From the speaker date code and other clues, this is a mid 1957/mid 1958 Ampeg M-12 Mercury. Likely a product of Ampeg’s transitional period during their move to Woodside, NY. Definitely a special amp with lots of character. Groovy “Pollocked” grill cloth. Jensen Alnico 5 speaker. And no tolex here...
Found with components dating to no later than November 1960, it could be one of the earliest B-15N’s produced.
We’ve nicknamed it “Number 24” after the hand- numbered chassis.
As Ampeg began development of the B-15-N in the latter part of 1960, a few models were released lacking the more elaborate cosmetic elements typical of the B-15N...