Here are two methods. If you want an approximation, a maximum length feedback shift register sequence will work.
An electronic method is to reverse bias a BJT base emitter junction with a series resistor to limit the current once it breaks over (Zener action). Follow this with an amplifier to get the level to what you want.
If you want extremely wide band noise there are special tubes you can buy.
you can make one from a 5v or 6 v miniture light bulb
just blow the filliment with 12 v paint it with conductive paint paint in a small conductor
and use this too provide a field signal
any field signal is white noise connected too a bjt
some instuments use this approch
as above
but this isnt a special one but its a cheep one