|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Ekron is a tube amplifier with shielding grid control. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Audio equipment The authors introduce readers to the original circuit of a push-pull tube amplifier, in which phase inversion in one of the arms occurs using a screening grid as a control one. Relatively powerful output stage lamps (6P3S or G-807) are also controlled by shielding grids. In such an amplifier, the maximum output power reaches 20 ... 30 watts. A push-pull audio frequency power amplifier (UMZCH) is relatively simple, practically does not require adjustment and can develop a maximum output power of up to 20 ... 30 W per channel. An interesting feature of the amplifier is a phase inverter that rotates the phase of the signal with control over the screening grid. UMZCH due to the linearity of the characteristics can be used to listen and evaluate the quality of musical works at home and in the studio. The functional diagram of a phase inverter based on tetrodes (or pentodes) is shown in fig. 1. The VL1 shield grid has an amplified signal variable that can be used to drive another VL2 lamp through the shield grid to boost and invert the signal.
On fig. 2 shows a schematic diagram of one channel of a push-pull UMZCH.
The amplifier driver stage circuit differs little from traditional circuits of this type (the so-called SRPP structure, often performed on identical triodes), with the difference that pentodes (VL1.1, VL2.1) are used instead of the lower triodes, and their second grids are adapted to operation in phase inverter mode. Triodes VL1.2 and VL2.2 serve as a dynamically controlled load of pentodes. The output stage, like the inverting arm of the driver, works with second grid control, and the cathodes of the input and output lamps are directly connected to a common wire. Let us describe the operation of the amplifier stages in more detail. The input signal is fed to the control grid of the VL1.1 pentode and amplified by it. The second grids of pentodes VL1.1 and VL2.1 are connected through resistors R4 and R5 to the arms of the phase inverter and to each other through the capacitor C3, which are both the load and the dynamic voltage boost of the indicated shielding grids. In turn, the signal from the screening grid of the pentode part VL1 is fed through the capacitor C3 to the screening grid of the pentode VL2.1, amplified and inverted by it. Thus, the capacitor C3 is intended both for decoupling the arms for direct current, and for the normal operation of the pentodes. Pentode cathodes VL1. 1 and VL2.1 are connected to a common wire (the lamps operate with a small grid current), this helps to reduce the background and noise of the amplifier. The resistances of resistors R4 and R5 are chosen to provide the maximum voltage gain, and the resistance of resistors R3 and R6 is chosen to provide the necessary quiescent current for the output tetrodes VL3 and VL4. From the output of the phase inverter, the signal goes to the shielding grids of the lamps of the output stage, where the constant component of the voltage has such a value that it does not require additional bias. This allows you to abandon the cathode resistors and increase the efficiency of the amplifier. From the anodes of the VL3 and VL4 lamps, the power-amplified signal through the output transformer enters the load (loudspeaker). Below are the parameters of the UMZCH with 6P3S lamps. Main Specifications
The table shows the possible types and modes of the output stage lamps and the amplifier parameters achieved with them. Table
The amplifier does not actually need to be adjusted, except in cases where the output tetrodes have a significant spread of parameters. Then, in order to maintain the nominal level of non-linear distortion, the resistance of the resistor R5 is selected within a small range, achieving uniform limitation with an increase in the input sinusoidal signal. The radio elements of the amplifier, with the exception of the power supply and the variable resistor R1, are placed on the printed circuit board. The UMZCH printed circuit board can be made of foil fiberglass 1,5 mm thick. The amplifier uses surface-mounted lamp panels, which generally have the same mounting dimensions, unlike PCB lamp panels. There is no PCB lamp panel option for the G-807 lamp. On fig. 4 and fig. 5 shows drawings of printed circuit boards from the side of conductors and radio elements. Small printed circuit board (Fig. 4) - 120x120 mm in size, designed for 6P3S lamps; large - with dimensions of 200x160 mm (Fig. 5 - on a scale of M1: 2), designed for G807 lamps.
On the printed circuit board, the pads for desoldering the outputs of the lamp panels received the corresponding designations: for example, VL1 / 7 is the seventh output of the VL1 lamp. Lamp panels are installed on the board from the side of the printed conductors. The wires to the anodes of the output lamps are passed through holes in the PCB and soldered directly to the lamp panels (or to the anode terminal cap). The wires of the filament circuit are soldered in the same way, only they are twisted in pairs. The arrangement of printed conductors and radioelements, the laying and desoldering of wires make it possible to minimize parasitic capacitances and interference. Note that, subject to the lamp pinout, G-807 lamps can be installed on a small board, and 6P3S lamps on a large board. In the smoothing filters of each channel of the UMZCH power supply, either chokes or resistors with a resistance of about 200 ohms (with a power of 10 W) can be used. The low-frequency background level depends on the capacitance of the capacitors in the filters, we recommend installing oxide capacitors with a capacity of 220 μF for a voltage of 450 V (two for each channel), for example, K50-27, ECAP (Epcos). The design uses fixed resistors MLT-0,5 with a tolerance of ±10%, except for resistors R4 and R5 (with a tolerance of ±5%). Capacitors in positions C1 and C4 are preferably used for a rated voltage of 400 V, regardless of type; capacitors C2, C5 - film or ceramic. Capacitor C3 - K73-16 for a voltage of 160 V. The output transformer T1 is made on the magnetic circuit from the network transformer TSA-70-1 (PL22x32); it has two coils. The primary winding I with a wire with a diameter of 0,23 mm in each coil has five sections connected in series - a total of 1800 turns (in two layers of each section 360 turns). The secondary winding II in each coil has 141 turns of wire with a diameter (with insulation) of 0,35 mm, on each coil there are four single-layer sections in parallel. Alternation of winding sections in the following order: I-II-I-II-I-II-I-II-I. Connection of secondary windings - parallel, phasing is obligatory. Between the layers of the winding - 0,05 mm tracing paper, and between the sections - two layers of tracing paper. To minimize non-linear distortion, you can pre-select lamps with the same quiescent current. However, the amplifier works quite linearly and without selection. An experimental evaluation of the output resistance of the proposed UMZCH was carried out at a signal level close to the nominal power at a load resistance of 16 and 8 ohms. On the chart in Fig. 6 shows the frequency dependence of the output impedance of the amplifier.
The sound quality with an amplifier was evaluated using speakers in closed cases (from one to three bands) with dynamic heads 10GD-36K, Peerless, etc. The best effect is noted with English-made KEF Calinda speakers with passive radiators, as well as speakers with legendary French wideband heads Audax. It should be noted that we did not use speakers with a phase inverter and an open type. The terms "evenness" and "naturalness" are rather associated not with the speakers, but with the linearity of the UMZCH, which, however, we do not elevate to the rank of an absolute, but are looking for our circuitry and sound compromises. We used control by screening grids in order not to adjust the operation of control grids to the current mode of the less "compliant" second grids. The sound with UMZCH based on output stages with control over the first grid is subjectively perceived by some as more lively and dynamic in comparison with UMZCH with control over screening grids. Nevertheless, the advantage of the proposed amplifier is the "monitor", neutral nature of the sound, due to which, we hope, such circuitry can find its application and its connoisseurs. In conclusion, we note that the evenness and naturalness of the musical picture, achieved with this UMZCH, are, in our opinion, a consequence of the principle used to control the anode current. Authors: S. Akhmatov, V. Krayushkin, D. Sannikov
Machine for thinning flowers in gardens
02.05.2024 Advanced Infrared Microscope
02.05.2024 Air trap for insects
01.05.2024
▪ Triple Differential Receiver AD814 ▪ Neurolink - mini brain implant ▪ Camera with microlenses mimics eagle vision
▪ section of the site Stories from the life of radio amateurs. Selection of articles ▪ article Take it, take it, or even dirty your claws! Popular expression ▪ article Highlander mountain. Legends, cultivation, methods of application ▪ article Relay voltage stabilizer. Encyclopedia of radio electronics and electrical engineering
Comments on the article: Denis Tell me, please, did anyone collect it? alphamasyanya I found the necessary tips for adjusting the ULF. THANK YOU Nicholas I liked the amplifier design. And, which rarely happens, a complete and very good description.
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page