Introduced in 1973, the model 90 was a cost down exercise with a hint of practicality mixed in. Only a few year separated the 75 to 90 (13yrs) in comparison the the years that pasted betwixt the 1227 and 75. (22yrs). However the changes made between models were unsubstantial, with the change back to a single piece lamp shade being the most recognisable feature.
Regrettably this is the point where Anglepoise moved from reliable rocker switch, to the forever troublesome push button option. For those lucky enough to have used both 75 and 90 and made the mistake of grabbing the very hot shade ( courtesy of the incandescent bulb ) while trying to stop the lamp being pushed away rather than switched on will lament the rocker switch demise.
If you find yourself fondling a dusty box of Anglepoise parts and find a base plate and fork of unknown variety, the 90 forks were shorter than the 75.
Most regrettable to me was the design and I expect value engineering lead decision to remove adjustable springs. I can appreciate the reasoning and the cost saving having made a few sets myself, I understand the time and effort involved. However I value the joy and personal experience of fettling a saggy lap into fine equipoise, now a experience deprived from the masses.