hi All
Im experimenting with single transistor amplifier. I am using NTE 396 in the following circuit:
here are some notes on the circuit:
- The 10 ohm resistor on the far right represents what would be a speaker
- The transistor is NTE 396 which is a small power transistor
- The transformer primary resistance in pure DC is 26ohm
- Im feeding it 19Volts since i want high power output
- note that my base bias resistor is 590Ohm (not 550 as it says). so i calculate the current in pure DC to be (19-0.7)/590=31ma
- the DC voltage i measure is 4.75 volts on the primary of the transformer. so it works out to about 4.75/26=180ma current. This gives a beta of only 180/31=5
here are my questions:
-Why is the measured current (and voltage) on the primary of the transfomer, in pure DC, not much higher? how come the beta is only 5?
- Assuming the transistor has beta of at least 50 this works out to a max of 1.55Amps (with 31ma base current). With 19Volts, i would expect then expect around 18 volts dropping on the transformer and current to be like 18/26=0.7A. so why is it only 180ma?
- Also (i know its bad) the transistor has turned brown (it still works but has browned up). any ideas why? i would expect it to be able to handle 180ma wihtout browning
Thanks
Im experimenting with single transistor amplifier. I am using NTE 396 in the following circuit:
here are some notes on the circuit:
- The 10 ohm resistor on the far right represents what would be a speaker
- The transistor is NTE 396 which is a small power transistor
- The transformer primary resistance in pure DC is 26ohm
- Im feeding it 19Volts since i want high power output
- note that my base bias resistor is 590Ohm (not 550 as it says). so i calculate the current in pure DC to be (19-0.7)/590=31ma
- the DC voltage i measure is 4.75 volts on the primary of the transformer. so it works out to about 4.75/26=180ma current. This gives a beta of only 180/31=5
here are my questions:
-Why is the measured current (and voltage) on the primary of the transfomer, in pure DC, not much higher? how come the beta is only 5?
- Assuming the transistor has beta of at least 50 this works out to a max of 1.55Amps (with 31ma base current). With 19Volts, i would expect then expect around 18 volts dropping on the transformer and current to be like 18/26=0.7A. so why is it only 180ma?
- Also (i know its bad) the transistor has turned brown (it still works but has browned up). any ideas why? i would expect it to be able to handle 180ma wihtout browning
Thanks