I have this medical instrument that runs on 4 AA batteries which in turn powers a bulb. It also has a non-illuminated switch to turn it On/Off. Is it possible to have it run on an ac-dc power supply and convert its switch to an illuminated one?..
regarding the power supply,
if you want to maintain/regulate the output of this supply equal to 4 AA-batteries (which equivalent to 6 Volts),
the simpliest, i think, is to use a 7806 regulator IC