Assuming a JBT transitor is connected in such a way that 1k resistor is connected to the source of 12 volt and connected to the collector, and the emiter is ground, with that set up, the voltage across the 1k resistor should be zero since the base of the transistor is open so the transistor should be off. But i found that isn't the case when i use BC549 transistor. from 1-7v, that is correct, but after that, i start reading voltage across the resistor.

 

At a high enough collector voltage with the base left open, the transistor becomes unstable and "stray" currents will get into the base and try to make the transistor conduct. Set that circuit up on a prototype board, connect a voltmeter accrross the resistor and then connect a wire lead to the base of the transistor. Pinch the wire with your fingers and watch the voltmeter go crazy!

I cant recall what the BETA is for a BC459 but with a high BETA value that effect is more prominent.

Not to beet a dead horse but its like when you touch the inpit lead of an audio amplifier, your finger does'nt provide any audio to the circuit (unless of course your musically inclined! :lol: ) but the stray/static voltage on your body causes a huge "BUZZ" at the output.