Hi Andrew

Try using PNP transistors in the "top" legs of the H, and NPN in the "bottom" legs.

Also use biasing resistors to switch the transistors off (base to GND on the NPN

and base to + on the PNP)

You have to invert the drive signals (transistor 1 = PNP drive base low, and transistor 4

= NPN driven high)

Thats the way the bridge normatty operates :-)

I think your problem is that both transistors in a leg are being switched on together, thus

shorting the supply and cooking transistors.

Cheers

Mark