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Simple homemade transistor testers. Radio circuits - low-power transistor tester

In this short review, we will consider the possibility of independently manufacturing such an interesting and useful household device as a simple tester. Such a simple device is very useful for quickly checking the functionality of radio components and for use in everyday life.

Despite the fact that you can buy a tester in stores at a fairly low price, self-assembly of such a small device will be excellent practice for any novice radio enthusiast.

The assembled device is very convenient and can be used even by masters of their craft. You can see a photo of the homemade tester in the review below.


Schematic diagram of a simple tester

Such a device includes a minimum number of elements for assembly, which are in use in almost any home or, if necessary, can easily be purchased at any radio parts store or even at a hardware store.

At its core, this is the only multivibrator that is assembled on a transistor basis. With its help, rectangular pulses are generated.


The current control circuit is connected to the multivibrator elements on a back-to-back and parallel basis using two color LEDs.

As a result, the circuit that is to be tested using the device is tested with an alternating current, which ensures high accuracy of testing.

Operating principles of the tester

An alternating current is removed from the main working component, which is a multivibrator, which in amplitude is approximately equal to that supplied by the power source. Any one above 3.7 V, for example 16 or 25 V, is suitable as a condensing element.


Naturally, with an open circuit, the LEDs do not light up. When the circuit is closed and current flows through the circuit, the LEDs light up. It's simple.

With such a device you can very quickly and efficiently check any element for operability or a circuit for a break in it. Very convenient for use at home, especially by a less well-prepared person. Do-it-yourself transistor tester - what could be simpler?


Such a device is assembled either using a simple printed circuit board or using a surface-mounted method. The scope of application also includes the ability to determine “plus” and “minus” when you do not know where they are in the element being studied. For battery use, you can use 2-3 AAA batteries to minimize the size of the device.

The second method of making a compact tester for use in a car. Such a device will literally have 2 main operating functions - the ability to display voltage “at ground” and the presence of 12 V in the circuit. Moreover, all this will be available literally by connecting one wiring to the machine’s network.


What you will need to create such a functional device:

  • regular medical syringe 5 cm3;
  • LR-44 batteries in the amount of 4 pieces;
  • two small LED elements with a resistor component;
  • a small piece of steel wire;
  • wiring with a clamp at its end.

Schemes of homemade automotive testers

  • Using a counter method, we solder both used LEDs in parallel;
  • Through the resistor used, one of the ends must be soldered tightly to the steel wire;
  • Install the batteries one after the other directly inside the syringe body. These were chosen because they fit perfectly into a five-cc syringe;
  • The probe is isolated from the syringe with a plastic tube, you can check the functionality directly in the machine in practice;
  • We check whether the LEDs on the 12V element light up.

So, the use of a tester you made yourself is more than necessary in everyday life. Believe me, such a small device will definitely come in handy, if not in everyday life, then in those moments when you need to check something in the electrical network at home or in a car.

Making a tester with your own hands can seriously raise the self-esteem of any person who does not believe that he can do anything with his own hands - all that matters is desire.

Photos of do-it-yourself testers

When assembling or repairing sound amplifiers, it is often necessary to select pairs that are identical in parameters bipolar transistors. Chinese digital testers can measure the base current transfer coefficient (popularly known as the gain) of a low-power bipolar transistor. Suitable for differential or push-pull input stages. What about a powerful weekend?

For these purposes, the measuring laboratory of a radio amateur engaged in the design or repair of amplifiers must have. It must measure the gain at high currents close to operating currents.

For reference: the transistor gain “scientifically” is called the base current transfer coefficient into the emitter circuit, denoted h21e. Previously called "beta" and designated as β, so sometimes old school radio amateurs transistor tester called "betnik".

You can find a huge number of options on the Internet and amateur radio literature. device circuits for testing transistors. Both quite simple and complex, designed for different modes or automation of the measurement process.

For self-assembly, it was decided to choose a simpler circuit so that our readers could easily make DIY transistor tester. Let us note right away that we somehow more often have to deal with amplifiers based on bipolar transistors, therefore the resulting device is intended to measure parameters only bipolar transistors.

For reference: previously, the editor-in-chief of RadioGazeta carried out measurements in the old-fashioned way: two multimeters (in the base circuit and the emitter circuit) and a “multi-turn” to set the current. Long, but informative - you can not only select transistors, but also remove the dependence of h21e on the collector current. Quite quickly, the realization of the futility of this activity came: for our transistors, removing such a dependence is one frustration (they are so crooked), for imported ones it is a waste of time (all graphs are in the datasheets).

Turning on the soldering iron, the editor-in-chief began to assemble a device for testing transistors with his own hands.

If your feet smell bad, remember where they come from.

After some googling, I found circuit diagram of a device for testing transistors, which is replicated on a fairly decent number of sites. Simple, portable... but no one except the author himself praises it. This should have been confusing right away, but alas.

So, the original circuit (with slightly simplified indication and switching):

Click to enlarge

According to the author's idea, here the operational amplifier together with the transistor under test forms a source of stable current. The emitter current in this circuit is constant and is determined by the value of the emitter resistor. Knowing this current, all we have to do is measure the base current, and then by dividing one by the other, obtain the value h21e. (in the author’s version, the scale of the measuring head was immediately calibrated in h21e values).

Two bipolar transistors at the op-amp output serve to increase the load capacity of the microcircuit when measuring high currents. The diode bridge is included in order to eliminate the need to re-switch the ammeter when switching from “p-n-p” to “n-p-n” transistors. To increase the accuracy of selecting complementary pairs of bipolar transistors, it is necessary to select zener diodes (setting the reference voltage) with the stabilization voltages as close as possible.

I was immediately confused by the “not entirely correct” switching on of the operational amplifier with a single-supply supply. But the breadboard will endure everything, so the circuit was assembled and tested.

Shortcomings immediately emerged. The current through the transistor strongly depended on the supply voltage, which never reminds stable current generator. What the author of the circuit managed to select, while powering the device from a battery, remains a big mystery. As the battery discharges, the “exemplary” current will flow away and quite noticeably. Then I had to tinker with the “amplifier” at the op-amp output, otherwise the circuit would work unstably when measuring transistors of different powers. It was necessary to select the value of the resistor, and then I switched to a more “classical” version of the amplifier. And the bipolar (correct) power supply of the op-amp solved the problem with the floating current.

As a result, the diagram took the form:

Click to enlarge

But here another drawback has emerged - if you confuse the conductivity of the bipolar transistor (turn on “p-n-p” on the device, and connect the “n-p-n” transistor), and when selecting from a large number of transistors, you will definitely forget to switch the device sooner or later, then one will fail from the transistors of the “amplifier” and you will have to repair the device. And why do we need difficulties with bipolar power supply, opamp, amplifier, etc.?

Everything ingenious is simple!

I set out to make something simpler and more reliable. I liked the idea with a current source; by carrying out measurements on a fixed (previously known) emitter current, we can reduce the required number of measuring instruments (ammeters).
Then I remembered my favorite microcircuit TL431. The current generator on it is built from only 4 parts: Considering the not very large load capacity of this microcircuit (and it is extremely inconvenient to mount it on a radiator), to test powerful transistors at high currents we will use the idea of ​​Mr. Darlington:

Now there’s a catch - not a single reference book contains a diagram of a current source based on TL431 and a transistor "p-n-p" structures. The idea of ​​no less respected gentleman helped me solve this problem Siklai:

Yes, an inquisitive eye will notice that the currents of both transistors flow through the current-setting resistor here, which introduces some error in the measurements. But, firstly, with values ​​of the base current transfer coefficient of transistor T2 above 20, the error will be less than 5%, which is quite acceptable for amateur radio purposes (we are not launching the Shuttle to Venus).

Secondly, if we do launch the Shuttle and we need high accuracy, this error can easily be taken into account in the calculations. The emitter current of transistor T1 is almost equal to the base current of transistor T2, and this is what we will measure. As a result, when calculating h21e (and this is very convenient to do in Excel), instead of the formula: h21e=Ie/Ib, you need to use the formula: h21e=Ie/Ib-1

To minimize this error, as well as to ensure normal operation of the TL431 microcircuit in a wide range of currents, a transistor with maximum h21e. Since this is a low-power bipolar transistor, until our device is ready, you can use a Chinese multimeter. I managed to find an instance with a value of 250 out of only 5 KT3102 transistors.

Since today in the household of any radio amateur there is a Chinese multimeter(or even more than one), we will use it as a base current meter, which will allow us not to fence the switching for different ranges of base currents (I have a multimeter with automatic selection of the measurement limit), and at the same time exclude the rectifier bridge from the circuit – a digital multimeter does not care about the direction of the flowing current.

Scheme named after me, Siklai and Darlington.

To combine the above circuits into one, we will add some switching elements, a power supply, and for greater versatility, we will expand the range of emitter currents. The result was this:

Click to enlarge

With the ratings indicated in the diagram, the calculated emitter current is provided already at +4V supply voltage, so this is valid stable current generator. For the sake of experimentation, I connected transistors of the wrong structure a couple of times. Nothing burned! Although maybe it was worth asking more current? To be honest, few tests have been carried out on the endurance of this device, time will tell, but I like the beginning.

In principle, the device can be powered even from an unstabilized source, since current stabilization in the circuit is carried out over a very wide range of supply voltages. But! There are transistors (especially domestic ones) in which the base current transfer coefficient strongly depends on collector-emitter voltage. To eliminate measurement errors due to an unstable network, the circuit provides a stabilized power supply. By the way, it is precisely because of such “curves” of transistors that measurements should be carried out at at least three different current values.

So, circuit diagram of a device for testing transistors It turned out to be very simple, which allows you to easily assemble this device yourself, with your own hands. The device allows you to measure base current transfer coefficient low-power and high-power bipolar transistors “p-n-p” and “n-p-n” structures by measuring the base current at a fixed emitter current.

For low-power bipolar transistors The selected emitter current values ​​are: 2mA, 5mA, 10mA.
For powerful bipolar transistors measurements are carried out at emitter currents: 50mA, 100mA, 500mA.
No one forbids testing medium power transistors at currents of 10mA, 50mA, 100mA. In general, there are a lot of options.
The values ​​of the emitter currents can be changed at your discretion by recalculating the corresponding current-setting resistor using the formula:

R= Uо/Iе ,

where Uo is the reference voltage of TL431 (2.5V), Ie is the required emitter current of the transistor under test.

ATTENTION: In nature there are TL431 microcircuits with reference voltage 1.2V(I don’t remember how the markings are different). In this case, the values ​​of all current-setting resistors indicated in the diagram must be recalculated!

Construction and details.

Due to the simplicity of the device, no printed circuit board was developed; all elements are soldered to the pins of switches and connectors. The entire structure can be assembled in a small case; everything will depend on the dimensions of the transformer and switches used.

When testing powerful bipolar transistors at high currents (100mA and 500mA), they must be secured on the radiator! If a plate radiator is mounted on one of the walls of the device or the radiator itself is used as a wall of the device, this will make using the device more convenient. A radiator that is always with you! This will significantly speed up the process of testing powerful transistors in TO220, TO126, TOP3, TO247 and similar packages.

The power supply stabilizer chip also needs to be installed on a small radiator. Any diode bridge is suitable for a current of 1A and higher. As a transformer, you can use a suitable small-sized one, with a power of 10 W or more with a secondary winding voltage of 10-14 V.

Optional: The device for testing transistors has sockets for connecting a second multimeter (included in the DC voltage measurement mode to a limit of 2-3V). I spotted this idea on one of the forums. This allows you to measure Ube of the transistor (if necessary, calculate the slope). This function is very convenient when selecting bipolar transistors of the same structure for PARALLEL connection in one arm of the amplifier output stage. If at the same current the voltages Ueb differ by no more than 60 mV, then such transistors can be connected in parallel WITHOUT emitter current equalizing resistors. Now do you understand why Accuphase amplifiers, where up to 16 transistors are connected in parallel in each arm in the output stage, cost so much money?

List of elements used:

Resistors:
R3 - 820 Ohm, 0.25W,
R4 - 1k2, 0.25W,
R5 - 510 Ohm, 0.25 W,
R6 - 260 Ohm, 0.25W
R7 - 5.1 Ohm, 5W (more is better),
R8 - 26 Ohm, 1 W,
R9 - 51 Ohm, 0.5W,
R10 - 1k8, 0.25 W.

Capacitors:

C1 - 100nF, 63V,
C2 - 1000uF, 35V,
C3 - 470uF, 25V

Switching:

S1 - switch type P2K or biscuits for three positions with two groups of contacts for closure,
S2 - P2K type switch, toggle switch or biscuit with one group of contacts for switching,
S3 - switch type P2K or biscuits for two positions with four groups of contacts for switching,
S4—momentary button,
S5 - power switch

Active elements:

T3 - transistor type KT3102 or any low-power n-p-n type with high gain,
D3 - TL431,
VR1 - integrated stabilizer 7812 (KR142EN8B),
LED1 - green LED,
BR1 is a diode bridge with a current of 1A.

Tr1 - transformer with a power of 10W or more, with a secondary winding voltage of 10-14V,
F1 - fuse 100mA...250mA,
terminals (suitable available) for connecting measuring instruments and the transistor under test.

Working with a transistor tester.

1. Connect a multimeter to the device, turned on in current measurement mode. If there is no “auto” mode, then select the limit in accordance with the type of transistors being tested. For low-power ones - microamps, for high-power bipolar transistors - milliamps. If you are not sure about the choice of mode, set the milliamps first; if the readings are low, switch the device to a lower limit.

2. If there is a need to select transistors with the same Ube, connect a second multimeter to the corresponding sockets of the device in voltage measurement mode to a limit of 2-3V.

3. Connect the device to the network and press the “On” button (S5).

4. With switch S3 we select the structure of the transistor under test “p-n-p” or “n-p-n”, and with switch S2 its type is low-power or high-power. Using switch S1 we set minimum emitter current value.

5. Connect the leads of the transistor under test to the corresponding sockets. Moreover, if the transistor is powerful, it should be mounted on the radiator.

6. Press the S4 “Measurement” button for 2-3 seconds. We read the multimeter readings and enter them into the table.

7. Using switch S1, set the next value of the emitter current and repeat step 6.

8. Upon completion of measurements, disconnect the transistor from the device, and the device from the network. In principle, paired transistors can be selected based on similar values ​​of the measured base current. If you need to calculate the h21e coefficient or create graphs, you should transfer the data to an Excel spreadsheet or similar.

9. We compare the obtained data in the table and select transistors with similar values.

Instead of an epilogue.

A few comments on low-power bipolar transistors (it’s not for nothing that I provided modes for them?).
For some reason, radio amateurs, when building amplifiers using transistors, pay the greatest attention (and then in the best case) to the selection of identical specimens for the final stage.

Meanwhile, at the amplifier input they most often use differential stages or less often two-stroke. At the same time, it is completely forgotten that in order to receive from the differential. cascade as well as from a push-pull one, to the maximum of all its wonderful properties, transistors in such a cascade should also be selected!

Moreover, to ensure the closest possible temperature conditions, it is better to glue the housings of the differential cascade transistors together (or press them together with a clamp), rather than spreading them on different sides of the board. The use of integrated transistor assemblies in the input stage eliminates these problems, but such assemblies are sometimes expensive or simply not available to radio amateurs.

Therefore, the selection of low-power transistors for the input stage remains an urgent task, and the proposed device for testing transistors can significantly facilitate this process. Moreover, one of the modes chosen for measurement, a current of 5 mA, is most often the quiescent current of the first stage. And at what current does the Chinese multimeter measure???

Happy creativity!

Editor-in-Chief of RadioGazeta.

It is advisable to have a tester for medium and high power transistors in the measuring laboratory of a radio amateur. It is especially necessary when selecting pairs of transistors for the final push-pull stages of audio amplifiers with a power of more than 0.25 W.

Using the proposed device, you can test the collector junction of a transistor for breakdown, measure the static current transfer coefficient h21e, and check the stability of the transistor. Tests are carried out when the transistor is turned on according to a circuit with a common emitter. The indicator is a milliammeter with a current of 1 mA. The power source is a rectifier that provides a constant voltage of 12 V at a current of up to 300 mA. The reverse current of the Irbo collector junction is not measured, since it can range from several microamps to 12...15 mA for different transistors, and this parameter has virtually no effect on the selection of pairs of transistors for operation in a power amplifier.

The schematic diagram of the device is shown in Fig. 1. The VT transistor being tested is connected to the terminals of the electrodes to the corresponding terminals of the device. Switch SA1 sets the structure of the transistor. In this case, a power source is connected to the transistor in a polarity corresponding to its structure. Next, the transistors are checked, observing the following order: check the collector junction for breakdown; set the base current Ib equal to 1 mA; measure the static current transfer coefficient h 21e

Measurements of these parameters of medium and high power transistors are illustrated by the circuits shown in Fig. 2.

The collector junction is tested by pressing the SB2 Breakdown button. In this case, resistor R4 and milliammeter RA1 are included in the collector circuit of the transistor being tested VT, the negative terminal of which is connected to the power source, and resistors Rl - R3 are connected in parallel to the collector junction (Fig. 2, a).

At this time, the sliders of the variable resistors R2 and R3 should be in the right (according to the diagram) position. The current flowing through the chain of resistors Rl - R3 does not exceed 50 μA, which practically does not affect the readings of the milliammeter. Resistor R4 limits the current through the milliammeter to 1 mA, thereby preventing its needle from going off scale in the event of a breakdown of the collector junction of the transistor.

Milliammeter readings of less than 1 mA indicate the serviceability of the collector junction, and if there is a breakdown, the milliammeter needle will always be set to the rightmost scale division. In the event of a break between the terminals of the collector and base electrodes, the device will only show the current passing through resistors Rl - R4.

The base current /b, equal to 1 mA, is set with resistors R3 Rough and R2 Precisely with the SB2 button pressed. In this case, an insignificant initial collector current flows through the milliammeter (Fig. 2, b) and a current flows through resistors Rl - R3, which, when measuring the coefficient h21e, will be the base current Ib of the transistor being tested.

The static current transfer coefficient is measured by pressing the SB4 h21e 300 button or, with a small numerical value of this parameter, the SB3 h21e 60 button. In this case, the button contacts connect the transistor emitter to the positive (or negative, if the transistor is of a p-p-p structure) conductor of the power source, and parallel to the milliammeter is a wire resistor R5 (or R6), expanding the measurement limit (Fig. 2, c). The collector current of the transistor being tested will approximately correspond to its static current transfer ratio. The error arising from simplifying the switching of device circuits does not affect the selection of pairs of transistors for the output stages of powerful AF amplifiers.

When testing transistors of the p-p-p structure, a milliammeter is connected to the circuit of its emitter,

The design of the device is arbitrary. Resistors R1 and R4 are type MLT-0.5, R2 and R3 are type SP-3. Resistors R5 and R6 are made from wire with high resistivity with a diameter of 0.4...0.5 mm. Switch SA1 - toggle switch TP1-2, push-button switches SB1 - SB4-KM2-1. Power-on indicator HL1 - switch lamp KM24-90 (24 Vx90 mA).

By selecting resistor R4 with the collector and base terminals short-circuited and the SB2 button pressed, the milliammeter needle is set as accurately as possible to the rightmost division of the scale.

To adjust the resistances of resistors R5 and R6, you will need a standard milliammeter for a current of 300...400 mA and variable wire resistors with a resistance of 51...62 and 240...300 Ohms. Connect in series a standard milliammeter, a transistor tester milliammeter, resistor R5 and a variable resistor of 51....62 Ohms. Having turned on the power source, use a variable resistor to set a current in the circuit equal to 300 mA, while simultaneously making sure that the milliammeter needle of the device does not go off scale. After this, by adjusting the resistance of resistor R5, the milliammeter needle of the device is set to the rightmost scale division. Then the variable resistor is replaced with a resistor with a resistance of 240...300 Ohms, resistor R5 with resistor R6, and in the same way the current in the circuit is set to 60 mA, and the milliammeter needle of the device is set to the far right mark of the scale.

When the SB4 button is pressed, the deviation of the tester's milliammeter needle to the full scale corresponds to the static current transfer coefficient of the transistor 300, when the SB3 button is pressed - 60.


An extremely simple but convenient device for selecting pairs of medium and high power silicon transistors with determination of the current transfer coefficient.

Background

In the manufacture of amateur designs, especially amplifiers, it is highly desirable that pairs of transistors, both of the same conductivity and complementary, have as close parameters as possible. All other things being equal, transistors selected for current transfer coefficient work better, especially in the era of fashion for amplifiers with shallow OOS or even without it. Modern industrial devices are too expensive and not designed for hobbyists, and old ones are ineffective. The transistor meters built into cheap digital testers are not suitable for this purpose at all, since they usually carry out measurements at a current of 1 mA and a voltage of 5 V. Searches on the Internet for a simple but functional design did not yield any results, so once again I have to do the selection “on my knees” I don’t want it anymore, I want comfort. I had to invent it myself. I hope that there will be people willing to repeat this design.
The scheme is extremely simple, but has several highlights. First- measurement at a fixed current of the emitter (in fact, the collector), and not the base (idea from the magazine “Radio”, taken from the Datagor forum). This made it possible to place the transistors in the same conditions and select the current mode in which these transistors will operate.

Second- the adjustable zener diode on the TL431 allows you to smoothly set the current; with conventional zener diodes this is impossible, and selecting the “zener diode + resistor” pairs in the emitter circuit would cause problems. The third is a two-channel circuit and separate sockets for P-N-P and N-P-N transistors, which simplifies switching and allows you to instantly compare an experienced pair and check identity by changing the supply voltage.

Settings

I think that this is not a coffee maker and a person who needs to select pairs of transistors should imagine their operating modes and the possibilities of changing them.

If the resistance of the resistor in the emitter circuit is 15 Ohms and the measurement current changes by a factor of 10, the parallel resistor should have a nominal value 9 times greater, i.e. 135 Ohms (select 130 Ohms from the available ones; greater accuracy is not needed). The total resistance of the resistors will be 13.5 ohms. (You can take 15 and 150 Ohm resistors and connect them alternately with a toggle switch, but I like continuity). Install a transistor in the socket and use a variable resistor to set the voltage on the emitter to 2.7 V (temporarily short-circuit the terminals for measuring the base current).
The setup is complete.

Measure the base current. The ratio of the emitter current to the base current will give the current transfer coefficient of the transistor (it would be more correct to subtract the base current from the emitter current and get the collector current, but the error is small). When replacing transistors, there is no need to turn off the power; during testing, I repeatedly made mistakes and turned on the transistors “the other way around,” the tester showed that the base current was zero, no more problems.

The device was made for a current of 200 mA and a K-E voltage of 2 V, which is why the choice of a nominal value of 15 Ohms was chosen. Naturally, if you want to set the current to 300 mA, the voltage at the emitter will be 4 V and to maintain the voltage K-E = 2 V, the supply voltage should be not 5, but 6 V.

You can make measurements at a current of 1 A, then the resistor should be 3 Ohms. When increasing the supply voltage to 8...10 V, it is better to increase the value of the resistor that limits the current through TL431 to 200 Ohms.
In short, if you want to significantly change the measurement parameters, you will have to change the values ​​of one or two resistors.

Compared to a “proprietary” device that takes measurements on a short pulse, this device allows you to warm up the transistor under test - this mode is closer to the operating mode.
Instead of the M-832, you can turn on a regular dial milliammeter (or dial avometer), calibrate the scale in units of current gain, a 1/10 mA device is suitable, it will show a gain from 20 to 200...400. But then it will be impossible to smoothly change the measurement current.

Possible modernization

1. Transistors of the KT814 type inserted into the sockets “look” with inscriptions from the user. To eliminate this, you need to mirror the printed circuit board design from right to left.

2. If the KB junction is broken, the zener diode TL431 will receive voltage without a limiting resistor. Therefore, questionable transistors must first be checked for short circuits using a tester ohmmeter. To protect the TL431, instead of a 100 kOhm resistor (it prevents the mode with the base being torn off, I installed it to be on the safe side) you can install a 100 Ohm resistor and connect it in series with the milliammeter.

3. When an increased supply voltage is supplied for a long time, the power on the ballast resistor TL431 exceeds the rated value. You have to manage to burn out the resistor, but if you have such talent, you can install it with a power of 0.5 W with a resistance of 200 Ohms.

I did not make these changes - I consider it unnecessary to make “foolproof” for myself in a circuit of one zener diode and several resistors.
The board is simply glued to a piece of foam with a rigid film. It looks unaesthetic, but it works, it suits me, as they say: “cheap, reliable and practical.”

It allows you to measure the static current transfer coefficient of transistors of both structures at different values ​​of the base current, as well as the initial collector current. Using this device, you can easily select pairs of transistors for the output stages of low-frequency amplifiers.

The current transfer coefficient is measured at base currents of 1, 3 and 10 mA, set respectively by buttons S1, S2 and S3 (see figure). The collector current is measured on the milliammeter scale PA1. The value of the static current transfer coefficient is calculated by dividing the collector current by the base current. The maximum measured value of the parameter h 213 is 300. If the transistor is broken or a significant current flows in its collector circuit, the indicator lamps H1 and H2 light up.

The transistor being tested is connected to the tester through one of the connectors X1-X3. Connectors X2, X3 are designed for connecting medium-power transistors - one or another of them is used depending on the location of the terminals on the transistor body. To connector X1 under-

Powerful transistors with flexible leads are switched on (but without plugs at the end). If the terminals of the transistor are rigid, or flexible with plugs at the end, or it is installed on a radiator, a corresponding plug with three insulated stranded conductors is inserted into connector X1, at the ends of which alligator clips are soldered - they are connected to the terminals of the transistor. Depending on the structure of the transistor being tested, switch S4 is set to the appropriate position.

Connector X1 - SG-3 (SG-5 is also possible), X2 and X3 are homemade made from a small-sized multi-pin connector (standard sockets for transistors are also suitable, of course). Push buttons S1-S3 - P2K, S4 - also P2K, but with fixation in the pressed position. Resistors - MLT-0.125 or MLT-0.25. Indicator lamps - МН2.5-0.15 (operating voltage 2.5 V, current consumption

0.15 A). Milliammeter RA 1 - for a total needle deflection current of 300 mA.

The test parts are housed in a housing made of organic glass. On the front wall of the case there are connectors X1-X3, switch S4, buttons S1, S3 and milliammeter PA1. The remaining parts (including the power supply) are mounted inside the case. A sheet of paper with a grid for marking the values ​​of the collector current depending on the base current is glued to the front panel. The top of the sheet is covered with thin organic glass. The grid is used when constructing the characteristics of transistors, which are selected for the output stage of a low-frequency amplifier. The characteristics are drawn on the glass with a felt-tip pen or with a fountain pen and washed off with a damp swab.

Transistor testing begins with measuring the initial collector current with the base turned off. The PA1 milliammeter will show its value immediately after connecting the transistor leads to the connector. Then, by pressing the S1 button, the collector current is measured and the static current transfer coefficient is determined. If the collector current is small, switch to another range by pressing the S2 or S3 button.

Radio magazine, 1982, No. 9, p.49