About as pretty and pristine as the come: pictured and ID'd on page 46 of of Hans' book along the left side. Auction Link Here Gabby auction text but with few details.
The safe guess would be 10" but there's probably enough height/width for a 12". Public domain schematic indicates 2X6L6s running near 385 volts. Hard to believe anyone would go to that much trouble and put an 8" speaker in there. Hand-drawn schematic Apparently the seller's 'research' excluded actually looking at the amp; you know, stuff like measuring the speaker or looking at the tubes. :evil:
Masteramps of this period typically have a 12 inch speaker. Sometimes you'll find them with a 15 inch. There is even a hi fi model that came with a pair of tweeters!
Oops, Oh yeah I forgot. The seller e-mailed me and said that ebay cancelled his auction as there was something fishy with the last minute bidder that out bid me. I think he's going to re-list it.