afterthought either — 15 µV external-antenna sensitivity, 30 dB selectivity, 55 dB S/N, 70 dB image rejection, and 65 dB IF rejection.
Physically the tuner measures 16 9/16 inches wide, 5 7/8 inches high, and 15 9/16 inches deep, and weighs 20 lbs. 15 oz. (9.5 kg) — a substantial chunk of metal for a tuner, which is part of why these survive so well. Output level is 650 mV fixed or 50 mV to 1.3 V variable on FM at 100% modulation; 200 mV fixed or 15 mV to 400 mV variable on AM at 30% modulation.
Collectors chasing the TX-9500 II are chasing a specific thing: a tuner that behaves like two, with the wide mode for fidelity and the narrow mode for pulling a weak station out of a crowded dial. It is the sort of piece that rewards a decent antenna and a little patience with the multipath switch. The gold face and sloping dial make it a natural match for the SA-9500 II integrated amplifier it was introduced alongside, and the two are frequently sought as a set. Prices and current market activity vary; buyers should confirm condition and that both IF modes are functioning, since the dual-chain design is the whole point of the model.
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