In repair and amateur practice for quick check the health of high-frequency, low-frequency radio circuits and to detect faults in televisions, radios and other equipment, you can use the following devices.
A single transistor probe generator is designed for quick testing of cascades of amplifiers or radio receivers. circuit diagram probe generator is shown in fig. 1. It generates a pulsed voltage with an amplitude sufficient to test the pre-terminal and input stages of the amplification of low-frequency designs.
Rice. 1. Generator-probe on one transistor.
In addition to the fundamental frequency, the output of the probe will have a large number of harmonics, which allows it to be used to test high-frequency cascades - intermediate and high frequency amplifiers, local oscillators, and converters.
Generation occurs due to strong positive feedback between the collector and base circuits of the transistor. The signal taken from the base winding of the transformer Tr1 is fed through the capacitor C1 to the potentiometer R1, which regulates output voltage probe.
The transformer is wound on a small piece of ferrite rod. Winding I contains 2000 turns of PEL 0.07 wire, and winding II contains 400 turns of PEL 0.1 wire.
Transistor type MP39-MP42. Power battery - element "332" with a voltage of 1.5 V or a small-sized battery.
The probe is assembled in a small case (Fig. 1b). To connect to the chassis or common wire of the tested design, a flexible mounting wire with an alligator clip at the end is output.
A medical needle from a Record syringe is used as a metal probe. At the end of the case, a potentiometer is installed, on the handle of which there is a risk that allows you to judge the output signal.
Two-transistor probe generator without transformer
A probe generator on two transistors without a transformer generates rectangular pulses and allows you to check all stages of the amplifier or radio.
Rice. 2. Generator-probe on two transistors.
Moreover, the oscillation frequency can be changed by the capacitance of the capacitor C1: with an increase in capacitance, the frequency decreases. And a change in the resistance of the resistors affects the shape of the output oscillations: with an increase in R2 and a decrease in R3, it is easy to achieve sinusoidal oscillations at the output and thus turn the probe into sound generator with a fixed frequency. Transistors, battery and external design the same as in the probe generator on a single transistor.
The amateur radio probe-generator is designed to check the serviceability of high-frequency and low-frequency radio circuits of household equipment (radios, televisions, tape recorders). Schematic diagram of the probe is shown in fig. 3.
It is a multivibrator assembled on transistors T1, T2. The recorded signal is rectangular, the oscillation frequency is about 1000 Hz, the pulse amplitude is not less than 0.5 V. The generator probe is assembled in a plastic case, the length of the probe together with the needle is 166 mm, the case diameter is 18 mm.
Powered by one element "316" with a voltage of 1.5 V. To turn on the probe-generator, press the button and touch the tested cascade of the device with the tip of the probe. Cascades are recommended to be checked sequentially, starting from the input device.
Rice. 3. Probe-generator amateur radio.
If the cascade being tested is in good condition, a characteristic sound (speaker, telephone) or a strip (kinescope) will be heard at the output.
When checking devices that do not have a speaker or kinescope output, high-resistance headphones of the TON-2 type can serve as an indicator. It is strictly forbidden to check circuits with voltages above 250 V. When checking circuits, it is forbidden to touch the case of the device under test with your hands.
Small TV Troubleshooter
A small-sized device for detecting faults in TVs, radios and other household radio equipment by listening to the sound in the speaker of the device under test, observing the image on the TV screen, or connecting another indicator (voltmeter, headphones, oscilloscope, etc.) to the output of the device under test.
The device allows you to check in TVs: end-to-end channel, image channel, sound channel, synchronization circuits, vertical scanning linearity; in radio receivers: end-to-end path, UPCH channel, detector and ULF.
The device is a signal generator of complex shape. The low-frequency component of the signal has a repetition frequency of 200–850 Hz. The high-frequency component has a frequency of 5-7 MHz. The specified signal allows you to receive 2-20 horizontal stripes on the TV screen and sound in the speaker.
Rice. 4. Small-sized device for detecting faults in televisions.
The signal voltage at the output of the device is regulated by a potentiometer. The device is powered by a Krona-VTs battery. The consumed current is not more than 3 mA.
Overall dimensions of the device without a flexible output no more than 245 X X 35 X 28 mm. The length of the flexible outlet is at least 500 mm. The mass of the device is not more than 150 g.
The electrical circuit of the device is shown in fig. 4, a. The generator with intermittent excitation is made on a transistor T1 according to a common base circuit.
Intermittent excitation of the generator ensures the presence in the emitter circuit of the chain R3, C4. The signal at the emitter of transistor 77 is made up of intermittent high-frequency voltage and charge and discharge voltage of capacitor C4.
An emitter follower is made on the T2 transistor, which serves to increase the stability of the generator and reduce the input resistance of the device. The output level of the signal is adjusted using the potentiometer R5.
The body of the device is made in the form of two detachable covers made of impact-resistant polystyrene (Fig. 4.6). The covers are connected with a screw and a ferrule, which is also used to connect the instrument to the DUT. The case houses the device board and the Krona-VTs battery. The device is connected to the chassis of the device under test with a crocodile clip.
To determine the malfunction of the amplifying paths, the circuit is checked cascading, starting from the end of the tested path. To do this, a signal is applied to the input of the cascade by touching the tip of the device, while the absence of a signal on the indicator (TV screen, speaker, voltmeter, oscilloscope, headphones, etc.) will indicate a malfunction of the cascade.
To determine the nonlinearity of the image along the vertical, it is necessary: to obtain an image of horizontal stripes; measure the minimum and maximum distance between two adjacent lanes; determine the nonlinearity along the vertical by the formula:
where H is non-linearity, %; Imax is the maximum distance between the strips; Imnnnm - the minimum distance between the lanes. The stability of the image synchronization is judged by the stability of the horizontal stripes on the TV screen.
It should be borne in mind that the device is designed for connection to points of electrical circuits, the voltage of which does not exceed 250 V relative to the case. Voltage is the sum of constant and impulse voltage acting in the scheme.
Such a device will be very useful when testing the audio circuits of amplifiers of receivers, TVs and other industrial and home-made equipment. The generator circuit is given according to the book by V. G. Borisov “ Young radio amateur(from 145-146 in the 8th edition), with minor changes.
AF generator circuit
The generator is assembled on a K155LA3 chip (K555LA3 can be used), which is 4 2I-NOT elements. The generator itself is formed by series-connected logic elements DD1.1, DD1.2, DD1.3, connected by inverters. Capacitor C1, with a capacity of 0.47 uF, creates a positive feedback between the output DD1.2 and the input DD1.1. In principle, the signal can be taken from the output of DD1.3, element DD1.4 simply inverts them. The pulse frequency can be changed with a variable resistor R1. Resistor R2 serves as an output level regulator. Resistor resistance R1 680 Ohm, R2 10 kOhm, variable resistors can be of any type. With the parameters of the radio components indicated in the diagram, the pulse frequency can be changed within 500 - 5000 Hz. Diode VD1 serves to protect against power supply of the wrong polarity; any low-power diode, for example D220, is suitable as it. The circuit is mounted on a small breadboard. But due to the small number of parts, it is possible to carry out the scheme by surface mounting.
Complete generator
The nominal supply voltage of the K155 and K555 microcircuits is 5 V, but the generator is operable when the circuit is powered by a 4.5 V “square” battery (3336 type battery according to the old nomenclature), the voltage drop across the VD1 diode does not affect the operation of the device. The device can be used to test the operation of amplifiers audio frequency.
Every man to his own taste. As for sounds, mankind has also decided and well endows writers and extractors of musical amenities with benefits. Hearing is not developed by everyone, but no one has any doubts about the universal innate ability to publish something unpleasant for others, although this is a delusion.
The proposed Generator of Terrible Sounds (GUS) "turns on" children at the age of 4 ... 12 years. The impudently destructive meaning of the game is to select the most dissonant combination of frequencies.
The combination of several frequencies can always be assessed on a scale of excellent - terrible. The development of any perception is determined by its working range. Refined aesthetes and connoisseurs of toilet folklore are equally boring in communication. Sweet and savory lovers are lost to cooking. And what your dog thinks about the great French perfumery is better not to translate from a dog.
From the experience of coexistence with the GUS.
This is a sport: the purpose of the competition has no practical meaning.
It's a game: even if it's nerves.
This creativity: it takes talent, or at least ability, to win.
This is work: skill is developed.
This is pedagogy and the last will be first.
This is rest: for the mind and body, as they are not required.
This is science: maxinusity has not yet been found.
This mess: it ends at the same time as the batteries.
With all the variety of approaches to the production of unpleasant sounds, they can be reduced to two block diagrams. In any case, there is a set of separate audio frequency generators, by selecting the frequencies of which the desired impression is achieved. Then you can either combine the signals from the outputs of the generators into one and use a common amplification and sound reproduction channel, or each of the generators has its own amplifier and sound emitter.
A simple horror sound generator
Synthesizer
In the very simple case it is permissible to use simple pulse generators as individual sound generators. For collaboration, it is desirable to unify the characteristics of their output signals. Here they are meanders. A mixture of such signals somewhat improves the aural perception of their interacting harmonics.
Two oscillator channels are organized here, each of which consists of a frequency-tunable oscillator for logical elements and a frequency divider in half on a single-digit counter from the D-flip-flop. After such a divider, we always have a pure meander.
On the wiring diagram it can be seen that there are significant differences in the execution of functionally identical generators. This is a necessary measure when assembling them from a set of logic elements of one microcircuit package. Experience shows that for identical generators, when tuned to close frequencies, what is called frequency sticking, dragging, mutual synchronization occurs. Then the frequency regulator of one of them ceases to operate and copies the setting of the other in a large range.
If two generators have equal frequencies with significantly different values of the timing elements (here R2, PR1, C1 and R3, PR2, C2), then there is no such danger.
Although the microcircuits work well in the supply voltage range of 3.5 ... 15V, here they are powered through a parametric stabilizer (4.7V) on the VD1 reference diode. Its ballast are resistors R4, R5. Moreover, together with C3, they form a two-sided T-shaped noise filter.
The frequency of generators on logic elements is highly dependent on the supply voltage. In stand-alone devices, galvanic cells "sit down" over time, and without stabilization, the obtained infamy will improve.
The indicated input voltages +7.8...+10V correspond to a standard seven-cell galvanic battery of international size 6F22, known to us by its first (40 years ago!) name "Krona" or sealed cylindrical battery 7D-0.125.
If you have other sources of stable voltage, you can safely use them, excluding the elements VD1, R3 and R4. C3 is better left.
Acoustics
Horror is decorated with decibels. And scare himself, and generously share them with others. There are two ways. Either we use amplifiers and acoustics of existing household equipment, or we make a completely autonomous device.
The first way is simple, quick to perform, acoustically effective and ties a group of young experimenters to one place with a connecting cord, leaving the rest of the world for adults. The second way is good if adults are united by something stationary (table, TV, sofa), and everything that interferes is removed the farther beyond the horizon, the better.
In all music centers there are inputs for connecting external stereo sources (AUX). There are similar inputs on computer sound cards (AUX, LINE). All TVs are equipped with audio inputs (mostly monophonic so far). In all cases, the signal from one output is fed to the left channel, from the second to the right. Actually "horror" spatial separation of sounds does not interfere. Especially not up to the aesthetic experiences of the neighbors behind the wall.
The output level of pulse signals from the synthesizer is higher than required for a conventional low-frequency amplifier (Uinp = 0.2...1V, Rinp = 20...100kΩ), so there should be no problems with pairing. It is only necessary to remember that an alternating signal without a constant component must be applied to the ULF input, i.e. through a decoupling capacitor.
Pairing scheme for one channel. The RP5 trimmer matches the synthesizer's output level to the input level of a specific amplifier. Set it so that the amplifier's volume control controls it optimally.
An autonomous generator needs its own sound amplifier. We select them from the required output power. We combine the signals into one on a simple resistive mixer with the ability to separately adjust the output sound levels for each of the generator channels.
About setting
Frequency adjustment from low to high frequencies is carried out by changing the resistance of the tuning resistor. To get a comfortable feeling of a uniform change in frequency from the angle of rotation of the knob, its characteristic should be logarithmic. For domestic elements, it corresponds to the letter B at the end of the name. You can improve (complicate) the setting by dividing the sound range into two or three subranges.
For fair group play (much appreciated!) setting memory is essential. Even fixing just two settings is enough for flawless competition with any number of players in the Olympic system with the elimination of the loser. One of the settings stores the most impressive sound combination on this moment, and the second is used for the applicant's creative research. By moving the switch, you can always compare both sounds and choose the worst one. When a challenger wins, their settings are fixed, and the next attempt comes with the controls of the dethroned one.
Victory is desirable and should not be tempted by the opportunity to slightly tweak the sound of the leader. Settings need to be protected from smart people. In this case, the simplicity of the electronics leaves this function to the package designer. All options are suitable for mechanical blocking or difficulty accessing the controls of stored settings.
A good one has proven itself, for example, rod protection, where trimming resistors with a short slot are used as regulators, which do not protrude above the front panel of the device, and there is only one pair of rearrangeable recessed handles.
Horrible Sound Synthesizer. The case made of aluminum profile with side visors protects the handles well from accidental touches, and the location of the regulators related to different settings on opposite sides makes attempts to bring down the leader's settings very obvious. In the middle position of the A/B control switch, the power is removed.
Two settings in one of the generators. In the "off" switch position, a separate switch group SA1 (not shown) turns off the power.
Design
Synthesizer print layout. Power stabilizer (R3, R4, C3, VD1), required only in some cases, not shown. The tuning resistors RP1 and RP2 are installed separately.
Grid pitch 1.25 mm.
This article describes a simple audio frequency generator, in other words, a tweeter. The circuit is simple and consists of only 5 elements, except for the battery and the button.
Circuit description:
R1 sets the offset to the base VT1. And with the help of C1, Feedback. The speaker is the load VT2.
Assembly:
So, we need:
1) A complementary pair of 2 transistors, that is, one NPN and one PNP. Almost any low-power ones will do, for example KT315 and KT361. I used what was at hand - BC33740 and BC32740.
2) Capacitor 10-100nF, I used 47nF (marking 473).
3) Trimmer resistor about 100-200 kOhm
4) Any low power speaker. You can use headphones.
5) Battery. Almost any is possible. Finger, or crown, the difference will be only in the frequency of generation and power.
6) A small piece of foil fiberglass, if you plan to do everything on the board.
7) Button or toggle switch. I used a button from a Chinese laser pointer.
So. All details are collected. Let's start making the board. I made a simple surface mount board mechanically (i.e. using a cutter).
So, everything is ready for assembly.
First, we mount the main components.
Then we solder the power wires, a battery with a button and a speaker.
The video shows the operation of the circuit from a 1.5V battery. The tuning resistor changes the generation frequency
List of radio elements
| Designation | Type of | Denomination | Quantity | Note | Score | My notepad |
|---|---|---|---|---|---|---|
| VT1 | bipolar transistor | KT315B | 1 | To notepad | ||
| VT2 | bipolar transistor | KT361B | 1 | To notepad | ||
| C1 | Capacitor | 10-100nF | 1 | To notepad | ||
| R1 | Resistor | 1-200 kOhm | 1 |
They require a reference signal of a constant value during adjustment. Many experience and tune ULF circuits simply by touching the input with their finger or by filing musical melody from a PC or smartphone, more advanced hams run special test programs, but it would be best to assemble a small and simple low-noise test generator in order to solve this issue once and for all.
AF generator circuit for checking ULF
Transistor generator circuit for testing ULFThis circuit is a sine wave generator with three switchable frequencies: 300Hz, 1kHz, 3kHz, and due to the low harmonic distortion of 0.11%, 0.23% and 0.05% respectively at maximum output voltage, the device is really good works during tests and measurements of the parameters of amplifying audio devices.
Generator board for checking ULF The output voltage of the generator is set in 2 subranges 0 - 77.5 mV and 0 - 0.775 V (RMS). Frequencies are selected using switch S1, the output voltage range is S2.
Location of parts on the AF generator board Frequency calibration on each of the subranges is performed using a frequency meter and potentiometers R3, R4 and R5. Calibrate the output voltage with a millivoltmeter.
Output 1 waveform
Output 2 waveform
The circuit can be powered from 8 - 15 V. The 78L05 stabilizer with two 1N4148 diodes reduces the input voltage to 6.2 V. The current consumption is about 4.5 mA, therefore, in order to minimize noise and be able to use the tester autonomously, power it from batteries (accumulators ).