The original MOSFET, a VP0106, is hard to obtain and not particularly
good.  We are presently using an MTP5P06V from Farnell, $3.14 each,
Farnell part 300-5689.


Was Motorola, now "ON Semiconductor", www.onsemi.com
  P-channel
  Vss=60V
  Rds=0.45ohm (much better than VP0106, which is more like 6 to 8 ohms)
  Id=5A
  Vgs=4V max


Pinout for TO-220 case is (looking at front, i.e. with metal tab to
rear, epoxy to front)

   _____
   |   |     1 = gate
   |   |     2 = drain
   -----     3 = source
   | | |
   | | |
   1 2 3