Realistic QTA-790 (1973)
Radio Shack's big quadraphonic receiver, complete with a palm-sized wireless remote that physically turns the volume knob.
Overview
A four-channel receiver with a wireless remote is the kind of thing that sounds like a gimmick until you actually use it — and the QTA-790's remote is the least gimmicky part of the whole machine. It doesn't scan the dial; it selects among five stations you've already pre-set, and it nudges the volume up or down by way of a geared-down miniature motor physically coupled to the volume control shaft inside the receiver. Push the button and the knob turns. Audio (July 1973, p.42) walked through the arrangement in detail and came away calling it quite sufficient, noting the remote receiver module alone required 21 transistors. Radio Shack's own advertising, fronted by Boston Pops conductor Arthur Fiedler, billed the wireless remote as the headline feature — "pre-set your 6 favorite stations, control tuning and volume from your easy chair," as the copy ran in High Fidelity (July 1973, p.91). Marketing, sure. But the thing actually worked the way the copy said.
Underneath the remote trick is a genuinely ambitious piece of 1973 engineering. The QTA-790 is a 4-channel/stereo AM-FM receiver rated at 36 watts per channel into 8 ohm loads, and Audio (July 1973, p.42) measured it at an honest 35 watts per channel with all four channels driven simultaneously — close enough to the claim that the reviewer chalked the gap up to a meter needle's width. That's 140 clean watts total, not the "280 watts total ± 1 dB" figure Radio Shack's own literature floated. The magazine took the company to task for that bit of spec inflation while praising the receiver itself, a fair split: the hardware was good, the marketing was loose.
The tuner section is specified at 2.0 µV IHF sensitivity with a 60 dB signal-to-noise ratio and 0.3% THD in mono, capture ratio a tight 1.5 dB, selectivity 55 dB, image rejection 78 dB, and stereo FM separation 35 dB. In testing, separation at low and mid frequencies came in at 40 dB — better than claimed — tapering to about 25 dB at 10 kHz, and selectivity measured 58 dB, also a touch better than the spec sheet promised. Audio (July 1973, p.42) reported pulling in 54 signals on a stationary outdoor Yagi aimed at New York City from about 20 miles out, and found sensitivity excellent across the dial rather than just at mid-band. The AM side is more modest: 7 µV IHF sensitivity, 23 dB selectivity, 50 dB S/N, 45 dB image rejection.
The amplifier's power bandwidth is quoted at 18 Hz to 45,000 Hz, and the review confirmed it exactly as claimed. Frequency response runs 20 Hz to 30,000 Hz with no tolerance given. Below roughly 25 watts, THD hovered around a very low 0.1%; IM distortion sat near 0.2% below 20 watts and reached 1% at about 28 watts per channel. At half rated power, THD stayed under 0.5% across the entire audio band. Phono input impedance is 50 k ohms, with high sensitivity at 5.0 mV and low at 2.5 mV; aux is 200 mV, and tape input is adjustable from 0.2 to 2.0 volts — a thoughtful touch for matching the wildly different line levels of reel-to-reel, 8-track, and cassette decks of the day. Tone controls offer ±12 dB at 100 Hz for bass and ±12 dB at 10,000 Hz for treble, plus a mid-range control centered at about 1500 Hz. The reviewer found that midrange midpoint a bit high in frequency but effective in use and worth having — it behaves like a presence control.
Build quality is where this receiver surprises people who assume Radio Shack meant cheap. The front panel is a single solid casting with a blackout plastic insert up top, a brushed-gold aluminum panel below, and polished gold-colored framing around the perimeter. The blacked-out section holds the signal-strength meter, the AM/FM dial scale, a softly illuminated pointer, and five small vertically calibrated dials for station presets, with combination rotate/push buttons directly beneath them. Dual headphone jacks are provided for four-channel listening, and dual concentric clutch-type bass, treble, and mid-range controls keep the front panel from turning into a knob farm. A mode switch covers stereo front-only, SQ matrix, stereo-all (two-channel material fed to front and rear), and Aux 4 for discrete four-channel sources. Three slide controls handle balancing: horizontal sliders for left-right on front or rear, a vertical slider for front-to-rear level.
Inside, the chassis is neatly laid out across 12 separate modules. The Alps FM front-end is remarkably small because it contains no variable capacitor at all — tuning is done electronically by applying regulated DC voltages to varactor diodes. Each station preset is simply a multi-turn potentiometer picking off a set voltage; even the manual tuning knob is geared down to a single-turn pot that scans the voltages from 88 to 108 MHz, which is why there's no flywheel. The FM i.f. section is elaborate by the standards of the day: a permanently tuned ceramic filter, three interstage transformers, three transistors, an integrated circuit, and a conventional ratio detector. The SQ decoder board uses 15 transistors for the phase-shifting, summing, and decoding. Each of the two power output modules carries four 2SC1111 silicon output transistors in TO-3 housings on substantial heat sinks. The remote control receiver module accounts for 21 transistors, and the preset remote module adds ten more plus three ICs and five relay switches.
The back panel is practical in ways that reward long ownership. Speaker terminals for up to eight speakers — two full sets of quadraphonic systems — use "piano key" clamps that grip stripped wire ends and effectively prevent cable shorts. Four pin jacks paralleling the A speaker terminals accommodate speakers with pin-plug connectors. There are screw terminals for external AM antenna and 300-ohm or 75-ohm FM antennas, two unswitched convenience AC receptacles, and a holder for 3-ampere fuses. Tape facilities allow dubbing from any selected source to two recorders at once, and the tape playback jacks have their own input level control. The line cord even ships with a metal clamp that, connected to the FM antenna center terminal, turns the cord and house wiring into a makeshift antenna — the reviewer disconnected it and hooked up a real antenna before listening tests, which tells you what he thought of that idea.
Two honest caveats from the period testing. FM mono performance was without flaws, but the reviewer was slightly conscious of distortion on stereo FM stations, and frequency calibration on the test unit ran about 500 kHz off at the low end and 150 kHz at the high end — correctable with more careful alignment of the electronic voltage-tuning circuitry. The muting circuit also proved overeager in a few situations until the mute button was disabled. On the amplifier side, the 35 watts per channel drove low-efficiency air-suspension speakers to loud levels, but at genuinely ear-shattering volume, bass overload showed up on some rock passages. With four speakers and the stereo-all mode engaged, the receiver effectively adds 6 dB of sound pressure even from stereo sources, and 36 watts times four was judged more than enough for an average 14 × 19-foot living room.
At $598 including the wood cabinet and the separate remote control unit, the QTA-790 undercut much of the four-channel competition while offering most of what a budding quadraphonic enthusiast wanted. Audio (July 1973, p.42) closed its profile with exactly that verdict: the complexity possible in a four-channel receiver goes beyond what this Realistic offers, but so do some of the prices, and at $598 it delivered many of the goodies a buyer was likely to look for — and likely to be able to afford. The earlier Audio (January 1973, p.34) new-product notice counted no fewer than 103 transistors in the receiver plus two more in the remote, and rated it 4 x 36 watts continuous at 8 ohms.
For collectors, the QTA-790 sits in an interesting spot: a genuine varactor-tuned, remote-controlled quadraphonic receiver from the first wave of four-channel, sold through Radio Shack rather than a hi-fi salon, and built with a seriousness the brand didn't always get credit for. The motor-driven volume remote is the party piece and the most likely thing to need attention — a geared miniature motor and a 21-transistor receiver module are not trivial to service, and the five station presets depend on potentiometers that can drift. The electronic tuning means no dirty variable capacitor to clean, but it also means alignment matters, as the test unit's calibration error showed. Buyers should expect the usual quad-era realities: the SQ decoder is of its moment, and stereo use of a four-channel receiver ties up only two of the four amplifier channels unless the stereo-all mode is engaged. None of that diminishes what the QTA-790 is — a well-laid-out, generously equipped receiver that Radio Shack priced aggressively and, by the measure of the day's press, largely delivered on.
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.