Hewlett-Packard’s first product in 1939 was an audio oscillator (sinusoidal signal generator) which became famous in the industry when a Disney sound engineer used eight of them to create audio effects for the animated film Fantasia. That model, and direct descendants, remained on the market until 1972. But, times change, and by the 1960s H-P had extended their offerings to include function generators able to output sine, triangle, or square waves over a wide range of frequencies into the megahertz range, built with transistor technology. The Model 3300A was a flagship of this era, with a temperature-stabilised master oscillator and an extremely clever way of generating a precise and stable triangle wave and then synthesising the other waveforms from it.
In this video, a vintage 3300A is debugged, repaired, and calibrated to restore it to as-new performance, while digging into the circuitry that does the job.