A light hearted look at where valves come from

By Mark Brighton

In this little article, by way of introduction, I am going to talk a little about valves, and why they were so important in forming the society and way of life we enjoy today.

Once upon a time, many years ago, we all sat at home and had nothing to do. OK, there were books, and if you were rich maybe you had a piano in the parlour that you could gather around and sing at, but I can imagine that the long dark evenings could get rather boring sometimes, and many people went to bed early.

If you did stay up, it was hard to read anyway by candlelight, paraffin lamps or (for the better off again) the sputtering light of gas lamps.

So, when Thomas Edison redeveloped the light bulb to make it practical to manufacture and to use in the home, things started to improve for those that could afford electricity, but he very soon found something he didn't expect. Whilst experimenting with different ways of making light bulbs (he was apparently trying to reduce the problem of soot forming inside his bulbs) he noticed that if he made bulbs with an extra plate of metal inside the bulb near to the glowing filament of wire, that a current flowed from the filament to the extra plate.

At this point I am going to take a step back to some very basic physics of electricity, nothing heavy, but if you want to skip this bit, then I will sigh sadly and try to understand....

Electricity is essentially the flow of electrons from one place to another. Electrons are very very tiny whizzy charged particles that form part of the atoms that everything, including you and me, are made up of. As far as electronics is concerned there are two types of things.... those that conduct electricity (conductors), and those that don't (insulators). This is a bit black and white, because there are loads of things that do conduct a bit (again, like you and me), but aren't very good at it, but we need not complicate things even more!

So.... atoms have a nucleus, or centre, which has a positive charge, and a load of electrons whizzing around them, which have a negative charge, and the whole thing balances out rather nicely. It turns out that there are loads of different configurations of the way an atom can be made up (and each different combination makes a different substance, like gold or copper or calcium or helium gas (there are of course many many more, but I am not here to type out the table of elements)).

Bringing it down to a simple analogy, atoms that have the right number of electrons for all their bits to be happily holding both hands are very strong, hard to break up, and are very good insulators... the electrons are fulfilled and joyous and don't want to leave.

However, atoms that are not so community spirited, have a lot of poor electrons being flung around very fast whilst only holding on with one hand, and they are much more likely to be flung right off or leave if they see a more attractive prospect elsewhere. Metals are very good examples of this sort of this unhappy arrangement, which is why they make very good conductors indeed.

All the "loose" electrons in these atoms need to leave the atom altogether is a nice strong positive charge nearby.... because a positive charge is a sure sign of a lack of electrons and so they know they will be wanted to balance things up with their negative charge, because balance is the way of the world.

So, finally coming back to Edisons experimental light bulb, the atoms in the carbon or metal filament were being heated incredibly by the force of the electric current passed through it until the extra energy made them glow almost white hot..... and those loose electrons were being REALLY shaken about..... flying away and falling back, hanging on to each atom in turn as they were flung along the wire and flew out of the filament into the copper wires connecting the bulb to the electrical power supply.

So.... when another piece of metal was introduced into the bulb, some of the flying electrons had enough energy to fly out and hit it and stick because it was more positive than home, which made it possible to measure this charge and indeed draw a current from it (which removed the extra electrons and freed spaces for more to come to). It's maybe worth reminding you at this point, if you ever knew, that an electric current doesn't (as would seem sensible) flow from positive to negative, but the actual flow of electrons is from a negative source (where they are all stacked up) to a positively charged place (where they are needed and attracted to). So, a current could flow from the filament, to the plate, but importantly, NOT the other way (no way home!).

So, when Thomas Edison did this, he created the very first Thermionic Diode, so called because its activated by heating one electrode, and itís got a total of two electrodes (ok the filament has two, but they are effectively joined together). This was useful for various things we won't go into here, because itís not part of what I am rambling on about.

Some years later, various clever people experimenting with these diodes discovered the really Earth changing fact that if you put a grid or mesh of metal in-between the heated negative terminal (the cathode) and the positive plate (the anode) and put a small negative charge on it, the electrons flying out from the cathode found it harder to see the attraction of the anode and came across in smaller numbers. If you increased this small negative grid voltage further (more negative), the diode (which was now a triode... three terminals) would shut down and no electrons would jump from cathode to anode.

So, from no charge on the grid (diode on, current flows) to a certain negative charge on the grid (diode off, current stops), you suddenly have an electronic switch, controlled by a small voltage on the grid. Now this was also very useful as a switch, but it STILL isn't the most important thing about a triode.

The most important thing about a triode is what happens in that area between being fully on, and fully off. In this area, the current flowing through the triode valve (you see.... a valve in plumbing is a water switch, turns flow on and off?) varies and is controlled by a much tinier voltage/current flowing into the grid connection. And a tiny varying voltage or current controlling and producing a big varying voltage or current is called AMPLIFICATION!

Amplification is a very very important thing indeed. It made a lot of things possible that were not possible before. Before I go on to explain that, letís go back to Bernard sitting in his parlour reading Dickens by lamp light in total silence.

Bernard did have some access to Electrical Wonders and Inventions already. For many years, he could have gone to his Post Office and sent a telegram to his Auntie Edna living in the colonies far across the seas. We already had electricity, and all the telegraph did was to switch it on and off via a key switch in Morse code, prestoÖ early text message sent.

Thanks to the work of Alexander Graham Bell and others, and the invention of the carbon microphone, it was also possible to send speech converted into an electrical current along the telegraph wires, to be listened to with a small carbon earphone at the other end using the new fangled Telephones, although without amplification their range was limited.

Both of these technologies are limited by something called "resistance". As the name implies, resistance in a wire or other conductor is what stops every electron in the chain all along the conductor from causing one to appear at the far end. Some of them stop and find new atomic homes, adding energy to the atom concerned, which vibrates and creates a little heat, converting the energy the formerly free whizzing electron had built up in its dash, and reducing the electron flow or current. Now imagine a large number of these little events happening and you will see that you won't get as many electrons out at the far end of the wire, due to this "resistance". Indeed, if it wasn't for resistance, the light bulb wouldn't be possible.... no heat would be generated and it would never glow!

What had been needed to overcome this problem, was a way to "boost" the reduced current at the far end of the wire back up again...... or AMPLIFICATION! Enter the Triode!

Not only did this greatly extend the usefulness of the telephone, it also opened up other new and exciting possibilities in other areas that would change the way we live our lives.

Heinrich Hertz (as in Megahertz) and Marconi had pioneered development and understanding of the science of Radio Waves, but without any amplifying devices, the transmitters and receivers of the time were very simple and could only send and receive Morse code, like a telegraph, but without wires.

The invention of the Triode made it possible from 1920 to build a circuit called an oscillator, which relies on amplification and feedback to work, and the triodes in these transmitters were used both to oscillate.... which if done fast enough can be fed into a wire and radiate electrically through the air (transmit).... and to modulate, which is where an audio signal from (say) a microphone is amplified up to a level that can be used to vary the output of the oscillator, embedding the audio signal into the transmission and.... for the first time.... making it possible to send out speech and music through the air.... wirelessly!

And so was born the era of the BBC just two years later in 1922, sending out radio transmissions across the Empire and to all the World. Initially, the high cost of the valves meant that the transmitting studios had them and Bernard and his fellow friends at the Dog & Bull could only use a very simple radio called a Crystal Set which was very very very quiet (with no amplification, it had only the tiny bit of energy recovered from the radio signal into the long wire aerial) and could only work with headphones in a very quiet room, with the kids and wife locked at the other end of the house with instructions to remain extremely quiet.

Luckily (for Bernards marriage), within a few years, lots more valves were invented and mass produced, Wireless receiver sets were built and sold to the middle classes, and the pianos gathered dust and slowly went out of tune as the family gathered around the warm friendly glow of the Wireless Set instead in the evenings to listen to Jolly Family Entertainment and News Broadcasts from London and around the Empire on the BBC.

Bernard stopped inviting the Browns from next door around to sing at the piano with him, as he preferred to listen to the Wireless, and so began the fragmentation of community life as it had always been, a process which has continued to the modern day, where we see the latest events unfold live before our very eyes on the BBC news, or on CNN from half way across the world.... as they actually happen.... and yet we often don't even know whatís happening next door but one. Maybe that bit isn't entirely A Good Thing, but then itís not the technology, itís what we choose to do with it!

Valves made it possible for the telephone, the radio, the television, hi fi amplifiers and radiograms that replaced those tinny wind up phonographs and eventually the first real computers to be invented. They were eventually superseded by the tiny Transistor, which then went on to spawn the mighty Silicon Chip or Integrated Circuit, but between 1920 and 1960, the valve reigned supreme, and was still used in TV's through the introduction of colour and until the early to mid 1970's, and a few specialised valves survived even longer than that, like the Cathode Ray Tubes that were the TV screens we all watched (and some still do) until LCD and plasma TVs came along, and Microwave ovens, where your food is cooked by..... yes, you guessed it, a valve.