Heathkit AA-21 (1960s)

The Heathkit AA-21 is a solid-state integrated stereo amplifier sold as a kit, introduced in 1969. It was a substantial unit — 70 watts RMS per channel into 8 ohms, weighing in at 30 lbs, with a frequency response of 10Hz–50kHz ±0.5dB. Total harmonic distortion was rated below 0.5% at full output across the 20Hz–20kHz band. It was a serious piece of iron for the home builder.

The design used transistor-based preamp and power amp stages, the latter with a complementary symmetry output. The regulated power supply had separate windings for the preamp and power amp sections. The phono stage offered RIAA equalization with 2.5mV sensitivity (65dB signal-to-noise). Line inputs needed 1.2V for rated output (75dB S/N). Inputs covered phono, tuner, aux, and tape, with a tape output and two pairs of speaker terminals. Controls included bass, treble, balance, input selector, and tape monitor, all on a brushed aluminum front panel. Dimensions were 17" × 5.5" × 13.5".

Heathkit's advertising of the era leaned hard on the economics of DIY. Audio (August 1964, p.73) ran a full-page ad comparing three paths to owning a transistor stereo amplifier: designing your own from parts (estimated at $170), buying one assembled (from $204.90 to $812.00), or building the Heathkit AA-21 at $139.95. The ad pitched building the kit as "the best way," and the same campaign appeared in High Fidelity through 1964.

There is a wrinkle in the dates. The fact sheet gives 1969 as the introduction year, yet the magazine ads above are from 1964. The record is thin, and the two dates can't be reconciled with confidence. The AA-21 was a well-specified, all-transistor integrated amp kit, positioned as a high-value build-it-yourself project.

Beyond the specs and the ad campaign, very little is documented. No owner reviews, no service notes, no collector pricing, and no end-of-production year have surfaced in the research. Anyone who owns one or has rebuilt one can send details to the archive.

Power: 70W RMS/ch into 8Ω
Frequency response: 10Hz–50kHz ±0.5dB
THD: below 0.5% at rated output, 20Hz–20kHz
Inputs: phono (2.5mV), tuner, aux, tape
Outputs: tape, two pairs of speakers
Weight: 30 lbs