The differences between pre and post CBS did not occur overnight. They didn’t immediately end manufacturing and switch sources or make dramatic circuit changes for no reason. Most late blackface used the same components as silver face and silver face used mostly the same blackface parts. Circuit changes were mostly done to accommodate newer part specs or to save money in production. Having been a truck for 50 years it’s typically the engineer at the time initiating improvements based on amp failures seen coming in for repairs. Eventually cheaper parts and lower cost employees building gear invites mistakes and damages sales due to gear performance or failure. Fenders are simple and cheap to upgrade so any that have the basics like pots and transformers in good shape can be refurbished to run like new is you lay the hocus pocus to rest and focus on the basics.

The guy with the “1966” Bassman with the AA864 probably has a 1964 and does not know it. He thinks its a 66 due to the “Patented 66” on the front panel. Its a common mistake. He should verify the chassis serial number, and internal stamp along with the pots and serial numbers on the transformers.

Ah, the fuzzy gray years between sale and handover. Or if your really that keen you need to date your amp to DD/MM/YYYY, the ‘What’s on the shelf’ period. Leo, bless him, was a practical man. He designed the best amps in the world for as cheap as he could. There has been lots written about what was going on at this stage at Fender, but basically be happy you have a Blackface. Trying to date them is a joke. And the secret is not in the board, it’s in the circuit.
Happy owner of a nominally ’66 Bassman.
Cheers, John.
PS My sticker says AB 165. It’s not, it’s a AA 165. Just using up those AB stickers before the sale instead of ordering new ones for AA 165. Either that or they ran out of AB 165 boards and had plenty of AA’s left.

I have 2 Bassmans. They never put a crossover in them. I can’t imagine why anyone would. You want a full range speaker cabinet. Check the ohms of the speakers. If they’re 8 ohms just wire them in parallel and get rid of the crossover. If they’re 4 ohms somebody might have put it in there if the crossover made the ohms load in the 4 ohm range. Don’t ever run the amp with less than a 4 ohm load. It’ll cook. 8 ohms is fine. If the speakers are 4 ohms wire them in series. You lose a touch of volume but not enough to matter. The amp will actually sound a touch tighter with 8 ohms. Tubes will last longer and it will run cooler. If you’re using it for guitar it’ll be plenty loud with the best sound you’ll ever hear. I put 4 10’s in one of my cabinets and it kills, even with a bass. One has the original Altec 15. It’s a bit muddy. But using them together gives me enough power to keep up with the band on bass. Looks cool, but it’s a workout hauling all of it around. Thats why the wheel and handcarts were invented.

Back in 1970 I bought a 66? blackface Vibrolux that came with (I thought) a Bassman speaker cabinet.
I have tuned up the amp a couple of times, but the Bassman cabinet just recently stopped working. When I opened it up, I found a crossover on the center cross bar. the speakers were both blue wire on the common to the red dot, and the yellow was hooked to the 2.5K Woofer connection. The 12″ Fender speakers had a part number of 023044. Did someone hack this 50 years ago? Did Bassman speaker cabinets ever have crossovers?