Hello Everyone,
Not long ago I brought up the idea about using many small signal transistor in parallel for the output stage of a amplifier.
Someone said to try 1 amp small power transistors like the BD139.
I built up a test circuit with 6 BD139's paralleled in place of each power transistor that I am using.
As you normally use wire wound 5watt resistors on the emitter of each paralleled transistor to promote current sharing, this would mean that I would need 12 resistors to do the job.
As I didn't have them on hand or want to buy them just for this test, I decided to measure 12 lengths of cooper wire until I had 0.4 ohms for each length of wire. This would take the place of the resistors. By the Pic Attached you will see that I have wound all 12 lengths of wire on to one former in the middle of the test board.
I know that the heat sinks are too small, but I will be running each test for seconds not minutes, just to hear the effect.
So before I wire the board up, I decided to put a pic on the forum just in case it all goes up in smoke.
Not long ago I brought up the idea about using many small signal transistor in parallel for the output stage of a amplifier.
Someone said to try 1 amp small power transistors like the BD139.
I built up a test circuit with 6 BD139's paralleled in place of each power transistor that I am using.
As you normally use wire wound 5watt resistors on the emitter of each paralleled transistor to promote current sharing, this would mean that I would need 12 resistors to do the job.
As I didn't have them on hand or want to buy them just for this test, I decided to measure 12 lengths of cooper wire until I had 0.4 ohms for each length of wire. This would take the place of the resistors. By the Pic Attached you will see that I have wound all 12 lengths of wire on to one former in the middle of the test board.
I know that the heat sinks are too small, but I will be running each test for seconds not minutes, just to hear the effect.
So before I wire the board up, I decided to put a pic on the forum just in case it all goes up in smoke.