Heathkit W4-AM
Twenty watts of Williamson circuit for under forty dollars, if you were willing to hold the soldering iron yourself.
Overview
The W4-AM was Heathkit's single-chassis take on the Williamson amplifier — the classic circuit that, as Heath's own catalog copy put it, still accounted for the largest share of power amplifiers in use years after its introduction. The pitch was straightforward: a 20-watt amplifier carrying "all of the advantages of Williamson circuit simplicity with a quality of performance considered by many to surpass the original Williamson." That last claim is marketing, not measurement, but it tells you exactly where Heath positioned the kit — as a faithful, affordable route into a circuit that had already earned a following.
The number that mattered most to a 1950s builder was the price. Heathkit listed the W4-AM at $39.75 in its 1958 catalog pages, which put a genuine Williamson-type amplifier within reach of someone who couldn't swing the bigger iron in the lineup; the same Audiocraft (February 1958, p.12) advertising spread carried the 25-watt W-5M at $59.75 and the 70-watt W-6M at $109.95. For context, the same catalog spread carried the dual-chassis W3-AM at $49.75, the 25-watt W-5M at $59.75, and the 70-watt W-6M at $109.95. The W4-AM sat at the bottom of that ladder — the entry point, not the flagship.
What you gave up for the price was a separate power supply. The W3-AM split its power supply and amplifier stages across two chassis so they could be stacked or set side by side; the W4-AM crammed everything onto one. For most home builders that was a feature, not a compromise — fewer chassis to drill, fewer interconnects, a tidier shelf. The shipping weight ran 28 pounds, which is a fair chunk of transformer and iron for a 20-watt amp.
The circuit itself is the reason these still circulate. The Williamson topology was prized for simplicity, and Heath leaned hard on that heritage in its copy, promising "many pleasure-filled hours of listening enjoyment." Twenty watts is twenty watts — but twenty watts of a clean, simple, well-understood circuit with service documentation still floating around is a different proposition from twenty watts of something obscure.
Heathkit's own advertising is the main period source that survives in usable form here, and it's worth reading it as advertising. The claim that the W4-AM's performance "surpasses the original Williamson" is Heath selling its own kit, not an independent lab verdict. What the catalog does establish reliably is the price, the 20-watt rating, the single-chassis layout, the Williamson lineage, and the shipping weight — the bones of the thing. Owners who build or restore one today are working from the same manual pages that were packed in the box, which is the quiet advantage of a kit that sold in these numbers.
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