Super Priboj Clasa A

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   MODIFY Priboj FOR valve sound I did a find in a grocery store. Among the rubble behind the counter, I saw an old rörhäck the brand Priboj-50, which I managed to buy for 60,000 Rubles (about 200). Dragged it home, picked from the output transformers which I connected to a pair triodkopplade EL34's and said - Not bad at all. And so was born the idea to make something more of Pribojen. Thanks to its designer, Volodja Starodubtsev, has a pair of output transformers of extremely high quality. Anyway hemmapulare offered to pick up a new Priboj 50 UM 204 GB of parts from an old (including output tubes), and thus the opportunity to get their own arguments in the discussion of the tubes any excellence across the transistors. What then is to modify off transistor sound? I list the following elements: Ping Cup schedule must be made easier (in all things, including the number of components and wires). All components, including resistors, capacitors, connectors cables (and SOLDER!) Including also the power supply must be carefully selected to maximally harmonize with each other for good sound. The amplifier must not be motkopplad matter how small negative feedback than could possibly be. The output must be active and not dependent on the instantaneous value of the signal and not exceed half the nominal speaker impedance (this criterion only a triodförstärkare working in Class A). Each channel shall have a separate power supply to be able to provide power supply free from any interference and hum. (This is especially important for precisely triodförstärkare compared with pentodsteg) For entry into the two-stroke Paradise we have to make some sacrifices. When the pipes 6P3C triodkopplas and is in Class A lost about 3/4 of the possible output power. Therefore, regardless of softclipping by oversteer, DELIVERING NOT MODIFICATION OF YOUR SPEAKERS HAVE A SENSITIVITY LESS THAN 90dB/W/m!! According to the textbook, we have the following efficiencies for different amplifiers Pentode Class B -78% Triod Class B -35.3% Triod Class A -25% Unfortunately, these values are also theoretical because non-ideal anodkaraktäristika. For Pribojens 6P3C-pipes, we lack curves when the pipes are as triodes. Therefore we connect quickly up a tube to obtain the required parameters. We have in mind that the max anodförlust Pamax = 40W and maximum gallaerförspänning Ug2amax = 300V. Between the anode and screen grid is a resistance on 1Kohm. Taking up the parameters takes no longer than necessary. We are currently just the ratio Ia / Ua (anode current / grid power) at UG1 = 0 (at 0V grid voltage). See Figure 1. The major changes in the anode current relationship seems linear with a  slope equal to the pipe internal resistance Ri = (Ua / Ia) = 200ohm, and mild changes non-linearly (at Ia <0.05A). It increases the tube's internal resistance, thus limiting traction. The graph shows the ratio of the anode current and anodgaller (at UG1 = 0V) and limitations; maximum anodförlust Pamax, anodgallrets maximum voltage Ug2max and point selected, the minimum plate current Iamin. It remains an area in which we want the tubes will work - triode and Class A. If we allow an active anodlast (ie a cargo of hötalare, whose load transformed through the output transformers which anodlast, has a complex impedance. Deeming it as active, we are only in the first adoption of optimum impedance Ra = 2i - will trio markets to deliver its maximum power, so the gain of a signal, the load line (Figure 1 again) that is plotted as a line -1/Ra. I can calculate the maximum power taking into account the limit lines UG1 = 0 (with coordinates Uamin = 120.5 V and iamax = 0.325 A) and iamin = 0.05 A and UAmax = 299.5 V. We place the operating point in the middle of the useful part of the line -1/Ra with koordinarerena: UA0 = (UAmax + Uamin) / 2 = 210V Iamax = (iamax + iamin) / 0.186 A In a cascade, with the output transformer, the resting tension UA0, we can consider this as a voltage output by the power supply with a quiescent current ia0. To get this quiescent current, determined bias voltage on the control grids experimentally to UG1 =-15V. In a two-stroke amplifier bias voltage will be automatically balanced over the joint cathode resistor. Power calculation is done after a thorough recapitulation of elementary geometry (Output is equal to the area of either shaded triangles), and studies of Figure 1: Putmax = (U0 Un-(2ia0-iamin) Ri0) (ia0-iamin) = = (210-23 - (0.375 to 0.05) * 300) * (.186 to .05) = 12.2 W where Un = 23V (see fig 1) Ri0 = internal impedance according to previously. Consistent with theory, the estimated effect transferred to the speakers on their impedance Rn via the transformers can be converted into tubes anodimpedans - Raa = 1200ohm. For this omstättningskoefficienten Ktr be: for Rn = 4ohm: Ktr = Ra-a/Rn = 1200/4 = 17.3 And for Rn = 8ohm Ktr = 1200/8 = 12.2 Fortunately, it turns out that by combining the windings of the output transformer, the  we obtain turnovers near the ones we were looking for. We connect a load to 4ohms 8ohmsuttaget we have a turnover in 1300. Quite close to the ideal. And if we connect an 8ohms load to 4ohmsutaget where we connected in parallel windings, we obtain an equally perfect alignment. After these theoretical excesses, we can simply restart the modification of our amplifiers. The diagram shown is based on ideas from the 40-50 century, but meets practically all performances if the pipes superiority over the transistor. Short on schedule. The thick lines in the figure and the components should be connected as close together as possible, and the other completely behind schedule. cable between A and B, but also to output transformers shall be selected map high sound quality. The same also applies to C2, C3 and C4. Although the output transformer seems completely symmetrical it can be connected between the pipes anodes and speaker connections in several ways. With regard to the correct phase, different connections tested and test for the best sound. For the amplifier to get two separate 225V power supply, power adapter must be made of some. Thus: Parting 192v windings (links 1-4) and 115V windings (15-16). The windings of bias (50V), primary (220V) and filament (6.3 or 12.6V) should not be touched. We have now two windings with respective 96V or 57.5V. Each bobbin wound now at 30 turns of copper wire (I used 0.8mm - went to about 9m/bobin) giving additional 11.5V. Connect the three windings (96V, 57.5V, 11.5V) on each spool - with the right phase, to thus get two 165V voltages. These rectified and filtered, and then receives two 225V DC voltages. (One tip is to use the PSU board and the rectifier is there, cut copper tracks and drag new wiring. Bias voltage is not used at all, but keep an eye on voltages glow! Same method can be used to assemble each amplifier. clear the cards gently from components and use the existing wiring pattern as far as possible. Z. A.) When the amplifier is ready, do the following: connect a resistor of högtalaranlutningen, and set amplifier next to a turned-on television. If the light does not go off or the TV is disturbed out after you press the ON position, relax and verify  that tensions do not differ more than 5%. Measure the data if you like. So it looked like to me: Frequency Response, 4ohm 6Hz - 40kHz 8ohm 15H-45kHz Put at 10% THD 12W S / N 95dBA Sensitivity 400mV Input 500Kohm After completing his subjective measurements, we can now listen. But I'm wary of reviews, because I do not want to take the blame on me by readers, for having promised way to stroke-paradise. But I hope that first impressions still be that the base has become more energetic and better articulated, to human voices become more physical, natural and a significant broadening dynamics. The great work remains after the onset of the amplifier. The most difficult thing now was to achieve tonal balance, after carefully trimming and balancing of the components and cables. The output tubes and transformers still gives a certain coloring of the sound, especially in the midrange. But you'll still feel satisfied - amplifier consider all the benefits far its disadvantages. Finally, I hope that hemmapularen should not fear that modding is not too difficult. With good touch with a soldering iron and a bit of basic education - as Peter Kvartrup successfully demonstrated - all will succeed. © A.M. Likhnitsky and Audio Magazin SPb, Russia
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