I purchased this great amp used in 1989. The A 28745 serial # stamped on the chassis indicates a 1968 model. The amp was missing the tilt-back legs and the tolex on the bottom back panel. I used the amp a lot in the 90's and just a few times in the past couple decades. In 2008 I had Acusonic clean up, fix and update a few things. Please see the pic of the repair receipt. The amp has four CTS alnico speakers. One of originals was swapped out instead of getting reconed many years ago. It's a slightly newer CTS speaker w/date code 064121 indicating it's a 1974. The input and output transformer date codes (606-7-43), (606-7-40) both indicate manufacture in 1967 by Schumacher the 43rd and 40th week of 1967. The Reverb and tremolo work great. The amp is a classic with awesome warm tone and break up. I recently had a amp tech review the chassis pics and we confirmed the amp has the silverface AB568 circuit. However, since the 1968 model uses the same transformers as the earlier blackface models, I'm told it is a relatively simple process to revert the amp back to the blackface circuit.