ok here we are even here in Canada some of these parts number are
not "on the shelf " thing
2n4124 can be replace with 2n3904
as for the 2 others this what the specs are "close enough"
if you go to a GOOD reseller finding a match should be a breeze
good luck
http://pdf1.alldatasheet.com/datasheet-pdf/view/183702/IRF/IRGB14C40LPBF.html
as for the hall sensor, pick a number that will suit your project application
and respect polarity and you'll get a spark:fan:
Be careful specifying the 2N3904 as a replacement for the 2N4124...
It'll likely work, but the circuit wasn't designed for that unit. The 2N4124 has much higher DC current gain (Hfe or Beta) than the 2N3904, especially operating at a switch. When a transistor is operated as a switch (i.e. in either saturation or cutoff), the DC current gain is dramatically reduced. You often have to dig in the datasheet for this information.
In any event, replacing it with the 3904 will cause more base current to be drawn from the input circuit and will change the duration of the "timeout" feature.
In fact when I was designing the circuit, I originally had the 2N3904 or 2N2222A in mind since they are so easy to get. But, to ensure things would work for others the way they did in my prototype, I rejected those. The DC current gain was marginal - right on the edge of being OK.
Just keep in mind that I designed the circuit around the 2N4124's characteristics. This holds true for the other parts as well. Switching to other parts is done at risk of things not working as expected. It's hard for others to support problems if things are changed that have no verification history.
All that said, many of the parts are not Radio Shack items. But, all are available from Digikey or Digikey Canada (digikey.ca). Apart from the transistors, the LED specified is also crucial. They do more than just light up as a timing indicator... They are also part of the timing.
To all, build the circuit using the parts list and schematics from Dave Sage and I and you'll run less risk of things not working.
This isn't meant as a dig at Luc. Sometimes my writing style can be abrasive without intending it... Luc has done excellent work supporting this circuit, especially since I haven't kept up with this thread as well as I should have.
John