真空三极管：发明历史和物理工作原理

Posted 2023-01-23 卓晴

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真空三极管是：发明历史与工作原理

01 Triode Valve

Before the invention of the transistor, the most important piece of electronic equipment was the vacuum triode. All radios used them, early television used them. Heck, even early computers had rooms full of these jacked-up light bulbs, but how do they work and how and why were they invented? This is a story of a smudge on a light bulb, an assistant with a good memory, and a con man working around a pack. Ready? Let’s go!

It all started in 1880 with the regular light bulb. Thomas Edison had noticed that, when his light bulb broke, they would often create black smudges on the inside of the bulb, near the positive end of the filament. He had worked very hard to make good vacuums so, he was pretty sure that they were not created by any substance inside the bulb. Therefore, he deduced that they must be something coming off of the filament itself.

He then added a plate to the bulb with a hope that whatever was emanating from the filament, would stick on the plate, and possibly keep the filament from breaking in the first place. The plate turned out to be not much help. However, he noticed that if he added another battery between the filament and the plate, something strange happened. The current could flow if the plate was positive, but would not flow if the plate was negative. Edison patented as a volt meter, although he didn’t really know what was going on, or why anyone would want this expensive and ineffective volt meter.

What was going on? Well, it all has to do with the movement of negatively charged electrons. In the light bulb. When the filament got hot, the electrons could become free. When the filament broke, the electrons would fly towards the positive end and leave that black smudge. If before the filament broke, you added an extra voltage between the filament and the plate and the filament was negatively charged and the plate positive, the negatively charged electrons could easily jump off the filament and onto the positively charged plate, and let the current flow. If, however, the plate was negatively charged, then the electrons would stay on the plate as it was cold, and not concentrated on the thin filament. This was called the Edison effect.

Although aside from patenting it, Edison wasn’t much interested in it. However, Edison had a young English technical advisor named John Ambrose Fleming who was interested. Fleming was there to help Edison with alternating current, which Edison quickly decided to reject and sent Fleming back to England. Jump forward 24 years to October of 1904. By this time, Fleming had become a technical advisor to Guglielmo Marconi, helping him with sending wireless telegraph signals. Marconi’s biggest problem in 1904 was in his receiver. Marconi used a tube with little filaments that would stick together or cohere when a radio wave went through it and then would be tapped when the signal was complete. It was slow, and awkward and inefficient.

According to an engineer at the time, the coherer “was publicized as wonderful, and it was wonderfully erratic and bad. It would not work when it should, and it worked over time when it should not.” The year before in 1903, a Canadian named Reginald Fessenden, had made an electrolytic detector, that used a chemical reaction to rectify or filter out one direction of the current, So that it could be heard on headphones. Fleming felt, that the detector did not work well at high frequencies. Also, they didn’t hold the patent.

He was thinking about the problem when he had, according to him, a sudden, very happy thought. Why not try the lamps? He wrote to Marconi, “I found a method of rectifying electrical oscillations” that is, making the flow of electricity all in the same direction.

By November, Fleming filed for a patent for what was called a Fleming valve, or a vacuum diode, di for two, ode for path. Note that the Fleming valve, was exactly the same as the Edison effect valve. What was different was how he used it. So, let’s talk a little bit about what Fleming did. Fleming used an antenna with a coil to receive the radio signal. He then had another coil so that the alternating current in the first coil, would induce an alternating current in the second coil. He then had that signal go through a sensitive current meter, called a mirror galvanometer, and had one end of the signal go to the plate, and one to the filament of his valve, heated by a battery. The valve thus made the signal one way, so that the meter turned in one direction and could be recorded.

Fleming did not use headphones, possibly because he was partially deaf. This worked pretty well, but it was not very popular as it was expensive, and most people started using semiconductors, and what were called crystal sets as rectifiers instead. However, one person was very interested in the Fleming valve and his name was Lee de Forest. At the time, Lee de Forest was being sued by Reginald Fessenden for copying his electrolytic detector. So, de Forest was on the hunt for a new detector.

We know de forest had read about the Fleming valve, because in December of 1905, De Forest filed for a patent. They used what he describes as “an electric valve, which has been fully described by J.A Fleming”. then five weeks later, deforest files for a patent for a new detector, that is strikingly similar to the Fleming valve. They both had a filament and a plate in the vacuum tube, and he did the filament with a battery. They also both took a radio wave from an antenna and passed it through the valve between the plate and the filament.

In fact, there are only four very minor differences. First, de forest used headphones instead of a current meter. Second, he added an extra battery that didn’t seem to do much. Third, He didn’t use parallel coils, at least in this circuit. And forth, he incorrectly thought the trace amounts of gas in the bulb were ion nodes, and that was what was causing the current to flow. So, he insisted that the bulb not be a perfect vacuum. Because this device was used to make sound, and he incorrectly thought it had to do with the ionization, of gas. He dubbed this an audion.

Not surprisingly, Fleming sued. Meanwhile, de Forest started adding pieces of metal all over the place. He wrapped his valve in tinfoil. He circled the outside of it with wire. He had multiple connected plates inside the bulb. Then on Christmas day of 1906, de Forest ordered the bulb with three connections, the filament, the plate, and between them, a wire that was bent into a zigzag shape that he called a grid. Adding the third wire in the middle was described in 1922. As “the most important single step taken in the whole development of radio communication.”

So, what did the wire do? Well, imagine you set up a vacuum triode by heating the filament with a battery, and attaching a separate voltage so that the filament is negative and the plate is positive. In this case, the electrons would jump off the heated filament, past the grid wire, and onto the plate.

Now, imagine, adding a weak signal to the grid wire. If you add a signal where the grid wire has a positive charge on it, many more electrons would be attracted to the grid, and jump off the filament, and onto the plate. This would vastly increase the current on the plate. If you add a signal to the grid wire with a negative charge, however, it would block the negative electrons from jumping onto the plate drastically reducing the current.

In this way, small changes in the grid wire can make big changes in the current coming out of the plate. This was both an electric amplifier, and an electric rectifier, or one-way valve.

Unfortunately, Lee de Forest, couldn’t get his device to work that well, and he mostly just used it as a complicated rectifier. In addition de Forest was convinced, that you needed a little bit of gas to make them work. Possibly to distinguish it from the Fleming valve, which led to some low quality triodes, because the audion was expensive, and complicated, and had variable quality, very few people used it.

It wasn’t until five years after its invention, When a tenacious, undergraduate named Howard Armstrong figured out how to make the triodes sink, by feeding the signal back to it in a system he called regeneration. This is what made the vacuum triode, the Swiss army knife for the next 50 years. Meaning they used it for everything. -

Teah. If it weren’t for these babies, there wouldn’t be any radio. Yes, and a million others owe their jobs to the vacuum tube, including myself. As a matter of fact, practically everybody has been benefited by it in some way.

02 真空三极管

一、背景介绍

在晶体管发明之前，最重要的电子设备是真空三极管。所有的收音机都使用它们，早期的电视也使用它们。你知道吗，即使是早期的计算机也使用这些带有插座的真空管灯泡，体积巨大，充满了整间房屋。但它们是如何工作的？它们是如何以及为什么发明的？这是一个关于灯泡内部的污迹，一个记忆力很好的助手，和一个发明专利欺骗行为。这里面的故事让我们听 Kathy 老师娓娓道来吧。

▲ 图2.1.1 真空管计算机

二、灯泡里面的污渍

这一切都始于 1880 年的普通灯泡。托马斯·爱迪生 (Thomas Edison) 注意到，当他的灯泡坏了时，灯泡内部通常会在灯丝正极附近产生黑色污迹。他尽最大努力制造出优质的真空灯泡，因此他非常确定这些污渍不是由灯泡内的任何物质产生的。因此，他推断一定是灯丝本身蒸发出的东西。

▲ 图2.2.1 灯泡内部的污渍

然后他在灯泡上加了一个金属板，希望灯丝发出的任何东西都能粘在金属板上，并能在第一时间防止灯丝断裂。事实证明，这个金属板并没有多大帮助。然而，他注意到，如果在灯丝和极板之间添加另一个电池，就会发生一些奇怪的事情。如果金属板为正，则电流可以流动，但如果板为负，则电流不会流动。爱迪生申请了电压表的专利，尽管他真的不知道发生了什么，也不知道为什么将来会有人想要这种昂贵且无效的电压表。

▲ 图32.2.2 灯泡内部的金属电极板

这中间到底发生了什么事？好吧，这一切都与带负电的电子的运动有关。在灯泡里，当灯丝变热时，电子可以变得自由。当灯丝断裂时，电子会飞向正极，并带动灯丝物质在旁边玻璃壁上留下黑色污迹。如果在灯丝断裂之前，在灯丝和板之间加了一个额外的电压，灯丝带负电，板带正电，带负电的电子很容易从灯丝跳到带正电的板上，让电流流动。然而，如果板带负电，那么电子会留在板上，因为它是冷的，而不是集中在细丝上。这被称为爱迪生效应。

▲ 图32.2.3 灯泡中的电流

三、无线检波器

尽管除了申请专利外，爱迪生对此并不感兴趣。然而，爱迪生有一位年轻的英国技术顾问，名叫约翰·安布罗斯·弗莱明，他对此很感兴趣。弗莱明原本在爱迪生那里从事交流电技术研发，爱迪生看他不务正业，很快决定辞退弗莱明并将他送回英国。

▲ 图32.2.4 John Ambrose Fleming

岁月如梭，过了 24 年，到 1904 年 10 月。此时，弗莱明已成为古列尔莫·马可尼 (Guglielmo Marconi) 的技术顾问，帮助他发送无线电报信号。马可尼当时最大的问题是他的接收器。马可尼使用了一个内部带有细碎金属粉末管子，被称为相关检波器。平时它不导电。当无线电波通过它时，这些金属粉末会粘在一起或凝聚在一起，电极之间电阻下降，在电压作用下形成接收信号输出。然后在信号接收之后它被旁边电磁铁敲击恢复不导通状态。它很慢，笨拙且效率低下。

▲ 图32.3.2 马可尼的无线接收机

根据当时的一位工程师的说法，相干检波器 “虽然被宣传为很棒，但它相当不靠谱，而且糟糕。它在该导通的时候不导通，而在不该工作的时候却随着时间的推移导通。”

在此一年前， 1903 年，加拿大人雷金纳德·费森登 (Reginald Fessenden) 制作了一种化学电解检测器，利用化学反应对电流的一个方向进行整流或者去除，以便在耳机上可以听到高频无线信号。 Fleming 认为，检测器在高频下效果不佳。此外，他们没有持有专利。

▲ 图32.3.3 Reginal Fessenden 和他的电机整流器

四、真空二极管

据弗莱明后来回忆，当他突然想到这个问题时，非常高兴。为什么不试试灯泡呢？他写信给马可尼说，“我找到了一种对电子信号整流方法”，就是让电流都朝同一个方向流动。到 11 月，弗莱明为所谓的弗莱明真空管或真空二极管申请了专利， di 代表两个， ode 代表路径。

▲ 图32.3.4 弗莱明真空二极管

请注意，弗莱明真空管与爱迪生效应真空管完全相同。不同的是在如何使用它的方式上。那么，让我们谈谈弗莱明的所作所为。弗莱明使用带有线圈的天线来接收无线电信号。然后他利用另一个线圈与第一个线圈形成互感，这样第一个线圈中的交流电就会在第二个线圈中感应出交流电。然后他让这个信号通过一个灵敏的电流计，称为镜面反射检流计，信号的一端到达真空二极管的正极，另一端到达他的真空管灯丝，灯丝由电池加热。因此，真空管使信号单向流动，从而使仪表朝一个方向转动并可以记录下来。

▲ 图32.3.5 弗莱明的真空二极管检波器
弗莱明没有戴耳机，可能是因为他部分失聪。这种方法效果很好，但由于价格过于昂贵，因此不太受欢迎。而且大多数人开始使用半导体，并使用所谓的 晶体组合作为整流器。然而，有一个人对 Fleming 真空管非常感兴趣，他的名字叫 Lee de Forest。当时，雷金纳德·费森登 (Reginald Fessenden) 起诉 Lee de Forest 抄袭他的电解检测器。因此，de Forest 正在寻找一种新的探测器。

五、真空三极管

我们知道德福雷斯特了解过弗莱明真空二极管，因为在 1905 年 12 月，德福雷斯特申请了专利时，写到：专利使用了 “J.A 弗莱明 (J.A Fleming) 的电子管，弗莱明的专利中对其进行了全面描述”。五周后，Deforest 申请了一种新检测器的专利，该检测器与弗莱明真空二极管惊人地相似。在真空管中都有一根灯丝和一块金属板，他用电池驱动灯丝。他们还从天线接收无线电波并将其通过真空二极管中的阳极和灯丝。

▲ 图A32.5.1 德福雷斯特无线检波器

事实上，只有四个非常小的差异。首先，de forest 使用耳机代替电流表。其次，他加了一个似乎没什么用的额外电池。第三，他没有使用并联线圈，至少在这个电路中是这样。第四，他错误地认为灯泡中的微量气体能够电离而带电，这就是导致电流流动的原因。所以，他坚持认为灯泡不是完美的真空。因为这个装置是用来发出声音的，他错误地认为它与气体的电离有关。他将此称为三极管。

▲ 图32.5.1 德福雷斯特无线检波器与弗莱明无线检波器

不出意外，弗莱明对 de Forest 专利侵权提起诉讼。为了躲避专利诉讼，de Forest 开始在真空管设施中到处添加金属电极。他用锡纸包裹了他的真空管、他用铁丝在外面绕了一圈、他在灯泡内有多个连接板，不论是有用的还是无用的，他就乱加一气。在 1906 年的圣诞节那天，de Forest 将这些乱七八糟的真空管整理成有三个电极的灯泡，即灯丝、阳极金属板，以及在它们之间弯曲成之字形的金属丝，他称之为栅极。在1922年真空管中间添加第三根栅极，这个发明非同寻常，被描述为“人类在整个无线电通信发展过程中迈出的最重要的一步”。

▲ 图32.5.3 弗莱明的真空三极管

六、工作原理

那么，栅极做了什么？好吧，想象一下你通过用电池加热灯丝。附加一个单独的电压，使灯丝为负极，金属板为正极，形成接受电子的阳极。在这种情况下，电子会从加热的灯丝上发射，经过栅极线，到达阳极上。

▲ 图32.6.1 栅极可以控制电流

然后想象一下，向网格线施加微弱的电信号。如果在栅极上增加正电压，更多的电子会被吸引前往栅极，大部分穿过栅极达到阳极。这将大大增加阳极上的电流。但是，如果栅极线施加负电压，它会阻止负电子通过，从而大大降低电流。

这样，栅极上的微小电压变化就能使从阳极流出的电流发生巨大变化。这既是电放大器，又是电整流器，或单向真空管。

不幸的是，Lee de Forest 无法让他的设备工作得那么好，他大多只是将它用作复杂的整流器。此外，de Forest 确信，真空管内需要有一点气体才能使它工作。可能是为了躲避弗莱明真空管专利限制，这些夹杂着错误认识的做法导致一些三极管质量低下。因为三极管价格昂贵，结构复杂，质量参差不齐，所以很少有人使用。