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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Powerful tube amplifier with multi-loop feedback. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Tube Power Amplifiers Main technical characteristics:
Parameters marked with * were measured by indirect methods and are approximate The schemes of the amps of E. Sergievsky (P90 / 2) and V. Kostin (P98 / 4) are taken as a basis. The main difference is the absence of electrolytes in the signal path and the coverage of individual cascades by local OOS, which made it possible to reduce the depth of the overall OOS and thereby increase the stability of the amplifier. Proper correction of feedback circuits and the use of filters at the input that limit the bandwidth contribute to the complete elimination of dynamic intermodulation distortion and determine the aperiodic response to a single impact and a delta pulse. The use of GU-50 lamps in the output stage, which are more linear than 6P41S and 6P45S, in a triode connection, made it possible to reduce the distortions created by the cascade by 2-3 times without the use of a time-consuming ultralinear circuit to set up. It is advisable to use lamps selected according to the characteristics. As a rule, lamps that have passed military acceptance, taken from the same series and from the same package, have a spread of no more than 1-2%, but it is still better to check this. In the pre-terminal cascade, 6N6P-I lamps are used, from the ZIP of the R-404 radio relay station, which have higher dynamic characteristics and higher allowable currents than conventional 6N6P. It is a good idea to check the identity of both triodes of the lamp by including them in a bridge circuit and measuring the unbalance of the bridge at various grid voltages. In the cathode circuit of the lamps of the pre-terminal stage, a current source is switched on on a 6Zh9P (6Zh52P) lamp. If possible, it is better to use the "iron" pentode 6Zh3 from aviation technology, which is characterized by greater stability of parameters. To improve the dynamic properties, you can try to assemble a pre-terminal cascade on a 6N5S lamp or a selected 6N19S pair, while a more powerful pentode should be used in the current generator, for example 6P1P, 6P14P and the like, but I didn’t have these lamps, and I have this option did not experience. Lamps 6N1P, 6N2P, 6N3P, 6N23P, 6N8S can be used in a phase inverter, while the main condition is the identity of both lamp triodes. The 6N8S and 6N8M lamps that have passed aviation acceptance have the highest linearity. It is also desirable to use them in a cathode follower. In the output transformer, it is desirable to use high-quality cold-rolled steel with a thickness of 0.35 mm; steel of a thinner thickness cannot be recommended, since the commensurability of the non-magnetic gap and the thickness of the tape contributes to the appearance of higher "tooth" harmonics. Despite the advantages of E-shaped cores, it is undesirable to use them in output trances due to the impossibility of accurate assembly at home. As a winding wire, PET-200 wire is used, which is supposedly made of oxygen-free copper (according to some sources from the Internet). The halves of the core are glued together with epoxy resin, to which finely dispersed ferrite powder with a permeability of 2000 is added (you can cook it in a regular coffee grinder, if you don’t feel sorry for it). It is advisable to impregnate the finished trance with epoxy to reduce magnetostriction losses (what a word!), Then place it in a screen made of thick permalloy (the thicker, the better, if you can then raise such an amplifier, I used 2mm permalloy) and fill it with sealant. The farther the trance core is from the walls of the screen, the better. If you have a lot of money, you can order a round armor core made of amorphous iron, since the companies involved in this business are now in bulk, in principle, the quality should get better, but I haven’t tried it, the salary doesn’t allow, and I don’t have cronyism in these companies. The amplifier is mounted on a fluoroplastic board 5 mm thick, with an oxygen-free copper wire (Phoenix, two-core, for acoustic systems, price 50 rubles / m). All resistors S2-29, wire SP5-3, it is advisable to measure their resistance after tuning and replace them with constant ones, K78-4 polypropylene capacitors and K71-8 polystyrene ones. It is highly undesirable to use metal paper and mica conders, despite all kinds of recommendations from audio maniacs, these conders have high absorption and significant leakage. To reduce the influence of the non-linearity of the contacts, the lamps are directly soldered into the circuit. The wiring of the common wire is shown in the diagram, and is carried out with a PPI-Uu wire with a core diameter of 3,15 mm (also sort of like oxygen-free copper), whoever has the money can use a branded cable with a finger thickness or branded OFS or Ag tires for wiring . Each channel of the amplifier is powered by a separate power supply. I don’t give a scheme, anyone can develop it, I’ll dwell only on some important points. All supply voltages are stabilized. Each voltage is taken from a separate winding. MOSFET transistors are used in stabilizers. The glow of the lamps is best fed from a current source separate for each lamp. If this seems too expensive, you can use a single source of constant voltage, but always with a smooth increase in the output voltage when turned on. It would be useful to recall that even a small shortfall of the output pentodes leads to their rapid failure. Also, in the power supply, a delay in the supply of anode voltages for 1-2 minutes after the amplifier is turned on should be provided. I used a time relay on the K1006VI1 timer, for switching I used the REP-17 relay with silver contacts, connected before the stabilizers. Rewound TCA-270 from TVs were used as power transformers. Power trances are shielded with a double screen, the first one, which is closer to the core, is made of electrical steel 2 mm thick, the second is made of permalloy 5 mm thick (what it was, and used it). To protect against interference from the network, a two-stage common mode filter and varistors are used. The glow of each lamp was powered by a separate current source on the IRF120, the anode stabilizers use the IRF830, the negative voltage stabilizers 2SJ117. At the output of the stabilizer + 420V there is an electrolyte 820mkX450V, parallel to it are 6 conders K78-17 10mkX450V. The amplifier is tuned according to the generally accepted method and consists in setting the desired lamp mode with variable resistors (6N6P bias of about -2 V, GU-50 of about -50V) and selecting corrective capacitors C3 and C5 to obtain the most even frequency response and phase response, if the transient response is If a resonant surge is observed, you can try to shunt the secondary winding of the output trance with an RC circuit with an appropriate time constant. If you have any difficulties in setting up, write to me, I will try to answer, my e-mail: arietz@chuvsu.ru Author: Kochkurov M.M.
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Comments on the article: Jury Tell me, please, is it possible to repeat this amplifier in stereo version? [roll] Jury Who followed this pattern?
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