Heathkit AJ-10 AM-FM Stereo Tuner
A tuner kit that turned nervous first-time builders into DX hunters - and made one magazine's test subject a believer.
Overview
The AJ-10 is a Heathkit AM-FM stereo tuner that arrived as a box of parts and a promise: follow the book, and a working tuner comes out the other end. Tape Recording (December 1960, p.26) tested that promise by handing a kit to a complete novice. By the magazine's own account, he knew nothing about the innards of a radio set. No help was given beyond the instruction to follow the directions to the letter. The magazine's stated reason was simple: kits save money, and tuners like this one can be put to work alongside a tape recorder, which was the readership's world.
The AJ-10 is not a simple kit. It carries both an AM section and an FM section sharing a common power supply, and Tape Recording called it "the kind of kit that makes a man of you all at once." The construction follows the classic Heathkit method: large pictorial diagrams show exactly where each part goes, and each step is written out in plain text. A resistor is named by value and color code, trimmed to a specified lead length, and connected between a numbered lug on one component and a specific point on a tube socket. Exploded views appear wherever the going gets complicated. The magazine said the point-to-point wiring "is not at all difficult," and compared bolting the sockets and condensers to the chassis to assembling an erector set.
The novice builder in the Tape Recording piece finished the tuner and came out on top. The magazine reported that he was soon talking about tackling an amplifier to go with it, and that his wife was pleased with the fine sound. The article also remarks that wives make excellent solderers and wirers, and that one is almost a necessity when stringing the dial cord. That says something about who built these things in 1960.
A note for anyone servicing one today: Heathkit issued a schematic correction for the AJ-10. The B+ supply for indicator tubes V11 and V12 comes from the +112vdc bus at the right end of R47, as shown in the assembly instructions on page 36, not from +140vdc at the left end of R46. If a unit was rebuilt from an uncorrected schematic, check that before chasing a fault in the indicator circuit.
The AJ-10 was succeeded by the AJ-11, which Heathkit advertised as the "successor to the popular AJ-10." The AJ-11 added flywheel tuning, two "magic-eye" tuning indicators, and adjustable FM automatic frequency control. HiFi-Stereo (May 1961, p.29) ran the announcement under the heading "Introducing a New Styling Concept in Two Popular Heathkit Stereo Units."
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