Transistor Tester Light Alarm Blinker Ticking Bomb Signal Injector

Transistors 2

Transistors 3

Here are 5 novel circuits you can build with any small-signal silicon transistors. You may use any odd transistors you have in the junk-box or take advantage of the special offer of 20 transistors for $2.40. Any transistors salvaged from Computer boards or having an odd type number can identified as either PNP or NPN by testing it with the SIMPLE TRANSISTOR TESTER described in this article. It does not give any other characteristics however, as these circuits are so simple that you can use any of them as a tester in themselves. The TICKING BOMB, for instance, is ideal as it uses both an NPN and a PNP transistor so that either one can be substituted with an unknown type. as precaution against reverse voltage you should include a 1k resistor in series with one end of the battery. This will limit the reverse current to 10ma while the electrolytic reduces the impedance of the supply to enable the circuit to operate.

The transistor offer contains 20 NEW and fully guaranteed transistors. They are not rejects or seconds. This offer has been made available by this Talking Electronics at almost cost-price to encourage new experimenters into the field of MAKING rather than looking and thinking. Some (Australian) electronics shop's are also participating in this offer so ask the manager of your local shop first, before sending for the offer.

the whole 5 circuits can be constructed on one piece of veroboard strip, 81 holes long by 15 holes wide. The cost of this is less than $2. The board can be cut into lengths for each project to make a neat and thoroughly presentable finish. The 81 copper strips run across the board and have been cut in the middle by the manufacturer, making over 160 useful contact pads.


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Do you have a number of transistors that have their numbers rubbed off or odd transistors of an unidentified type?

This circuit will test them and find out if they are PNP or NPN. It is short-circuit proof so putting a transistor round the wrong way will not damage it. The diagram is set fov NPN types.

Simple Transistor Testor

The terminals marked C. B and E can be alligator clips on short lengths of hook-up wire. The transformer T1 is a speaker transformer salvaged from a transistor radio. It can have any impedance such as 400:8 ohm and must be inserted so that the primary winding gives a feed-back to the secondary winding. When this occurs, you will hear a whistle in the speaker. Now you are ready to try all your odd types. Those that do not oscillate should be put aside and re-tested when the battery with its current limiter, is reversed at terminals A and B.

Transistor Tester

Light Alarm


Ticking Bomb

Signal Injector

Transistors 2

Transistors 3

This article was taken from Talking Electronics

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