Sounds Incorporated, 1964-1966
Below, the well-known picture of Mary Wells with Sounds Incorporated, last third of 1964, from Getty Images. The amp caught at right is a thin-edged AC80/100 - its grille cloth 3 diamonds tall. The grilles of thin-edged AC50s are 2 2/3 diamonds tall.
The amp is seen on stage accompanied by two Foundation Bass cabs during the Arthur Howes/Epstein package tour of Great Britain, 9th October - 10th November, 1964, Mary Wells, Sounds Incorporated, The Remo Four, et al. supporting The Beatles.
Belfast, King's Hall, 2nd November, 1964. The amp and one of the Foundation Bass cabs (the other is behind the curtain) can be seen at right of stage.
Below, a further shot of an early AC80/100 belonging to the band - very probably the one above, caught in a photo from c. 1966 (venue at present unknown). At least one of the AC50s pictured has a three-line serial number plate and red warning plaque.
Salient features of the rear of the amp: twin Cannon XLR sockets; the rounded off corners to the white warning plaque (also on serial number 173); the metal Arrow ball-end mains switch; and the absence of screws on the top edge of the backboard.
Thanks to Ruth for the image.
A backup on hand for the concert at Shea, 1965
The film documentary on the The Beatles' concert at Shea (15th August, 1965) contains, around 10 1/2 minutes in, a brief glimpse of some of the equipment assembled for the show.
From background to middle-ground: the brown-fronted amp is probably one of the early AC50s (there as a backup); to its right, a thick-edged AC100. In the middle-ground, two amps placed front to front. Nothing much can be seen of the furthest one, but it may be another AC50 (given its apparent smaller size). The amp with its rear panel showing is an early thin-edged AC80/100. To its right a thick-edged AC100.
The amp with its back to the camera is not seen on stage at any point during the proceedings, so may have been a backup either for The Beatles or Sounds Incorporated. The arrangement of elements on its panel shows that it was not the early AC80/100 that Sounds Incorporated regularly used, however. See the picture from 1966, above. Note the positions of the mains socket and outermost speaker socket in relation to the screws on the lower edge of the back board.