Heathkit
Heathkit sold electronics as kits for 45 years, and its two entries in the archive show both ends of its hi-fi range. The W4-AM is a 20-watt Williamson-type power amplifier with push-pull 5881 output tubes; the XO-1 is a tube electronic crossover for splitting the signal between bass and treble amplifiers, which the seller used with Altec and JBL speakers.
With any kit, the original builder matters as much as the design. Heath's manuals were famously clear, but solder joints, lead dress and substitutions vary from one example to the next. Look underneath before you buy.
The Heathkit maker page covers the company from its aircraft-kit origins to the end of kits in 1992, and the signal-path guide explains the Williamson design the W4-AM follows.
