1969 Xiaojia amplifier

Try to use the ones recommended by the original work: For Q1 and Q2, choose 2N3055. For Q3, the original work is 2N1711/2N1613/2N697. If not, choose the very easy-to-find 2N5551, which is fully capable! Q4 The original one is 2N3906. If you don’t have it, use the very easy-to-find 2N5401, which will do the job! 2N5401 and 2N5551 are pairs of tubes, and many domestic audio circuits use them. If you have a pair of TIP41 and TIP42 tubes, that’s fine too, and the sound quality is pretty good! These 2 tubes are also easy to find. Found: Q3 The sound quality using TIP41C is better than the bass effect of 2N5551! ! ! Replacing Q4 with a different type of tube will not have a significant impact on the sound quality, but replacing Q3 with a different one will have a significant impact on the sound quality, especially the bass. The sound quality is better when using TIP41C than 2N5551. If you don’t believe me, try it yourself. Q4 If the installation polarity is wrong or the tube is used improperly, the midpoint voltage cannot be adjusted to half of the power supply voltage by adjusting RV1! If it is correct, speak as usual. But if the adjustment is less than half of the power supply voltage, do you know what the consequences will be? It's just that the two 3055 tubes heat up differently, which is why some people say that one of the two tubes in their power amplifier is hot and the other is not. I used the domestic gold-sealed tube 3CK8D, and the sound was normal, but the midpoint voltage was adjusted to less than half of the power supply voltage, and the deviation was very severe! If the polarity of Q4 is wrong, or the tube is broken, there will be a phenomenon that the 3055 tube has no current, and the midpoint voltage is the power supply voltage. As long as Q4 is selected correctly, the component parameters in the original work and the midpoint voltage after installation and testing generally meet the requirements without adjustment. If your midpoint voltage is never adjusted to half of the power supply voltage, replace it with Q4! Q3 uses different tubes, and the quiescent current is different, even very different! After changing the tube, you need to adjust the current! Therefore: Q4 affects the adjustment of the midpoint voltage! Q3 affects the adjustment of quiescent current! If Q4 is broken or the polarity is wrong, the voltage and current will be abnormal! If C1 and C4 are from different brands, the sound quality will be different! C4 is not recommended to be too large! 2200UF Finally the original is enough! If you switch to 3300 or 4700, the sound quality may deteriorate.