ASTRA were one of the few companies producing quality gramophone accessories in the early 1920's.Their soundboxes, the Astra 1 & 2 are missing here.
The Astra 3 & 4 soundboxes, were based on the PIANINA/Seymour Superphone soundboxes. The quality of Astra soundboxes was superior to most.
The Astra 5 & 6 were some of the best soundboxes of the era and are directly related to the Expert and EMG soundboxes. The Astra 5 soundbox was advertised in November 1930. The Astra 6 with the Meltrope ring, in December 1932.