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Question About Transistors vs Vacuum Tubes

 
 
Reply Wed 6 May, 2020 06:22 pm
I need to ask a question of someone who knows electronics much better than I do. Is there any digital circuit made with transistors, for which vacuum tubes would simply not work, if size, convenience, power, and reliability were not issues?

Yes, I know it's impractical. This is an abstract question.

Thanks.
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Type: Question • Score: 0 • Views: 580 • Replies: 14
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maxdancona
 
  1  
Reply Wed 6 May, 2020 06:32 pm
@Brandon9000,
You didn't have time on your list of criteria.

Semiconductor transistors are much faster than vacuum tubes.
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maxdancona
 
  1  
Reply Wed 6 May, 2020 06:37 pm
@Brandon9000,
You will have to define what "digital circuit" means. If you are talking about logic gates and memory, then I would say the answer is that anything can be replicated with vacuum tubes.

I just checked if solid state RAM could be replicated by vacuum tubes (this question interests me). The answer is yes.... but it would be very expensive and slow.
Brandon9000
 
  1  
Reply Wed 6 May, 2020 07:16 pm
@maxdancona,
I don't know much about this, but I mean like a counter or comparator or something.
edgarblythe
 
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Reply Wed 6 May, 2020 08:08 pm
Who uses vacuum tubes? I thought they had gone extinct.
maxdancona
 
  1  
Reply Wed 6 May, 2020 08:11 pm
@Brandon9000,
I am curious about your interest in this topic.... this might make an interesting plot device for a science fiction story.

Digital circuitry is based on logic gates. There are basic gates "AND", "OR", "NAND", "NOR", "NOT" ..... etc. Actually (this is nerd trivia) all of these gates can be created with only NAND gates I don't know if this is interesting). If you can make a NAND gate, you can make any digital circuit found in any digital device of computer (of course there are much more efficient ways to do things).

If you can make these logic gates, then you can make more complex digital circuits including counters, comparators ... or anything else you need. The computer you are using is built on these basic logic gates.

1. Yes, any of these can be made with vacuum tubes.

2. There are other analogs for these gates... which have been made with legos and tinker toys. In a local museum, I have seen a tinker toy machine made only with wooden pieces rubber bands and string that plays tic-tac-toe perfectly (it never loses).

3. Any time you can make these basic logic gates, you can make any digital circuit. One of my favorites is inside the game MineCraft (a brilliant game on any level). In side the game you can build "redstone devices" that can be turned into AND, OR and NAND gates. So you can build working digital circuits inside the fictional universe of the game. People have built fully functional digital calculators inside the game.

Of course, the designers of the game knew exactly what they were doing. It is very cool.
Brandon9000
 
  1  
Reply Wed 6 May, 2020 08:42 pm
@maxdancona,
maxdancona wrote:
I am curious about your interest in this topic.... this might make an interesting plot device for a science fiction story....

Actually, that's what it is, but I don't want to say anything about that. I'm actually looking for a type of circuit that can't really be duplicated well with tubes, and not merely because it uses a lot of transistors.
Brandon9000
 
  1  
Reply Wed 6 May, 2020 08:45 pm
@edgarblythe,
edgarblythe wrote:
Who uses vacuum tubes? I thought they had gone extinct.

Not to be mean, but read the question. This was abstract curiosity. And, by the way, vacuum tubes are still occasionally used in very high power circuits.
engineer
 
  1  
Reply Wed 6 May, 2020 08:52 pm
@Brandon9000,
The US discovered the Soviet MIG 25 used vacuum tube technology.

https://en.m.wikipedia.org/wiki/Mikoyan-Gurevich_MiG-25
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maxdancona
 
  1  
Reply Wed 6 May, 2020 09:01 pm
@Brandon9000,
Cool. I hope I get the chance to read it.

Any digital computer (based on binary on/off signals) works with these basic logic gates. When you take a digital circuits class, you start with these gates, then you use them to build little circuits called "flip-flops" and from there you build counters, accumulators, comparators, etc.

This is the way it it has worked since vacuum tube computers. The basic logic gates haven't changed. What has changed is that we have figured out how to pack millions of these logic circuits (counters, accumulators, compactors) into very small semiconductors. But the basic building blocks haven't changed.

There were some experiments done with analogue computers (where the signal was a level rather than binary on/off). As far as I know these never had any use outside of a few very specific applications.

But to answer you question. Vacuum tubes use the same basic building blocks that are used on semiconductor circuits... and so, theoretically if you have infinite money space power and time, you could build any circuit using vacuum tubes.

One measure of hope fast a computer works is in "FLOPS". FLOPS stands for "floating point operations per second" and you can think of this as how many pairs of numbers it can multiply in a second. "The ENIAC (a very powerful vacuum tube computer) ran at 500 FLOPS.

Your typical cell phone can handle 1,000,000,000 FLOPS (that is a billion). So yeah, getting any result on your vacuum tube computer is going to take a lifetime.




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Brandon9000
 
  1  
Reply Wed 6 May, 2020 09:13 pm
Then a circuit made from tubes which needs to perform repeated operations couldn't run at as high a speed as with transistors?
maxdancona
 
  1  
Reply Wed 6 May, 2020 09:33 pm
@Brandon9000,
Brandon9000 wrote:

Then a circuit made from tubes which needs to perform repeated operations couldn't run at as high a speed as with transistors?


Exactly... and it is difficult to exaggerate the difference. Your cell phone (assuming you bought a normal smart phone in the past 5 years) can literally do millions of calculations in the time it took the best vacuum tube computers (that took up the floors of universities) to do one.
Brandon9000
 
  1  
Reply Wed 6 May, 2020 09:37 pm
@maxdancona,
Then I have what I need, a use for which vacuum tubes won't work. Thanks for all the time you spent on this.
0 Replies
 
maxdancona
 
  2  
Reply Wed 6 May, 2020 09:42 pm
@maxdancona,
It might be interesting to you that when you are designing semiconductors... the speed of light matters. You see, electrical signals can't go faster than the speed of light. So, if you double the length it has to go you double the time it takes to get there. Modern digital circuits are designed to go fast enough that this time matters.

People who design computer chips work hard to make sure the most important circuits are jammed close together. That way the signals only have to travel a very short distance (i.e. microns).

Computer pioneer Grace Hopper (who truly was brilliant) used to hand out "nanoseconds"... little pieces of wire (11.8 inches long) that represented the maximum distance that electricity could travel in one billionth of a second.


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oralloy
 
  1  
Reply Thu 7 May, 2020 05:41 pm
@edgarblythe,
edgarblythe wrote:
Who uses vacuum tubes?

My dad's antique jukebox uses them.


edgarblythe wrote:
I thought they had gone extinct.

He can order spare tubes from some kind of Russian manufacturer.
0 Replies
 
 

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