1.JPG [1.50MB]
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Electronics and Circuits
Transistor connection. AM 1970 radio, generic.
4
hace 6 años
hace 6 años
Hello everyone. I need your help since I am repairing an AM radio device (recently it worked correctly) and when checking the transistors I find that on the board I have two of them of type NPN in which in one of them only the base is connected and emitter and on the other is connected base and the emitter and coloector are together. I cannot say what type of transistor it is because it does not put it in either of the two unlike the rest that it does. There are 2 questions:
-On the one hand, what is the reason for making connections like this?
-And on the other, are these transistors of any specific type for this type of connections?
I enclose an image if it helps.
Thank you very much in advance. 1.JPG [1.50MB]
1.JPG [1.50MB]
1.400
hace 6 años
Hello, to be sure you would have to take one to measure the terminals because they can be double signal diodes of the old or simple transistors used as diodes.
4
hace 6 años
Hello, They do not have numbering, that is what seems strange to me, the other transistors of the device do (they are Sc109, SF115, etc.), but these that are connected in this way, has nothing. When taking them out I see that they are NPN type, with values of 786 in collector and 787 in emitter, come on, a normal transient working correctly, but I do not understand why, what is the function and if it is correct.
1.400
hace 6 años
From what I said above, they can be double diodes. You would have to follow the clues and see where they lead to draw some logical conclusion.
4
hace 6 años
Hi Carlos, from what I could see, they are connected to 2 ends of the winding of the transistor ferrite antenna. Said winding is composed of 2 windings, one with 80 and the other with 8 turns. one end of each of the windings goes together towards one of these transistors, another end goes to another transistor and the remaining end is connected to the variable condensation. However I find no conclusion when using transistors instead of another component. Regards.
4
hace 6 años
Just, the others mounted on the board are SC109 and SF115, all of these are different types of encapsulates for transistors. As a logical explanation I will think that it was cheaper to mount transistors instead of a capacitor or even a diode. Thanks for the help, it has served as a light. Regards.
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