thanks to replies. According to the datasheet the VCC of of C is higher
than HC part. In the capacitance meter i am planning to make, its
supply voltage is 12 volts but 74hc14n VCC pin max is 6 volts only.
That might be the problem. With the transistor tester using also 74c14,
its supply voltage is 6 volts. In this case, the 74hc14n might be
suited as substitute but not in the capacitance meter with the supply
voltage of 12 volts. (Because 74c14 has a Vcc ranging from 3.5-15 v but
74hc14n only up to 6 volts). Am I right?

tnx again,

ian