Last I remember that logo was our mid-50s canister vacuum.
I can't definitively say when the 3-B became the standard. But we moved it to our new house in summer 1957. Fullsize, slantfront, chevron door.
Few differences from the late 40s before it. Suspension, identical. Solenoids, identical, though the spin solenoid performed a slightly different function in the transmissionless. Timer and cycles, identical. Pump coupling went from the older flatmetal spring to the newer coiled spring. New pump cover included hose nipple for diaphragm waterlevel sense. Previous waterlevel sense was a switch on the bottom suspension spring. Older, double door; newer, single door plus boot. Yes we had to have the boot replaced, the only repair I couldn't do. I was ~13yo and rebuilt the pump coupling and spin clutch. Pritdang good value for 50c/week allowance.