He’s using an armature growler (YouTube link) to test the armature from a generator. Armature growlers (or just growlers for short) were commonplace years ago. Back when cars had generators ...

Barnes The Armature Works Heights Public Market ... The 1910 building was formerly the storage and maintenance facility for Tampa Electric's streetcars, contributing to the urban feel it ...

Skilled technicians then wind fresh, precisely measured coils onto the core, ensuring optimal electrical flow and efficiency. By restoring the armature to peak condition, the starter motor can ...