50W 2x12 from the space-age 143X series (1959-61).
Marks that can be entered for this maker: Transformer code, Chassis stamp.
Nothing predates 1959; components only push the date later.
Sold-price aggregates are not collected yet, so the archive gives no figure — condition, originality of the transformers and a documented recap move this model more than any list price.
Evidence: Blue Book of Guitar Values — silvertone · Silvertone World — model 1434