The 1433 was the top of the single speaker line for this last phase of a discernible Silvertone 'line.' After the 143X series, Silvertone amps were less unified in look, and less similar from grouping to grouping. The innards also became more diversified, with some sonic changes coming as well.

Introduced:
Fall/Winter 1959 at $99.95
as the 57FO1433L

Through its career, it was :
57K1433L
57H1433L

Retired:
Spring/Summer 1961 at  $99.95
as the 57A1433L