I started with a ship full of max-level veterans, and I'm just a complete noob.

When Old Sun returned carrying the wrecked casing of the broken radar trigger, the paint on the metal casing had peeled off into dark gray scales, which fell off the door frame with a rustling sound.

He placed the item at the end of the worktable, then loosened four fixing screws and lifted off the top cover.

Most of the circuit boards inside had already been removed, but the black pulse transformer at the bottom was still quietly sitting in its original place.

The primary coil is wrapped with a complete enameled wire, and there is only one spot of corrosion the size of a fingernail on the iron core.

Old Sun pulled out a piece of fine sandpaper from his toolbox, dipped it in transformer oil, and quickly smoothed out the rust spots. He then ran his fingers over the surface of the iron core before nodding in approval.

"The core is usable, but the secondary winding needs to be rewound."

Da Liu came in almost right after Lao Sun, carrying two high-voltage mica capacitors and a choke coil that he had rummaged through the old equipment box next door, all wrapped in old newspapers.

Jiang Ming spread the sketch out in the center of the table, and placed the tip of his pencil next to the pulse transformer symbol.

"The primary winding remains unchanged at 12 turns, the secondary winding at 40 turns, the step-up ratio is 1:3.3, the dry cell battery input is 12 volts, and the secondary output is approximately 40 volts peak voltage."

"Forty volts is the upper limit."

Old Sun was already removing the retaining ring next to the primary coil, his voice muffled by his bent-over posture.

"You said that if it exceeds 40, the coating will be damaged, and the winding tolerance needs to be left with a margin."

"That's about 35 volts output after 35 rotations, and the field strength is in the middle of the safe range."

Old Sun straightened up, weighed the wrench handle in his palm, then rummaged through the bottom of the toolbox and pulled out a roll of fine enameled wire and a hand-cranked winding frame. He then glanced at Big Liu.

"Go measure the length of the thirty-five loops of line, and I'll wind it."

Xiao Zhao shouted from the testing stand: "262 hours exactly, number 04 is 283.2, which is 0.2 points lower than last time."

Jiang Ming responded, his eyes fixed on the location of the resistor-capacitor delay circuit on the sketch.

The pulse width is determined by the product of the resistance and capacitance, and it requires a width of about 4.7 microseconds.

The mica capacitor I have on hand has a nominal value of 1000 picofarads, which, when paired with a 4.7 kΩ resistor, provides a time constant of 4.7 microseconds.

4.7 kΩ is not a standard resistance value, but it can be made by connecting 4.3 kΩ and 390 Ω in series.

When Da Liu handed over the resistor box, Jiang Ming immediately gave two numbers.

Da Liu found the carbon film resistor with the corresponding color rings, checked its resistance value with a multimeter, cut off the leads, and handed it over.

At 1:40 a.m., Lao Sun fixed the wound pulse transformer onto a piece of plywood.

Next to it are arranged the oscillation circuit board, the thyristor trigger module, and the DC blocking capacitor.

All the connections between the components are single-core copper wires salvaged from scrap equipment.

The solder joints were made round and full by Lao Sun using rosin.

Jiang Ming squatted on the ground and used a multimeter to check the output waveform parameters one last time.

With the oscilloscope probe clipped to the secondary output, a clean negative spike appears on the screen, with an amplitude of 36 volts and a width of about 5 microseconds.

Xiao Zhao leaned over and took a look: "It's 0.3 microseconds wider than planned."

"Within the permissible range."

Jiang Ming stood up and looked at tube No. 4 of the test stand.

The vacuum tube casing reflects a dull metallic sheen under fluorescent light, and there is a spare terminal next to the anode pin.

That was the test port that Lao Sun reserved at Jiang Ming's request when he installed the pipe.

"The coupling line is connected from here."

Jiang Ming used tweezers to hold a thin wire with an insulating sleeve and soldered it onto a spare terminal.

The other end is connected to the secondary output of the pulse generator via a DC blocking capacitor.

Old Sun stood to the side, clutching a piece of dry cotton cloth in his hand, ready to disconnect the battery power supply jumper in case of an accident.

Xiao Zhao took two steps back, but his eyes never left the micro-annual dial.

The workshop was so quiet that only the hum of the lamp filaments and the faint vibration of the fluorescent lamp ballasts overhead could be heard.

"beat."

Jiang Ming pressed the start button on the pulse generator.

A very narrow reverse spike appeared on the oscilloscope screen, the microammeter pointer jittered down less than half a division, and then bounced back to its original position.

284 graduation mark.

No penetration.

Old Sun let out a long breath, loosened the cotton cloth in his hand, and then clenched it again.

"Set to trigger automatically every sixty seconds."

Jiang Ming turned the timer knob and heard the relay click to engage.

From this moment on, a microsecond-level reverse pulse, emitted once per minute, begins to be injected into the cathode coating of tube B04.

Like an invisible hand, it pushes back impurity ions that are trying to slide down to the interface every sixty seconds.

The first twenty-minute cycle has passed.

The microammeter needle remained firmly on 284, without the previous drop that occurred every twenty minutes.

Xiao Zhao's pencil hovered above the recording paper for a long time before finally writing down only one line: "262h40m, 284.0, no fluctuation."

The second cycle, 284.

The third cycle is still 284.

Old Sun finally threw the cotton cloth back into the toolbox, his voice carrying a heavy sigh that had been suppressed for a long time.

"What do you call this, repairing pipes while they're on?"

"It's not repair, it's preventative maintenance."

Jiang Ming's attention had already shifted to the No. 5 pipe next door.

Based on calculations, the exposure window for COVID-19 is between 280 and 300 hours. Currently, it has only reached 263 hours, leaving a window of more than ten hours.

"Old Sun, wind another set of coupling coils and connect it to number 05 as well. Clean it before it shows any symptoms."

"OK."

Old Sun turned to get the enameled wire. As he passed the pulse transformer, he flicked the edge of the iron core with his finger and muttered to himself, "I've put some oil on the rusted part of this iron core. It should last for about a hundred hours. After that, I'll have to replace it with a new one."

Jiang Ming nodded and noted down the time limit.

Da Liu has already started measuring the lines.

Xiao Zhao turned to a new page of the hourly record sheet, hesitated for a moment at the margin with his pencil tip, and wrote the words "electrosurgical procedure".

Then, he felt that this was not a formal term, so he lightly crossed it out with the side of his pencil, leaving only a light gray mark.

At 3:00 AM sharp, the welding of the second set of coupling circuits was completed.

A pulse injection line of the same specification was also connected to the spare terminal of tube 05.

The two pulse generators operate synchronously, and the timing relay clicks twice per minute, with a difference of half a second between each click.

Jiang Ming stood in front of the test stand, his gaze sweeping from 04 to 05, then to 01 and 02.

The microammeter pointers of both the 01 and 02 have been held in the same position for over 100 hours without any fluctuation.

The thicker coating provides a buffer margin, which plays a maximum protective role in these two pipes.

But his gaze lingered on the filament ammeter of tube number 02.

The dial of that small watch has extremely fine markings; the normal value is 0.85 amperes.

Jiang Ming remembers that the reading sixty hours ago was 0.85.

The hands are now at 0.87.

Over the past ten hours, the filament current has increased by 0.02 amperes.

This is not a problem with the coating.

The increase in filament resistance over time indicates that the tungsten filament slowly evaporates and thins at high temperatures, reducing its cross-sectional area and thus increasing its resistance.

Under constant voltage power supply, the current should decrease.

But now the current is rising again, there is only one possibility.

Localized overheating occurs in a certain part of the filament, causing an abnormal decrease in the resistivity of that section, resulting in a decrease in the overall equivalent resistance and a corresponding increase in current.

Localized overheating is a precursor to filament breakage.

Jiang Ming's pencil tip poked a small dent in the notebook and remained there without moving.

He can push back coating impurities, but he can't push back filament evaporation.