Heathkit UA-1 (1958–1962)
The Heathkit UA-1 was a small mono tube amplifier sold in kit form from roughly 1958 to 1962. At $29.95, it was one of the least expensive amplifiers Heathkit offered. It was mono, so you bought two for stereo, and the valve museum that documents it describes exactly that use: a pair run as a stereo setup. It was the entry point of the UA series, sitting below the more powerful UA-2, which shared the chassis and output transformer but offered more output.
The circuit is straightforward push-pull. A 12AX7 dual triode drives a pair of 6BQ5 (EL-84) output tubes, and a 6CA4 (EZ81) does the rectifying. Rated output is 12 watts RMS, with frequency response spec'd at 20 Hz-20 kHz ±1 dB. One source gives 12 watts at 5% distortion. Another claims under 0.5% THD at 9 watts. Different conditions, same general ballpark. The output transformer is 3,440 ohms center-tapped with 4, 8, and 16 ohm secondaries. The chassis is an unfinished, single-piece inverted U-shaped pan with all components mounted above. It's not a thing of beauty, as one reviewer put it, but it is a simple circuit. The front panel carries a volume control, and there are screwdriver-adjustable AC and DC balance pots accessible from top and bottom.
Hi-Fi Music at Home (May 1959, p.47) ran Heathkit's own advertising for the chairside enclosure kit in the same era, which gives a sense of the period context — Heathkit was pushing complete, furniture-style systems alongside bare-bones amps like this one. Owner reception is genuinely mixed: some call the UA-1 sweet and open with the right speakers, others find it lean on the bottom end or harsh at high volume. Common restoration notes: the original electrolytic capacitors dry out and need replacement, the selenium rectifier should be swapped for silicon plus a resistor, and the bias pots are prone to drift. The tubes themselves are all still plentiful on the used market.
A pair in good original condition has sold on eBay for over $300 (the quote is undated), while single units can still turn up at hamfests for under $100. Kit-built examples vary in build quality depending on who did the soldering. Check the joints and caps before trusting one with your speakers.
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