Questions about usage of the Bolt H Bridge

I built up the circuit at http://www.solarbotics.net/library/circuits/driver_4varHbridge.html on breadboard. Running it at 5vdc I hooked up a motor I had laying around
which I had pulled out of a 6V RC car (drive motor).
As I didn't have any 74HC14 parts on hand I used a 74LS14 to see if I could get the circuit up and see how things worked.
I also used 220ohm pull-up resistors for the A & B signals (and tied all other inputs to +5vdc).
Checking voltages at various points to see if the circuit was good I found +5vcd at both motor poles.
When I grounded B to start the motor it turned slightly and stopped, though if I gave it a hand start it would keep running.. I then noticed that Q2 was getting hot in a hurry.
I metered across the motor. Only getting about .5v. This is not what I expected.
I tried using the steering motor out of the same RC car. A much smaller motor.
Now when I ground A or B it runs the motor (reversing direction as expected) and I measure around 4v across the motor.
Both motors are causing my bench supply to jump from trivial amperage to around .3a when I make a connection.
Also when I hooked A & B both to Gnd with the intention of causing the motor poles to be low in the "off" state Q1 got hot in a big way very quickly.
I have a feeling this has to do with the motors "effective resistance". Unfortunately I really don't know how to figure this out for sure nor how to deal with it.
Looking for suggestions on what I am doing wrong and how I can fix it.
I have plenty of digital experience but anything analog always gets me.
Thanks, David
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Aaargh ! Ministry of crap design. Turn it off quick.
If you don't drive that line 100% then you will fail the smoke test.
Power could flow out from the base of Q1, down through the 2 resistors to the base of Q4 and short the whole thing out.
Suggest you redesign it. How about a small NPN taking power through a resistor on the base of Q1 to the base on Q3 (sort of diagonal) and the same for the other pair. That would give you forwards and reverse but don't turn both on at the same time.
best regards
Robin G Hewitt
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