The small signal is looking for, two appliances, Signal Generator
Keywords: small signal is looking for, two appliance production
Here you introduce you to your teen friends, simple, small size (like pen), facilitating signals for carrying and use, using easy signals, using it, can easily look for and determine the speed of radio, recorder, megaphone, etc. The location.
I. Working principle
The signal is displayed, and the circuit of the two appliances occurs, as shown in FIG. 1, is composed of crystal triodes VT1, VT2, and the sealing element.
When used as a signal tracing, the jack XS needs to access an 8Ω low-resistance earplug machine. At this time, VT1 and Vt2 constitute a direct coupling amplifier, R1 as a bias resistor of the two tubes, and C1 as an input end interval DC capacitor. Since the operating point of VT1 is selected, it is in a curved portion of the amplified characteristic curve, so VT1 has a detection effect. Regardless of whether the high frequency or medium frequency amplitude amplitude wave signal is input between the probe and the ground clip, the amplified audio signal sound can be heard in the earphones. However, there is slight distortion when the low frequency signal is laid, but does not affect the actual use.
When used as a signal generator, the jack XS is empty. At this time, C2 is connected to the positive feedback capacitor of the circuit, so that the VT1 and VT2 constitute an audio self-excited multi-resmier, output an audio signal between the probe and the ground clip. Since the output waveform is approximately square wave, the high-end harmonic is very rich, and can extend from the audio to the high frequency range of dozens of megabo, so the signal generator can be used to overhaul the low frequency part of the audio device such as the radio, and available The maintenance intermediate frequency and high frequency section make it function to expand.
Second, the component selection
Transistor Vt1 is selected from the group consisting of 9011 or 3DG6, 3DG201 silicon NPN small power triode, VT2 selected from 9015 or 3 cg21 silicon PNP small power triode, and two tube current amplification coefficient β is preferably 40 to 100.
R1, R2 all use RTX-1 / 8W carbon film resistors. C1, C2 should be used in CJ10-400V and CJ10-250V-type metal-based paper-based capacitors, and both withstand voltage is selected, and the purpose is to be able to overhaul the exchange of electronic pipe harvests and megaphones. XS selection with CKX2-3.5 ordinary two-core jacks. G use the No. 5 (or 7) dry battery section, the voltage is 1.5V.
The probe is processed by a crude copper wire, and it can also be restructured by a large sewing needle to require a length of the jacket that is slightly shorter than the probe. The ground wire should be used in the commercially available quarter crocodile clip, the lead length is about 1m or so.
Third, production and use
Fig. 2 shows a printed circuit board soldering diagram of the apparatus, and the actual size of the printed circuit board is about 90 mm × 20 mm.
When making, the power switch SB is made according to FIG. The battery holders are bent into a "L" shape with two pieces of 15 mm × 7 mm phosphorus clands, and then welded directly on the printed circuit board. The entire circuit movement can be loaded into a size of φ25 mm × 95 mm plastic cylindrical, and its shape is shown in Figure 4.
Debugging is very simple: find a good semiconductor radio, tune it in the position of the radio broadcast; then, insert an 8Ω low-resistance earplug machine in the jack XS of the two utensils, clamp the two utensils in the radio The common ground terminal (generally the power supply negative terminal), with the probe contacts the high-frequency or intermediate frequency portions of the radio, such as the hot end (non-ground end) of the radio transformer in the radio, will listen in the earphones Go to the radio broadcast of the radio. Suitable change the resistance size of the resistor R1, so that the broadcast sounds hete up in the earplug is the most loud and clear. It is also possible to connect the top 10,000 menu (DC 10mA gear) at both ends of the SB, and test the working current of the two appliances, requiring between 3 and 5 mA. If the difference is too large, simply adjust the resistor R1 resistance to meet the requirements. When using, if you want to find a completely silent radio (or other audio device) fault, simply turn on the ground line clip on the public ground of the radio to be repaired, turn on the power supply of the radio, the rotary tuning capacitor is Place of radio broadcasts, starting from the front level of the radio to the post-level, sequentially contact the sponor from each solder joint, and the broadcast sound should be heard in the tracery's earphones. If you encounter a broadcast, you can't hear the broadcast, indicating that the fault is at this stage, which greatly reduces the scope of the fault judgment.
If used as a signal generator, the jack XS does not have to be plugged in, as long as the switch SB is pressed, the probe has signal output. The crocodile clip can be sandwiched on the common ground terminal of the radio (or acoustic device), and the base or collector of the radio transistor in the radio is sequentially touched by the probe from the rear stage. Both the speakers in the radio should have a loud "beep-" sound. If you feel silent when you touch a certain level, you will explain the fault at this level.
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