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1 Manufacturing of a 2.8-3.3 MHz transmitter with amplitude modulation on a protective grid. To drive three GU 50 lamps into the control grid, you need from 50 to 100 V RF voltage, with a power of no more than 1 W. And for pumping “to the cathode” - already tens of watts. It was necessary to decide on the “pathogen” scheme. The prototype of the “pathogen” was made according to scheme diagram 1. It produced an “honest” 10W without much effort. But this power is clearly in excess to drive three GU 50 lamps into the control grid. When the supply voltage was reduced to 12V, the power dropped to 5W. During the experiment, a generator was also tested according to scheme diagrams 2 and 3. On the emitter of the generator transistor in this version, the voltage diagram was somewhat more beautiful, but this did not affect the final result in any way.
2 I present diagrams of stress at point A. Diagram “a” refers to diagram 1. Diagram “b” and “c” refers to diagram 2. Diagram “b” was obtained by reducing C5 to 180Pf. It was decided to make “EXITITOR” according to diagram 3. Transistors can be used at any RF of low and medium power. Tr1 and Tr2 are wound on ferrite rings with an outer diameter of 10-12 mm with a permeability of 1000 or more. The windings contain turns of homemade twisted “three” and “five”. Transformers are made in the usual way: we wind a twisted (lightly, 1 turn per cm) bundle of PEL wire turn to turn, evenly distributing the winding around the circumference of the ring. Then in Tr1 the primary winding is made of two “lines” connected in series, the secondary is single, in Tr2 the primary is single, and the secondary winding is made of four (for a purely AM transmitter of two or three) serial “lines”. On the secondary winding (when all four lines are turned on) of the output stage, an RF voltage amplitude of up to 120V develops (the varnish insulation of the wires must be “correct”) at a load of 820 Ohms at a local oscillator consumption current of 1A. This is clearly a lot of power. Therefore, the output stage must be configured for a load of approximately 2.7..3K. By adjusting the current consumption of T3 with resistor R8, it is necessary to obtain the amplitude of the output voltage V. My resistance of resistor R8 was 1 1.3K. With a circuit supply voltage of 9 to 12V, the TOTAL current consumption was 150-
3 250mA. Below are oscillograms of voltages across the load. In the final version, elements numbered R8, D4, C12 (sch.2) were removed, and the beginning of the secondary winding TP1 was connected to “MACE”.
4 From them it is clear that it is quite possible to “start” the lamps both in class “B” for an AM transmitter (two (three) serial lines in Tr2 are used in the secondary winding) and in class “C” (all four serial lines in Tr2 are used in the secondary winding). Due to the fact that the output stage provides excess power, there was a temptation to use only the pre-final stage on T2 with transformer Tr2. But it was not possible to obtain more than 20V amplitude at a 2K load. Those who are not satisfied with the shape of the signal from the generator driver should make an “exciter” according to a scheme where the second and third stages operate in economical class C, and the output has a sinusoid, but the amplitude is already thirty percent less. I ended up using it so as not to force the lamp modes. Power supply The power supply of the transmitter is without any special features, it is made on a TS-270 transformer. It is installed on the chassis through shock-absorbing rubber washers. The chokes are used from old tube TVs. The diodes in the rectifiers are any rectifier type, for a current of 1-3A and a reverse voltage of 600V. All of them must be bypassed with capacitors. Transmitter output stage. The output stage of the transmitter is built on three GU50 lamps operating in class “B” and one 6P15P as a modulator with an inductive load. You don’t have to “unsolder” the limiter if you are not in the habit of shouting very loudly into a microphone, or you can adjust it to suit your speech characteristics by adding one more - two cells of back-to-back diodes (any low-power rectifier). Modulation is carried out on the protective grid GU50. There are no special features in such a circuit solution; therefore, a detailed explanatory text is not required. It can also be added that the anode choke can have any design, as long as the inductance is at least 1200 μH, this is due to the fact that the π circuit is designed for a high-resistance load, approximately 4.6K, since it is supposed to “power” the antenna at “half a wavelength” in one of its ends (started). Grid choke no less than 500 mcg. The whole “vegetable garden”, with fixed biases and chokes, was done on the assumption that the quiescent current would be set for each lamp separately, but in practice it turned out that this gives little. Therefore, a fixed Negative offset may not be
5 do, but combine all the control grids and ground them through a 30K..40K auto bias resistor. The π circuit data is calculated independently, depending on the frequency range and the antenna used. (The equivalent output resistance of one GU50 lamp is 4600 Ohms. Three, respectively, 1533 Ohms).
6 Transmitter automation Switching the transmitter to the “RECEIVING” mode occurs simultaneously by removing the excitation, that is, turning off the local oscillator power supply and de-energizing the power supply rectifiers of the transmitter power section. Microphone amplifier The microphone amplifier-compressor is made on a microcircuit “torn out” from a DVD set-top box (from the “karaoke” microphone path) and two transistors. It “gives out” the “positioned” ones into the 6P15P grid
7 2..2.5V LF amplitude. For fans of modulation “in the foreground”, the amplitude level can be raised to 5V using trimming resistor R10. There is also a control button in the microphone body, through which voltage is supplied to the power circuit of the transmitter control relay. This button is also duplicated by the “right-right” toggle switch. on the front panel of the transmitter. I used both electret and dynamic microphones, they work well, naturally each with its own frequency spectrum. Another version of the MU with a dynamic microphone. and my most “favorite” MU option: The design of the transmitter must meet the usual requirements for the layout and installation of powerful RF devices. The circuit design of the transmitter has the right to its own life, but the practice of its implementation
8 showed that it is much simpler and clearer to build such a transmitter entirely using tubes, well, maybe with the exception of a microphone amplifier. Then the power supply will be simpler and there will be fewer ambiguities in understanding the setup process. I would also like to note that the “protective grid” modulation method is good, correspondents note a “clean, neat signal,” but in terms of “assertiveness” and “arrogance” it is still inferior to the proven modulation to the screen grid via a cathode follower. The simplicity of the solution - to “power” a high-resistance antenna directly from the output of the pi circuit, is fraught with unpredictable “HF interference” to the low-signal paths of the transmitter. Therefore, if you want such “simplicity”, then you need to take care of the normal shielding of the low-signal path of the transmitter and eliminating the paths for the formation of a multiplicative background. This is due to the fact that the antenna has a very high input resistance, and the output stage, trying to “push” the “RF power” out of itself, pushes it anywhere, and not only into the antenna. Any design that has a small capacitive (5-10 pF) connection with the Pi circuit and the initial section of the antenna fabric already successfully absorbs almost a quarter of the transmitter’s output power. And if RF interference gets into, say, the circuit of diode rectifiers not shunted by capacitors, then the diodes will work as mixers of the frequency of the RF signal and the frequency of the alternating mains voltage. From the above, we can conclude that it is more correct to “connect” half-wave antennas to the Pi circuit of the transmitter through a low-resistance feeder, “powering” them at the corresponding points of the antenna fabric.
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The circuits can be used in equipment of the 1.9 MHz amateur band, officially approved for operation on the air by registered radio amateurs, i.e. having permission to operate an amateur radio station and a call sign. Some technical solutions from these schemes can be used in the design of amateur radio transmitters, or you can simply be nostalgic for the past - after all, the “radio hooligan youth” is behind the shoulders of many radio amateurs and just radio lovers.
Figure 1 shows a diagram of the simplest transmitting medium-wave set-top box with AM modulation for a radio receiver. The set-top box uses a 6PCS radio tube, the maximum power dissipation at the anode of which is 20.5 W.
Instead of a 6PCS, you can use a 6P6S lamp (maximum power dissipation at the anode is 13.2 W) - they have the same pinout.
The oscillatory circuit L1С1 is connected between the anode of the lamp and the control grid. It provides positive feedback of the cascade - one of the conditions necessary for self-excitation of the generator. Power is supplied to the lamp anode through an oscillating circuit (via a tap in coil L1). Switch SA1 is used to turn the cascade on in transmit mode and turn it off in receive mode.
The supply voltage comes from the anode of the output lamp of the ULF receiver, therefore, when a signal from the microphone is applied to the input of the ULF receiver, amplitude modulation of the HF oscillations generated by the attachment occurs.
Coil L1 is made on an ebonite frame with a diameter of D-30 mm and contains 55 turns of PEL-0.8 wire (turn to turn) with a tap from the 25th turn, counting from the bottom (according to the diagram) output. This attachment worked well, but had one drawback - the tuning capacitor C1 was galvanically connected to the anode of the lamp (and this is unsafe!), so the tuning knob had to be made of a dielectric.
Somewhat later, I managed to find a “organ organ” circuit (Fig. 2), devoid of this drawback. In it, a circuit is connected between the control grid and the cathode of the lamp. Moreover, partial inclusion of the cathode into the circuit due to tapping in the coil is used. This scheme is safer, but delivers slightly less power to the antenna than the previous one. Application of variable capacitor C1. allows you to optimally match the I-NW circuit with the antenna.
In this circuit, the 6PZS radio tube can also be replaced with a 6P6S. Coil I is wound on a ceramic mandrel with a diameter of D-32mm with PEL-0.7 wire. Number of turns - 50 (winding - turn to turn with a tap from the middle).
In Fig. Figure 3 shows a diagram of another “organ organ”. In it, KPI C2 is galvanically connected to the body through coil L2. If the terminals of this capacitor are accidentally shorted to the housing, nothing dangerous will happen - the generation of the RF signal will just stop.
The output power of this attachment is greater than that of the previous one (about the same as that of the circuit in Fig. 1), because The oscillatory circuit L2-SZ is connected to the lamp anode circuit. Throttle L1 is enclosed in a screen. Coil L2 is wound on a plastic mandrel with a diameter of D-30 mm with PEL-0.8 wire and contains 50 turns of wire wound turn to turn. The tap is from the middle of the winding.
Another schematic diagram of the simplest transmitting attachment on a 6PZS (6P6S) radio tube is shown in Fig. 4.
This circuit differs from the previous ones by the presence of inductor L1 in the anode circuit of the lamp, which made it possible to connect the output circuit to the anode. In this case, the stators of variable capacitors C2 and C5 are connected to a “common” wire, which significantly increases the safety of the device and makes it easier to control the setting elements. Switch SA1 is included in the cathode circuit of the lamp, with which you can adjust the depth of positive feedback, which allows you to quite accurately select the required mode of operation of the cascade. Coil L3 with adjustable inductance allows you to match the resistance of the output circuit with the input impedance of the antenna. This is important because A piece of wire of arbitrary length is often used as an antenna. Coil L2 is wound on a ceramic mandrel with a diameter of D-40mm and has 40 turns of PEL-0.7 wire (winding - turn to turn, taps are evenly distributed along the entire length of the winding), L4 - on a ceramic mandrel with a diameter of D-35mm and has 50 turns of wire PEL-0.6. In the author's version, coil L1 (choke) has an inductance of 1 µH, L2 - 8 µH, L3 - 250 µH, L4 -16 µH. I suggest winding L1 on a ceramic frame with a diameter of D-18mm and a length of 95mm with PELIA-0.35 wire (130 turns). The first 15 turns (closest to the anode) should be discharged in increments of 1.5 mm, the rest of the winding - turn to turn. I recommend making coil L3 similarly to L4, but increasing the number of turns to 100 and making taps from it (11 taps - according to the number of contacts in the switching strip) in order to make it possible to change the inductance of the coil. The taps should be positioned evenly along the length of the coils - this will simplify its design and, at the same time, allow it to maintain its tuning functions.
Tuning to the frequency in this circuit is done using capacitor C2, and the capacitance of capacitor C5 is selected according to the maximum signal at the output, i.e. adjust the output circuit L4-C5 to resonance. This design of the circuit allows you to tune the output circuit not only to the fundamental frequency, but also to its harmonics (most often the third is used). In this way, it is possible to increase the stability of the frequency of the signal generated by the generator, because The local oscillator operates at a frequency three times lower than the frequency of the output signal.
Figure 5 shows a hurdy-gurdy circuit made using two 6PCS radio tubes (you can also use 6P6S tubes, but there is no point in this - it is better to use one 6PCS). This circuit provides a more powerful output signal (about twice that of a single tube circuit). The anodes of the lamps are partially included in the generator circuit to reduce the effect of shunting. In the author’s version, it is recommended to wind coils L1-L3 on one ceramic frame with a diameter of D-40mm. Coil L1 contains 32 turns of PEL-0.3 wire, L2 - 41 turns of PEL-0.4 wire, L3 - 58 turns of PEL-0.7 wire. All coils are wound turn to turn. I recommend reducing the number of turns of each coil by 60 percent, otherwise the generation frequency will move from the mid-wave range to the long-wave range. By adjusting the resistance of resistor R1, you can change the operating mode of the radio tubes.
Figure 6 shows a diagram of a transmitter using two radio tubes. The oscillatory circuit L1-C2 is included in the cathode circuits of the lamps. Coils L1 and L2 are wound on one ceramic frame D-20 mm: And contains 60 turns of PEL-0.3 wire, L2 - 30 turns of PEL-0.4 (winding both coils - turn to turn). 2-3 turns of mounting wire (in insulation) are wound on top of coil L2, the ends of which are connected to an incandescent light bulb with a voltage of 6.3 V and a current of 0.28 mA (from a flashlight). This simplest chain provides an indication of the presence of RF generation. In addition, a neon light bulb placed close to the coil can be used as an RF indicator. By the intensity of the lamp's glow, one can judge the change in output power when tuning the range or a change in the parameters of the antenna (for example, when tuning it). So, if, when tuning the antenna, the frequency approaches the resonant one, then the light bulb will glow weaker (by the minimum glow one can judge that the antenna is tuned to resonance with the frequency generated by the transmitter, since there is a maximum power take-off). If the antenna breaks, the light bulb will glow as brightly as possible, and if there is a short circuit in the antenna, it may go out completely (this depends on the magnitude of the connection between the output circuit and the antenna, which is determined by the capacitance of the variable capacitor C1). The power switch SA1 also serves as a “receive/transmit” switch.
Figure 7 shows a diagram of the transmitting attachment on the GU50 radio tube. A significant difference between this circuit and the previous ones is the increased output power. Amplitude modulation is carried out along the protective grid of the lamp. Using a variable capacitor C5, the set-top box is tuned to the selected frequency, and using a capacitor C1, the output impedance of the transmitter is matched with the input impedance of the antenna. We should not forget that in this circuit one of the plates of the variable capacitor C5 is under a voltage of 800 V, so be very careful and use a control knob made of high-quality dielectric material to adjust the capacitance of this capacitor.
Coil L1 is wound on a ceramic frame D-40 mm and contains 50 turns of PEL-0.7 wire (winding - turn to turn) with a tap from the middle.
Figure 8 shows another diagram of a transmitter made on a GU50 radio tube. In it, the generation frequency is set by the L1-C2 circuit, and at the output of the device the so-called P-circuit C7-L2-C8 is used, which makes it possible to very well match the output impedance of the cascade with the input impedance of the antenna. Using the variable capacitor C7, the P-circuit is tuned to resonance (the output resistance of the lamp is matched with the resistance of the P-circuit), and using C8, the coupling value with the antenna is selected. Amplitude modulation of the output signal is carried out along the protective grid of the lamp.
Chain C3-VD1-R2 are elements for protecting speaker circuits from RF interference. By selecting the resistance of the resistors (within 0.5-1 MOhm) and R3, you can select the optimal mode of operation of the lamp.
Coil L1 is wound on a cylindrical ceramic frame D-40 mm with PEL wire 0.9 and contains 60 turns, wound turn to turn. Coil L2 is wound on a ceramic frame D-50 mm and contains 70 turns of PEL wire with a diameter of 1.2-1.5 mm (winding - turn to turn). Anode choke L3 is wound on a ceramic frame D-12 mm. The original recommendation states that it contains 7 sections of 120 turns of PEL-0.4 wire wound in bulk, but most likely two sections of 120 turns are sufficient.
V.Rubtsov, UN7BV
Astana, Kazakhstan
- the GU-50 pentode was developed in Germany in the mid-30s and was codenamed LS50. This is an interesting and quite rare radio tube in our time, which was also produced in the Soviet Union. It is intended to amplify power and generate high-frequency oscillations. The lamp is very reliable in operation and can be said to be “unsinkable”. It’s not for nothing that there is a saying that the GU-50 can only be split or lost. This implies that it is quite difficult to spoil it with other actions. It was these qualities of the lamp that attracted the attention of army signalmen at one time.
Pentode LS50. An original copy from the Telefunken company, model 1942.
As soon as the LS50 lamp appeared, it was instantly copied by many of the world's manufacturers of vacuum devices, which indicates the enormous interest it aroused. Nevertheless, its production continues to this day.
Tube amplifier circuit for GU-50 It includes three transformers, two of which are output and one network. If you make them yourself, then for this you can use trans from UPSs for computers (uninterruptible power supply), or rather their hardware. To do this, you need to modernize them, remove the factory windings and wind your own with the required voltages. The finished output transformers should have the following parameters:
Cores Ш38х45. The primary winding contains 2800 turns of 0.25mm wire. Consists of three sections 700+1400+700 turns. Between them there are 2 sections of the secondary winding of 120 turns of 0.86 wire. The secondary windings are connected in parallel and have a tap from the 86th turn. Interlayer insulation – fax paper in one layer. The insulation between the primary and secondary windings is 3 layers of the same paper.
Ultimately, there will be a transformer capable of guaranteeing a load of 4.6 kOhm in the anode circuit of the lamp, as well as output paths for connecting acoustics with a resistance of 4 Ohms - 8 Ohms.
To assemble a pair of absolutely identical transformers, it is necessary to divide the magnetic circuit plates into equal parts. Then it is advisable to mix these plates. That is, so that when reassembling the cores, one part of the plates would be from one trans, the other from another. In this case, it will be possible to guarantee that both transformers will have exactly the same parametric characteristics.
After you have made the transformer, it should be soaked in paraffin. To do this, you need to place the structure in a container with molten paraffin for about 50 minutes or a little more, for good soaking.
The power transformer installed in the tube amplifier is implemented on a W-shaped magnetic circuit W40x40. To accurately calculate it, you need to use the simple PowerTrans v1.0 program. To ensure the most reliable operation of the transformer, after carrying out calculations in the program, you need to increase the cross-section of the wire for the primary winding by about 10%. The archive contains the program itself and a detailed reference book on winding wires and methods for manufacturing transformer coils. Download
The picture shows the program window with already calculated data for winding:
Tube amplifier circuit for GU-50 suggests that for use in an amplifier as a power transformer, you can practically take any one with a power consumption of around 150 W. Transformers from Soviet-made tube TVs, for example: TS-180 or TS-270, are well suited for this purpose. They are not very difficult to rewind. The secondary winding is removed and a new one is made with the voltages you need.
Tube amplifier circuit for GU-50 with its beam pentode, which performs the function of power amplification and also serves to generate high-frequency oscillations. The location of the radio lamp in the structure must be strictly vertical, that is, the lamp panel is at the bottom. The principle of its operation is as follows: a positive voltage of 255v is supplied to the circuit of the second grid. This voltage is taken from the anode terminal of the transformer. Then, through a rectifying diode, it enters the circuit assembled on a capacitor and inductor, and there the rectified voltage is smoothed out. This principle of operation of the GU-50 radio tube allows you to increase the power at the output of the tube amplifier.
The lamp bias is fixed. The negative voltage in the first grid circuit comes from the power supply from an individual rectifier. Potentiometers, with a special rod for a screwdriver to adjust the bias level, are installed on the top of the housing, immediately behind the lamps. This is done to facilitate access to setting the operating mode of the GU-50 without removing the top cover of the case.
On the front panel there are two dial indicators for monitoring the quiescent current of the lamps in the final stage. If the indicator arrow moves to the red sector, this means the power of the output radio tubes is overloaded.
There is nothing complicated about setting the bias voltage on the pentode. You just need to adjust the final stage using the potentiometer located under the slot on the top panel of the housing. When making adjustments, the indicator arrow should be in the area of the red segment of the scale. This entire procedure is especially required after replacing the output tube. In general, during the initial setup, you can measure the voltage with a multimeter on a resistor that is installed in the cathode circuit of the GU-50 radio tube. The operating quiescent current is set to 90 mA, after which you need to adjust the quenching resistor of the dial indicator so that the arrow is set to the value you need.
A constant resistor installed in the cathode circuit of the output stage has a nominal resistance of 10 Ohms. This makes it possible to extremely accurately set the operating mode of the cascade. This resistor also plays another role - it creates a small Negative Feedback. Using such OOS increases the stability of the final stage, it resists the possibility of excitation at high frequencies. This is why a wirewound resistor of class C5-5 and a power of 5 W is installed in the cathode circuit of the lamp. Actually, this resistor creates inductance, which means that at high frequencies the gain of the lamp is weakened.
Tube amplifier circuit for GU-50 in its preliminary stage it has a 6Zh4 pentode, which is switched on in triode mode and also has a fixed bias. This voltage offset is created by a low-power zener diode KS133A. If someone is not satisfied with this connection scheme, then you can use the CR2032 lithium battery that is in the PC. Or install a constant resistor with a nominal value of ≈360 Ohms in the cathode circuit, and then shunt it with a capacitance with a nominal value of 3000 μF.
The transmitter is based on the S9-1449-1800 synthesizer. At the output of the synthesizer, two 6P15P radio tubes with common grids are installed. The output transistors of the synthesizer switch them with rectangular current pulses alternately along the cathodes. The anodes of the lamps are connected together and loaded onto the oscillating circuit of the frequency doubler. Next, the signal is amplified by a GU-50 radio tube (the pumping power is enough to turn on two GU-50s in parallel, while the transmitter power can be almost doubled). A parallel oscillating circuit with a switchable multi-tap coupling coil and a complex matching circuit is installed in the anode of the lamp, allowing any type of antenna to be connected to the transmitter. The anode and screen circuits of the output lamps are powered through a modulation choke. A powerful transistor amplifier with a transformer output is used as a modulator. That is, there is a classic anode-screen modulation with a parallel voltage supply circuit. The output power of the transmitter in silent mode is 20 watts, when modulated by a sinusoidal signal (telephone power) - 30 W, at modulation peaks - up to 80 watts. This is enough to ensure reliable reception within a radius of up to 15 km in urban areas; for rural areas, the broadcast radius will be up to 30 kilometers. That is, this is a transmitter for most cities in Russia, or for the territories of small rural areas. It can also be successfully used as a regular transmitter for individual radio broadcasting of a technical school or institute radio club. It will also be good for a personal individual broadcasting station. However, since the transmitter contains high voltages of more than 1000 volts, it is permissible to assemble, set up and operate it only by persons over 18 years of age and under the supervision of an experienced radio engineer - the head of the radio circle.
This transmitter fully meets the quality standards for radio broadcast transmitters in accordance with GOST R 51742-2001.
The front panel of the transmitter contains:
On the back panel there are:
Dimensions of the transmitter chassis: 420×140×150 mm.
Housing dimensions (transmitter with power supply and modulator): 500×320×305 mm.
One of the stages of transmitter installation. On the left is a box-shaped compartment for the C9-1449-1800 synthesizer. Next, a summing frequency doubler section on two 6P15P with a circuit tuning capacitor. To the right is the output stage of the GU-50, the output circuit tuning capacitors and the antenna tuning capacitor are visible. In the foreground is the EM84 indicator.
One of the stages of transmitter installation. Chassis basement. On the left is a compartment of the antenna matching circuit; a toroidal extension coil and antenna-type switches are visible. Next, the anode compartment of the output stage, you can see: the anode choke, the output circuit coil with the coupling coil and the switch of the coupling coil turns with the antenna. To the right, the compartment of the grid circuits of the output stage and the anode circuits of the doubler, the toroidal coil of the doubler circuit is visible. Next, the grid circuit compartment of the doubler and the decoupler box compartment of the synthesizer.
While still students, we had fun by generating electromagnetic NE waves and modulated them in amplitude. Naturally illegal. To put it simply, we built it with a friend tube radio transmitters and aired them on NE band. But at that time tube receivers classical folk music has already begun to fade into oblivion prefix – hurdy-gurdy for 6p3s, connected to the sound cascade tube receiver was no longer relevant. That is, not having a tube receiver at home, to go on air, a full-fledged radio transmitter, not a prefix. Semiconductors were in short supply, but radio tubes there were rubble - it was full of dirt all around. And then my friend and I decided to do two tube transmitters- one of which is my copy, is still kept on my mezzanine as a relic and memory of those dark pre-computer times.
Young people then did not have the virtual world and social networks, but only a TV with two channels, a football ground, a bicycle, a tape recorder, and three sevens port wine. Standard set of entertainment of that time. I don't judge whether this is good or bad. It was just like that back then.
In the beginning, in fact, we built and tested one radio transmitter- my copy. The diagram was compiled by us from different parts of different sources and was constantly being reworked to fit the available parts. Parts were obtained from everywhere - exchanged, bought and begged from friends. For example power supply transformer was exchanged, as I remember now, for a new pump from a bicycle from one grandfather. Transmitter It was redesigned several times until it was finally finalized, optimized in terms of the number of parts and structurally designed on a wooden chassis.
Transmitter antenna served as a 10-meter wire suspended at a height of about 2 meters on insulators above the roof of a five-story building between two wire radio masts installed on the same roof. That is, the wire was located next to two standard radio broadcast wires, which seemed to mask the antenna. The descent was carried out with an antenna (television) cable, passed into the mast pipe and skillfully carried through the attic of the five-story building and the exhaust shaft directly into the apartment.
The transmitter operated at a frequency of about 1000 kHz. All this is of course conditional - according to the receiver’s arrow in the middle of the CB range. I conducted the reception on the radio " Selga 405" - mainly when transmitter testing. After 12 at night he turned on a tape recorder with music connected to transmitter and went out into the street with “Selga” hidden under his jacket. Listening was carried out using one earphone. And so I walked around the city at night, like a special agent on a secret mission - checking the range and quality of reception. My friend sometimes went with the same task, but in his own area - 1 km from me. To control the transmission quality longer - I slowed down the tape recorder motor. So the cassette playing time increased from 30 minutes to 1 hour. We were pleased with the test results. There was a reception in all parts of our area. True, it is much worse on the outskirts. Probably due to not very good antenna. Interference in those days on the NE band it was not enough - not like now, with the massive appearance of switching power supplies and other emitting crap. So basically our transmitter covered the planned area.
In general, after a series of tests, we then built second transmitter according to the completed sketches and diagrams. It differed from the first one in a 6p15p lamp in the modulator, a power transformer and some design details. Having achieved a coincidence of frequencies - made the first radio communication. We greeted each other on the air and began to take turns yelling like idiots into the microphones, “race - race, race two three, how can you hear the reception.” Scientifically, “adjusting the modulation depth” is called: -). And for some reason, then we didn’t care that we were sitting on the broadcast CB band and in broad daylight we were quacking like fools “all over Ivanovo” from our five-story buildings. Two unafraid idiots :-) . Of course, I wouldn’t allow myself that now. But then, it was cool!
All this fuss with building and testing the transmitter, together with frequent interruptions, took time - probably about a year.
The call sign of my transmitter was “Orion”, the call sign of my friend’s transmitter was “Impulse”. Later we played music after 12 at night. There were no “pro-life” conversations, just like every day as a student at a technical school.
Objectively speaking, at first it was very cool, but over time I quickly got tired of it. Actually myself the process of building a transmitter for the CB range turned out to be much more interesting than playing several dozen tape cassettes on air.
Then my friend went to study in another city, where he stayed. Mine transmitter he bequeathed it to his younger brother, a dunce, who immediately dismantled it into parts along the way. And I played the music a little more and abandoned the matter. But sometimes, I get it from the mezzanine transmitter and like in the good old days, after 12 at night I turn on music for half an hour, inserting the call sign “Orion” into the pauses.
This is a bit of a sad story two tube pirate radio transmitters on the CB broadcast band in one small county town.
Regarding the fact that we could have been “involved” by the relevant authorities: they could! But somehow it went unnoticed. Toli transmitter power is low, perhaps no one complained about interference, or interference They didn't really bother anyone. Another plus is that transmitter master oscillator made not according to the classic Sharman three-point scheme with a bunch of harmonics, but according to the “ GPD Shadsky" - an excellent circuit with a minimum of harmonics ( Radio magazine No. 1, 1963 Page 20). By the way, this is very clearly visible on the computer monitor screen - Receiver SDR. Really, when rebuilding the transmitter only one main peak runs across the range and only pair of harmonic peaks.
The transmitter power could be increased. Later, I had the idea to assemble an amplification stage - attachment on a 6p45 lamp according to the classic single-cycle circuit, but didn’t get around to it. Although, somehow for testing, I soldered with a surface-mounted installation additional stage on another one lamp 6p14p– I liked the result. Transmission range increased significantly. But for some reason it didn’t catch on - I was too lazy to improve this amplifier constructively. Although, in principle, it was possible - there would be room for 6p14p on the chassis.
An ULF, also known as a modulator, is assembled on lamp L1, L2. Basically UCH scheme Can be any other lamp.
A master oscillator (GPA) is assembled on lamp L3 smooth range generator) according to Shatsky's scheme. Just a wonderful circuit that produces one clear carrier peak and a couple of weak harmonics at the output. Compared to a three-point generator, it’s “heaven and earth.”
An output signal power amplifier is assembled on lamp L4.
L1 – Generator circuit coil, setting the transmitter frequency. 75-100 turns on the frame from the IF circuit of a USSR TV. The coil is in a standard aluminum screen. *2 standard ferrite cores are screwed into the coil - specifically for this transmitter.
Variable capacitor, connected in parallel L1 – adjustment of the transmitter according to the range (capacitor from transistor radio receiver).
Coil L2 – P circuit. 100 turns (depending on antennas).
