He used those old Acoustics in the early days because they were about the only amps going that really projected your sound, they were about the only thing going for big and loud until SVT's came along and blew them off the face of the earth a year or two later. That being said they are cool amps but I only tried one once years ago and didn't really like it as they only sound good when you are way out in front of them, up close they have no balls at all, they project the sound out into the audience which is why they were good for big stages.
The Acoustic amps appeared as his backline some time in 1969 and were only replaced, I think, in about 1977 or so. Prior to that I assume he was using either the Rickenbacker Transonic amps the band had very early on, Arbiter Power 100s (as seen in the Danmarks radio footage, maybe?) or whatever was available on the gig. For example I presume he's using the WEM amps seen in the Supershow footage from 1969.
Having said that he could have used anything in the studio. I think he used a Fender amp on Heartbreaker, and there is certainly some dirt and a tremolo effect on the recording.
