Info on compatible joystick

Mine is a PC Joystick (15 pin connector). It's exactly the same markings, same buttons. Everything.

Yes there will be HUGE problems with the incorrect pots in there.

You can make adapters that'll allow you to use the incorrect pots, but it's a bit of work. I tend to refer people to Quinn (of BlondiHacks) as writing a good primer on it: http://quinndunki.com/blondihacks/?p=2225

Chesh.

The potentiometers are 1.4Mohm, while in the original Apple are 150Kohm; can there be problems ?

Quinn Dunki's article discusses how to compensate the computer's internal timing circuit by adding capacitance to the joystick's internal pots which in this case are too low of a resistance - 10K ohm in her case.  Bus tince we want to go the other way - lowering hte total resistance the computer sees...

You can add some compensating resistors to the pots.  Being 1.4 Meg ohm pots, adding 160 K ohm of resistance in parallel will get you 143.6 K ohm.

However, you may have to experiment - I've found that lowering the total resistance to say 110 - 120K works better for joystick linearity. 

There are many Apple II joysticks (like the very popular TG Products joysticks) that have high value pots with compensating resistors.  In the case of the TG, the effective equivalent resistance is just that - about 120K.

You can then use a graphically based diagnostics tool like the MECC Computer Inspector to see how well your joystick's linearity is visually on the screen.