Liu Guoliang
Be
I bought a pair of "dawn" 5K 50W output cow, and there were more than 10 EL34, a large number of 6SN7 and 6SJ7 in the family, and in many lines, in many lines, I selected "Maland" 8b is the foundation, and after a number of modifications, finally decided to adopt the line of this paper. line
"Mal Shi" 8B is the zoom in the 6bh6 five tale, so its voice is beautiful and clear, and the marantz 9 is angry, and the world is very different. It can receive superlinear and triode output. There is a 35W output when it is connected, and the triode will also have 17. 5W power, so the problem of insufficient power is not serious except for some kind of speakers with low efficiency. The unit is connected to the third stage of 6SN7 by 6SJ 7, and 6SN7 is directly connected to the second stage, and then use 0. μF capacitance to the third stage EL34 as power amplification. The entire line is simple and straightforward, except for the bias, there is no place to adjust.
6SJ7 is a five-priced cutting, which can be regarded as the ancestor of EF86, and its characteristics and EF86 are also very similar. It has two varieties of iron shell and glass. Generally speaking, the tube of the iron shell tube is more sweet, while the glass tube will be relatively transparent. Take the RCA number 5693 Body tube is the most famous. If the iron shell tube is used, the first foot is required to pick up the shell, not grounding, otherwise, it will cause noise.
6SN7 is a very popular double tripode, which is also very similar to 6FQ7. Ou and Midea have produced production, including GEC B65 and RCA 5692 for its best. The ECC32 is different from the 6SN 7 due to the filament current and characteristics, so it cannot be used directly instead of 6fsn7. EL34 doesn't have to say more, it is a five-pole ventilation Mullard double circle, the old "German" and "blow horn" have the most enthusiastic friends, and their worth do not, the new paired NOS is also very difficult. beg.
Make
After half a year of time collection parts and modified lines, the most painful I sequence finally started. I put a 50-inch length, 2 inch x-half of the aluminum tank into a rack, and then mounted two 12-inch × 12-inch aluminum plates on the rack with screws, so that a cost is low and fast. finished.
1 parts such as power transformers, 1 choke, output transformer L, select 3, adjustable potentiometers and 8 eight-foot pedal seats, etc. are installed on only 12 inches × 12 inch aluminum plates. It is also very difficult to minimize each other, which is very difficult, and the part distribution causes noise, only the position of disassembly and reorganizing all parts can be completely solved.
Put a large pile of parts on the chassis, keep interchange the position, after several big night's efforts, finally find a reasonable layout.
It is necessary to use electric drills on the chassis, "let" comb, reamer and hand embarrassment, etc., the holes that do hundreds of large and small rounds are a very difficult job. After several weeks, all Kong Yi The picture is completed, but the hands have been scarred, and the installation and welding parts are much easier. It is only necessary to use all parts in the chassis in the chassis with a few days.
test
Carefully examine all parts, and sure everything is correct, then adjust the bias to the minimum position and connect the power supply. Half minutes after the boot is normal. When the measuring meter measuring work voltage is taken, there is a sound in the sudden space. Sparks splash, you have to close the power immediately. Experience, this phenomenon is mostly due to the incorrect output transformer primary phase is incorrect. Thus, the output of the passage-off capacitor output is interpreted to each other, and after the power is connected, everything has been replied to normal.
After testing and taking all the operating voltages, the working current of the EIJ34 is tested to 30 mA. When the start is very smooth, there is no difficulty, but when the third EL 34 is adjusted, the bias potentiometer is adjusted to half, and the multi-purpose meter does not respond, and then a little bit, the current is urgent Growing up L 80RNA, while the EL34 screen is extremely red. So immediately close the power to avoid the EL34 to be burned, and remove the bias potentiometer to check it. When it is less than half position, the resistance value is almost zero, but just greater than half position, the resistance value has reached 20k, hehe! Whether you can use it carefully, you should use it carefully. Because the burning is small, the burnt cattle is heavy. After replacing the abnormal VR, adjust the power of the EL34 to 30mA, and simmer it 3 nights, then transfer the current to 40mA.
Testing the voltage of all work points and definitely no DC output, connect the megaphone into the audio combination of the home. After the start of the time, adjust the predecessor volume potentiometer to 9 o'clock, the music sounds, but the dynamics are not good, it seems to have a slow half. So the feedback resistance is changed from 4.7k to 5.6k, and when the music sounds, the performance in the whole machine is very different, it becomes lively, high, medium and bass, and stunned, bright and clear. After increasing the resistance to 6. 2K, the volume becomes large, but it is a bit out of control, and the volume potentiometer has been significantly distortion at 8 o'clock.
Audacity
This machine is made of eight foot large tubes and "dawn" output transformers, and the original "Malang" 8B is not the same, so the sound quality and style have a lot difference.
The native tone is not "Malsh" 8B noble, but the music and the feeling of air are more rich. When the three-pole output is changed, the sound is smooth and meticulous, and the 300b single-ended machine I use now, the sweetness of the 6V6 push-pull machine, but the driving force is much stronger.
Summarize
In addition to using EL34, this machine can use KT66 and 6GB8 and so on, as long as the negative bias is properly adjusted. Due to the B + voltage up to 435V, in addition to the manufacturer's special statement of the 6L6 series of strong discharge pipes can be used for high voltages, it is not necessary.
This machine is refined, not unaffordinated, welding is easy, as long as the positive and negative and feedback resistors are required to make appropriate adjustments to different output transformers, the required parts are easily found. "If you are interested in manufacturing a moderate, you can trial, you can trial, and the chance of success is very high.
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