The 100W 4 x 6550 Model T — the amp that became the doom/stoner-metal icon.
Marks that can be entered for this maker: Transformer code.
Nothing predates 1960; 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 — sunn