Testing a Harmony H303 Guitar Amplifier  🎵
Channel: 1 Minute Electronics
Date: 2022-11-16

A somewhat famous mini amp using 1950s technology but sold in the 1960s. The speakers were quite good for their size and weight. This particular unit has remarkably little hum for an amp with line voltage tube heaters.
As with any old vacuum tube device, even UL listed, there can be an electric shock risk. Some of these units did not have a fuse and most did not have a grounded chassis, though some had an isolation transformer.
The vacuum tubes are 35Z5, 50L6, and 12SQ7, so the 117 volt AC line needed only a modest resistance to provide 97 volts for the 3 tube filaments in series.
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