FU-50 push-pull, Fu-50 Power Amplifier
Keywords: FU-50 push-pull
FU-50 push-pull
The FU-50 is a strong sense of superb atrophotic oxide pole shot five-pole, the appearance and internal structure, the main purpose of this tube is high frequency oscillation and power amplification, the author with a strong curiosity Explore the mystery applied to the audio.
First, a pair of push-pull output transformers are produced, in order to facilitate adjustment impedance, the output transformer prepares the tap of multi-group transform impedance. In order to ensure that the two arm inductance and DC resistance are basically consistent, it is not taken in the primary winding, and the primary winding disposable layers are completed, the four-layer structure, the outer layer is one arm, the middle two layers are another One arm, in order to ensure that the primary has a large amount of inductance, the number of turns of the windings is more than 3,000 turns, provided that the core window can accommodate. Through the impedance than the secondary winding grade, the screen is 8kΩ, 7kΩ, 6kΩ, 5kΩ: 8Ω, 4Ω tap.
The application data of the tube is: screen pressure 800V, curtain gate pressure 250V, gate negative pressure - 55V ~ -25V, maximum cathode current 230mA. According to the hand on the hand, choose a more antique conservative old circuit. The power transformer is a self-made vintage electronic tube black and white TV power transformer. The primary winding has a tap of 240V, 220V, 200V, 180V ~ 0V. The secondary high voltage winding is 285V, 265V-0V, and a filament transformer is provided with 12.6V, 6.3V. Voltage, in order to reduce the thermal noise between the filament and the cathode, add a DC voltage of less than 100 V on the filament, filter 4 220μ / F500V electrolytic capacitance, parallel 4μF, 2μF / 500V oil immersion capacitance, and the like to reduce capacitor Array, the minimum capacity is 2200 pF / 500V. The main circuit is completely recovered quickly of 800V / 6A rectifier bridge, and high and low voltage two switch controls to extend the service life of the pipe.
From the perspective of the circuit, 6N9P is a total of, 6N8P promotion is very common, and the coupling capacitance and cathode bypass capacitors at all levels have chosen CBB capacitors, porcelain-sealing paper dielectric capacitors and oil immersive capacitors. Third, four The alignment of the capacitance is combined before and after, and the changes in sound are listened. The inverted phase level uses a partial voltage automatic balance inverting circuit to reduce the cumbersome of the debugging. It is only necessary to change a few tubes and screen resistors when debugging. It can be basically commissioned. To be strictly grounded, check that the air machine is turned on to check the voltage. After basics, insert the tube, then measure the respective points, the high-voltage transformer is in the 220V position, the Fu-50 tube screen should be around 350V. The curtain is passed around 345V. Output transformer screen to the screen impedance is 6kΩ, and is connected to a super linear connection, the curtain gate is string 3 kΩ resistor, the curtain stream is about 3mA, the cathode voltage is 34V, the single tube two screen flows about 80mA, and the two arm two tube cathodes Voltage commissioning is the same size, no signal input, the speaker has almost noise. Be
Feed the signal amplified, the machine is smooth, plus a little volume, the sound is characterized, and the performance of the FU-50 tube is indeed not general. By repeated comparison with the 6P3P push machine of the same circuit, it is worth high frequency tube. High frequency band is much bit more than 6p3p. Then further increase the power attempt to change the tap of the high voltage transformer to 200V and 180V (should pay attention to the voltage of the electrolytic capacitance), when the screen rises to 420V, the gate negative pressure -40V sound and details are more beautiful Some, ideas to raise the screen to about 600V, and the Fu-50 should have a better performance. The Fu-50 tube should be a very good tube from the cost performance ratio.
I don't like to describe the effect of the music, I only admire the ear, but here is the characteristics of Fu-50 tubes, I have to use the language of the enthusiasts to describe a few words. In general, the audio manifestation of the tube is particularly excellent in high frequency sections, very clear, bright, medium frequency bands, and round. Appreciate "Missing" is very rich in the violin, sweet, full of hall. The rhythm and gunshots in "Hunting Bolka" are very shocking, "Alaska" three-song troops in the fourth song of "Alaska", especially the last sound can be said around the three days. The drum of the rage gold disc "Knife will be prelude", the drum fuse is close at hand.
The above is the initial feeling of the experiment of the tube, and the enthusiasm of the FU-50 tube is exchanged with each other.
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