What a very curious setting for this shot, with its nice parquet floor, panels of flock wallpaper, its ornamental column and posh chandelier (not in full swing but casting a Damoclean shadow over Mr Brooker) compromised by a heating-pipe and a little electric clock advertising Lowrey organs (as favoured by The Band at the time). It must have been lit with at least two lights, judging by the shadows; yet the fussy background suggests a lack of preparation or forethought.
It looks to me as though Gary is sitting at one of these Lowreys, especially as it seems so very similar to the one the other side of the picture. All the amps are Selmer's Truvoice Bassmaster 50 model, and all the gear still has price tags attached to the carrying handles.
Robin is plugged into the treble channel of his, and a pick-less Diz into the bass channel of his as would be expected: he also gets the double-sized speaker cabinet, presumably a 4 x 12. The guitars are the same Gibson semis that were played on the beach in an another shot: see also the band's promo photo.
It seems puzzling that two guitarists merit three heads and three cabs, until one realizes that the third setup is there solely to mask the absence of a drumkit, its lead artlessly vanishing into Barrie Wilson's lap, where it might more sensibly have gone towards a vocalist's microphone. (RC)
Frans Steensma adds:
This ad for Selmer also appeared in the insert of the Whiter Shades Of R&B album, but more interestingly: when Selmer used this photo in MM (21 November 1964) they simply cut off the other three and only used the far right part of the photo featuring handsome Diz (+ Selmer amplifier) ... wonder if the other three were very happy with that move? (more from Frans here)