Eico Model 3150 "Cortina" (1968)
A 100-watt integrated amp with two complete amplifiers inside a three-and-an-eighth-inch chassis. It measured louder than its own spec sheet promised.
Overview
Eico's own advertising billed the Model 3150 "Cortina" as a 150-watt stereo integrated amplifier when the New York Hi-Fi Show rolled around in the fall of 1968. HiFi/Stereo Review (December 1968, p.80) reported that figure alongside the kit price of $149.95, or $225 fully assembled. The box that actually shipped carried a more modest claim: 100 watts total IHF music power into 8 ohms, with 40 watts per channel continuous. That number was conservative too. When Audio (June 1969, p.44) put a factory-wired unit on the bench, both channels delivered 42 watts apiece before distortion reached 0.15%. The reviewers kept pushing to 55 watts per channel with THD still at 0.3%. Objectionable distortion didn't show up until roughly 60 watts.
Eico packaged the 3150 in an unusual way. Instead of a shared circuit with a common output stage, the design uses separate printed-circuit boards for each channel - magnetic preamp, voltage amplifier, and driver sections. One channel's three boards are mounted above the chassis and the other channel's three are mounted below. It's a true dual-mono layout in a package just 3⅛ inches tall, and that's how the amplifier stays this compact while delivering this much power. The two halves share only the power supply, and that supply is dominated by a power transformer that takes up roughly a third of the amplifier's entire internal volume. Twenty-six silicon transistors, six silicon rectifiers, and twelve biasing and protective-circuit diodes fill out the count.
The front panel is a gold-finished heavy extrusion. Six rotary knobs run across the top: a three-position source selector (phono, tuner, aux), volume, balance, bass, treble, and a speaker selector covering main, remote, both, and phones. Six rocker switches below handle tape monitor, loudness contour, mono/stereo, low- and high-frequency filters, and power. A headphone jack and on/off indicator sit at the far right. Around back there's a line fuse, switched and unswitched AC convenience outlets, main and remote speaker terminals, a ground post, the three input pairs, and tape-in/tape-out jacks. One quirk: the main selector has no dedicated tape position, so tape playback and three-head monitoring both depend on flipping the tape monitor rocker rather than turning the source knob. It catches out first-time owners.
The published frequency response runs 10 Hz to 30 kHz ±1.5 dB, with power bandwidth from 10 Hz to 20 kHz at 0.5% THD, hum and noise 80 dB below rated output, and a damping factor of 35 or greater into an 8-ohm load. Intermodulation distortion is specified under 1% at rated output. Audio (June 1969, p.44) measured the 1% IM point arriving only at 56 watts per channel, with total IM at rated output a mere 0.5%. Tone controls offer ±15 dB at 50 Hz and ±15 dB at 10 kHz. The high- and low-frequency filters meet spec, but the reviewers flagged them as only 6 dB/octave. That's gentle enough that they're of limited use as scratch or rumble filters. If you need aggressive subsonic filtering, this isn't the amp for it.
Transient response is where the 3150 does best. Eico published a 3.5-microsecond rise time. Audio (June 1969, p.44) didn't measure it directly, but the square-wave photos showed it: the 10-kHz square wave was described as about the best the reviewers had seen in an integrated amplifier, or even a basic amplifier. In listening tests with a Cambridge recording of Bartók's Sonata for Two Pianos and Percussion, the amp cleanly separated the woody tone of the xylophone from same-pitched piano notes, a distinction muddier amplifiers smear together.
Thermal behavior is another point in its favor. In extended full-power testing on both channels, the rear heat-sink area ran warm to the touch but never hot — and normal musical listening at any reasonable level wouldn't generate even that. The electrolytics and other supply components are conservatively rated for cool operation and long life. Kit builders had it easy by integrated-amp standards, and the wired unit's dimensions — 14⅜ inches wide, 3⅛ tall, 8¾ deep — make it an easy fit on a shelf. The original pricing put the kit at $149.95 and the factory-wired version at $225.00, which in 1969 dollars bought a lot of measured performance.
For anyone hunting one today, the practical notes matter more than the history. These are kit-era amplifiers, so build quality varies unit to unit depending on who soldered it — a clean factory-wired example is worth the premium. The non-barrier speaker terminals offer less protection against shorted leads than modern binding posts, so inspect them. And the tape-monitor-dependent tape loop is a genuine usability quirk, not a fault. What you're getting is a compact, genuinely dual-mono integrated amplifier that outperformed its own specifications by a wide margin, with transient response that period reviewers ranked at the top of its class. That combination is why the 3150 has stayed on collectors' short lists while plenty of louder-looking contemporaries have faded.
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