Why do we need vacuum tubes, transistors..why not just use DC?

[Elite Engineer]

warning..this post is going to have some serious ignorance attached to it

 

so I get that the chronology is vacuum tubes > transistors > IC's....

 

I remember seeing an illustration of a vacuum tube. It had a battery/ power supply connected to the VT. The VT conducted electricity and then sent signals throughout the

 

computer. Why even have the power source (wall outlet basically) connected to the VT, and just hook up the power source up to the computer directly, with little

 

logic gates to get it work send 1's and 0's?

 

~ee

Edited June 20, 2017 by Elite Engineer

[EdEarl]

I don't understand your question, so whatever I say may miss the point.

 

Vacuum tubes aren't used much anymore in electronics, because they are slow, expensive, and inefficient. AC wall power goes through a power supply to generate one or more DC voltages to operate electronic equipment.

[fiveworlds]

Why even have the power source (wall outlet basically) connected to the VT, and just hook up the power source up to the computer directly, with little logic gates to get it work send 1's and 0's

 

 

Vacuum tubes used high voltages which would fry the logic gates if the power source was hooked up to the computer directly. Vacuum tubes of the time were also rectifiers in that they could convert an alternating current radio signal into direct current which could then be used to record music onto tapes/records.

[Janus]

warning..this post is going to have some serious ignorance attached to it

 

so I get that the chronology is vacuum tubes > transistors > IC's....

 

I remember seeing an illustration of a vacuum tube. It had a battery/ power supply connected to the VT. The VT conducted electricity and then sent signals throughout the

 

computer. Why even have the power source (wall outlet basically) connected to the VT, and just hook up the power source up to the computer directly, with little

 

logic gates to get it work send 1's and 0's?

 

~ee

Are you asking why a vacuum tube needs an external power source? If so, it is because in order to work, the cathode ( the part that emits electrons) has to be hot. Thus they include a heater that only job is to keep it hot. The circuit supplying power to the heater was separate from the signal the tube was acting on. This is why older radios and TVs used to have to warm up before they would start working. (one scheme used to get around this was to have the heater circuits of the tubes "on" all the time even when the device was off, thus the tubes were ready to go the moment you turned it on.)

[John Cuthber]

"I remember seeing an illustration of a vacuum tube. It had a battery/ power supply connected to the VT. The VT conducted electricity and then sent signals throughout the

computer."
I think your memory may be letting you down.

The only VT I ever saw in a computer was the CRT screen.

[Strange]

The question is very confused / confusing.

 

Both vacuum tube / valve and transistor circuits can be (and are) driven directly from a DC source such as a battery.

 

Valves requires at least two voltages a low one to drive the heaters (as mentioned) and a higher voltage for the actual signals being amplified (or whatever). The heater voltage was typically around 6 or 12 V and could be AC or DC. So if the system is powered from the mains(*) then the heaters could be powered by a simple step down transformer. A transformer, rectifier and filter would be needed to generate the right high-tension supply for the electronics. Or, all of them could be supplied from a battery.

 

Transistor circuits can run from a single supply voltage. For old TTL integrated circuits this was normally 5V (and had to be DC). With the adoption of CMOS gates, this was reduced to 3.3 or 2.5V to allow higher speed (and reduce power consumption). Modern ICs, such as microprocessors, use a number of different voltages internally. For example, 3.3V at the interfaces for compatibility with other devices but much lower voltages internally to allow for smaller devices and therefore higher speed operation.

 

 

(*) Is "mains" a UK-only term for the power from the wall outlet? Is there a US equivalent?

[Endy0816]

They can themselves serve as components of logic gates.

 

http://www.quadibloc.com/comp/cp01.htm

 

 

(*) Is "mains" a UK-only term for the power from the wall outlet? Is there a US equivalent?

 

In the US, mains electric power is referred to by several names including "household power", "household electricity", "house current", "powerline", "domestic power", "wall power", "line power", "AC power", "city power", "street power", and "electrical grid".

In the UK, mains electric power is generally referred to as "the mains".

https://en.wikipedia.org/wiki/Mains_electricity#Terminology

 

I wish there was "a" US equivalent

[Strange]

They can themselves serve as components of logic gates.

 

Indeed. So I'm not sure about John's comment. There were valve-based computers and so it is possible that Elite Engineer has read something about them.

 

 

 

 

https://en.wikipedia.org/wiki/Mains_electricity#Terminology

 

I wish there was "a" US equivalent

 

Thanks for that.

[Carrock]

I always liked thermionic valves, not least because you could actually see inside them and sometimes diagnose a dodgy valve by visual inspection.
So a defence....

Vacuum tubes aren't used much anymore in electronics, because they are slow, expensive, and inefficient.

Inefficient, certainly. AFAIK, magnetrons are still used in domestic microwave ovens.
Producing a few hundred watts at 2.45 GHz from a solid state device is still not cheap and it's hard to protect a solid state device from all the possible loads in a cooker.
Producing high power at high frequency, and the CRT, were the last holdouts against solid state devices.

However valves are much slower to die when you maltreat them.
I used to have an ancient A.M. transmitter with an ex battleship power supply that required four people to carry it.
The 50 watt directly heated white hot tungsten cathode in the output valve glowed brightly enough to read a newspaper.
If the 1/8" thick carbon anode started glowing red hot I knew to reduce power.
I had a mere 2000 volt H.T. supply so I can't be sure the valve would have survived arcing between electrodes...

The circuit supplying power to the heater was separate from the signal the tube was acting on. This is why older radios and TVs used to have to warm up before they would start working. (one scheme used to get around this was to have the heater circuits of the tubes "on" all the time even when the device was off, thus the tubes were ready to go the moment you turned it on.)

'New' mains powered radios had a long warm up time. Older battery powered radios had directly heated cathodes which warmed up almost instantly.

The same thing happened with transistors. Initially they were 'instant on.' Now somewhere in tv adverts' small print for 'smart' devices there's always a 'sequence shortened' warning. You can instead leave the device "on" all the time and find the battery flat if you've left it too long.

I worked on an early British mobile phone which had a (very) quick heat output valve to reduce the size of the optional battery pack for portable use away from a car battery.
The police liked it as well since you just had to connect a loudspeaker to a winding on the modulator transformer to have a powerful P.A. system.

 

Happy days...

[studiot]

Lovely post, Carrock. +1

 

But would someone please remind me what the actual OP question was?

[Strange]

Lovely post, Carrock. +1

 

But would someone please remind me what the actual OP question was?

Remind? Or explain?

[swansont]

"I remember seeing an illustration of a vacuum tube. It had a battery/ power supply connected to the VT. The VT conducted electricity and then sent signals throughout the

computer."

I think your memory may be letting you down.

The only VT I ever saw in a computer was the CRT screen.

 

 

You may just not be old enough, or haven't delved into the relevant history

https://en.wikipedia.org/wiki/List_of_vacuum_tube_computers

[OldChemE]

OK-- I think I see what the OP's question is-- If I'm wrong, forgive me.

 

I think the question is why did we need Vacuum tubes (and later transistors).

 

Prior to the digital revolution, all signals were analog. This included radio and TV. radio/TV signals as received from the air are very weak, and have to be amplified. That was the function of the Vacuum tubes and later transistors-- amplification. Specifically, a small analog signal on the input could be made to produce a duplicate signal with larger voltage swing at the output. Thus, the purposes of these devices was not to transmit voltage to the screen or speaker, but to raise the magnitude of the signal to make it strong enough to drive the speaker or output device. Many modern devices don't require the high voltages so this function is becoming less common.

[swansont]

Put another way, there's a whole bunch of technology you can develop when you aren't limited by Ohm's law.

[Endy0816]

Indeed. So I'm not sure about John's comment. There were valve-based computers and so it is possible that Elite Engineer has read something about them.

 

 

Thanks for that.

 

Welcome.

 

Have to admit my own understanding of them is pretty abstract. Found this thread an interesting read.

 

 

I always liked thermionic valves, not least because you could actually see inside them and sometimes diagnose a dodgy valve by visual inspection.

So a defence....

Inefficient, certainly. AFAIK, magnetrons are still used in domestic microwave ovens.

Producing a few hundred watts at 2.45 GHz from a solid state device is still not cheap and it's hard to protect a solid state device from all the possible loads in a cooker.

Producing high power at high frequency, and the CRT, were the last holdouts against solid state devices.

 

However valves are much slower to die when you maltreat them.

I used to have an ancient A.M. transmitter with an ex battleship power supply that required four people to carry it.

The 50 watt directly heated white hot tungsten cathode in the output valve glowed brightly enough to read a newspaper.

If the 1/8" thick carbon anode started glowing red hot I knew to reduce power.

I had a mere 2000 volt H.T. supply so I can't be sure the valve would have survived arcing between electrodes...

 

'New' mains powered radios had a long warm up time. Older battery powered radios had directly heated cathodes which warmed up almost instantly.

 

The same thing happened with transistors. Initially they were 'instant on.' Now somewhere in tv adverts' small print for 'smart' devices there's always a 'sequence shortened' warning. You can instead leave the device "on" all the time and find the battery flat if you've left it too long.

 

I worked on an early British mobile phone which had a (very) quick heat output valve to reduce the size of the optional battery pack for portable use away from a car battery.

The police liked it as well since you just had to connect a loudspeaker to a winding on the modulator transformer to have a powerful P.A. system.

 

Happy days...

 

Does seem like a more interesting time to be alive(although I do appreciate having computers that can sit in the palm of my hand too).

[studiot]

Well I still have no real idea what the OP meant, but here are some thoughts.

 

Storage (memory) is arguably the most important element of electronic (and even non electronic) computers.

All those ones and noughts are totally useless if you cannot organise them, store them until you want them and then retrieve them.

Pretty well every computer chip or module built of discrete components (semiconductor or vacuum tube) contains some form of storage.

 

In order to perform these functions you require pulses and to generate these pulses you require active devices - that is semiconductor or vacuum tube devices.

 

Most modern computer memory has to be 'refreshed' many times a second or the stored information leaks away.

Again pulses are required.

[Janus]

Another thing that the OP might not be aware of is that even logic gates require an external power source other than the input signals in order to operate.

[Sensei]

Why do we need vacuum tubes

 

Let me explain how vacuum tubes can work.

In vacuum tube there is positive electrode, which accelerates free electrons,

and negative electrode, which has abundance of electrons.

There can be used light, IR, visible, or UV, or x-ray, or gamma photons, to eject these electrons.

f.e using photoelectric effect on negative electrode.

https://en.wikipedia.org/wiki/Photoelectric_effect

or thermionic emission

https://en.wikipedia.org/wiki/Thermionic_emission

to accelerate rate of creating new free electrons on hot cathode

https://en.wikipedia.org/wiki/Hot_cathode

Once they are ejected, they cannot go back to negative electrode (because it's repelling them),

so they are accelerated toward positive electrode.

If there is nothing else done, electrons are hitting positive electrode, decelerate, emitting photons to conserve energy, and go by wire.

However, if there is hole in positive electrode, and there are used magnets/electromagnets, which bend their trajectories, electrons fly through hole.

And such device we call electron gun.

https://en.wikipedia.org/wiki/Electron_gun

 

Then they fly through vacuum, and hitting 2nd side of vacuum tube ("screen").

If it's made of fluorescent material, after hitting it by free accelerated electrons, photons in visible range are created (otherwise there are made UV/x-rays).

To capture UV/x-rays there is used thick lead glass

https://en.wikipedia.org/wiki/Lead_glass

https://en.wikipedia.org/wiki/Radiation_protection

(to protect human behind screen)

 

If nothing is done to electrons, you will get single spot on screen.

To bend trajectory there can be used external electric field (abundance of electrons on one side, and absence of them on second side), or external magnetic field (electromagnet, true magnet, superconducting electromagnet).

So, if you want to current go from AB or AC, where A is cathode and B and C are anodes, you can control trajectory of electrons toward B, or toward C, by controlling current flowing by wire of electromagnets in vacuum tube (2nd side), or creating high voltage on electrodes in vacuum tube (2nd side).

Edited June 20, 2017 by Sensei

[Elite Engineer]

OK-- I think I see what the OP's question is-- If I'm wrong, forgive me.

 

I think the question is why did we need Vacuum tubes (and later transistors).

 

Prior to the digital revolution, all signals were analog. This included radio and TV. radio/TV signals as received from the air are very weak, and have to be amplified. That was the function of the Vacuum tubes and later transistors-- amplification. Specifically, a small analog signal on the input could be made to produce a duplicate signal with larger voltage swing at the output. Thus, the purposes of these devices was not to transmit voltage to the screen or speaker, but to raise the magnitude of the signal to make it strong enough to drive the speaker or output device. Many modern devices don't require the high voltages so this function is becoming less common.

Yes, this was spot on. I was thinking..why have a power source power your vacuum tubes to power your computer..but the vacuum tubes (and later transistors) don't actually "supply" power, but provide/ amplify signal. Right?

Many modern devices don't require the high voltages so this function is becoming less common.

So transistors and later IC's require less voltage because they're smaller?

 

Vacuum tubes used high voltages which would fry the logic gates if the power source was hooked up to the computer directly. Vacuum tubes of the time were also rectifiers in that they could convert an alternating current radio signal into direct current which could then be used to record music onto tapes/records.

so the vacuum tubes supplied power to the logic gates, or the tubes were the logic gates?

[studiot]

Another thing that the OP might not be aware of is that even logic gates require an external power source other than the input signals in order to operate.

 

 

Diode - Resistor OR gates required no power source and were used in early logic boards.

[Janus]

Yes, this was spot on. I was thinking..why have a power source power your vacuum tubes to power your computer..but the vacuum tubes (and later transistors) don't actually "supply" power, but provide/ amplify signal. Right?

So transistors and later IC's require less voltage because they're smaller?

so the vacuum tubes supplied power to the logic gates, or the tubes were the logic gates?

 

Vacuum tubes and transistors, "amplify" signals by using a low voltage signal to control a larger voltage to make a higher voltage "copy" of the input signal. They still need that external voltage source to work.

 

Transistors can use lower voltages due to the way they work, IC's just contain an equivalent circuit to one built from discrete components printed on a single substrate. For example, here's a diagram for a 741 Op-amp IC. It includes transistors, resistors, etc, all printed onto a single silicon chip.

 

Vacuum tubes were used to make the gates. (In addition, vacuum tubes of the diode type were lprobalbly used to convert the AC line voltage to the DC needed to operate the gate circuits properly. They didn't supply the voltage as much as help covert it to a more usable form.)

Edited June 21, 2017 by Janus

[John Cuthber]

 

Indeed. So I'm not sure about John's comment. ...

I was in a hurry,

The only VT I ever saw in a computer outside of museums was the CRT screen.

In principle, you can go even more "old school" and use relays.

You would need a dedicated power station to run the equivalent of a small computer, and I don't know how you could keep it cool.

It would also be something like a billion times slower.

 

I'm still not sure what question the OP was asking.

Edited June 22, 2017 by John Cuthber

[Elite Engineer]

I was in a hurry,

The only VT I ever saw in a computer outside of museums was the CRT screen.

In principle, you can go even more "old school" and use relays.

You would need a dedicated power station to run the equivalent of a small computer, and I don't know how you could keep it cool.

It would also be something like a billion times slower.

 

I'm still not sure what question the OP was asking.

I thought that VT's were meant to power the computer...but now I know they're to produce a signal, (i.e. 1's,0's)

[Joatmon]

Question asked - Why even have the power source (wall outlet basically) connected to the VT, and just hook up the power source up to the computer directly,

 

Simple Answer. Wall sockets provide relatively high voltage alternating current, computers run on low voltage direct current, as do most electronic circuits. You need something to reduce the voltage (a transformer) followed by something to change the alternating supply to direct current ( a rectifier). The rectifier back in the 1960's would have used one or more vacuum tubes (thermionic diodes). With the coming of transistor technology the diodes would be replaced by semi-conductor diodes (PN junctions). Later still the development of silicon based devices such as transistors and microchips allowed ever more complicated circuitry to be developed that would hold the low voltage circuit supply steady under different loads and a range of input voltage. We now call a package that contains the three elements(voltage reduction. rectification, stabilisation) a power supply. It usually is a small black box that sits between your wall socket and your computer.