Wow!!!
75 NiMH 2300mAh cells...It must cost a small fortune!
If you have not bought them yet I would suggest buying a 12V car battery and make two pulsed power supplies - one for 90V and one for 9V.Both simple and cheap.As well as much more reliable.
But since I think you already have these cells,I advise you to use a very simple circuit to charge all the 75 cells simultaneously.Imagine the following circuit: a capacitor,a resistor and a bridge rectifier.The battery pack is connected to the +/- outputs of the rectifier that is connected to AC mains through the current-limiting capacitor and the resistor whose function is to limit the initial charge current.Very simple and very dangerous,too,because the circuit is hot.But if You take some safety measures it will not be a problem.
And,of course,a timer to limit the charge to the necessary value.