The Tube Computer
A modern 8 bit design, built with recycled 1950s vacuum tubes, that glow and heat the entire room.
After a ridiculous amount of soldering,
and a fantastic amount of fun.
The Tube Computer stands on a wall in our home,
and is almost safe to touch.
Almost!
Vacuum Tubes require high voltages to work efficiently and are not for the faint hearted. They can switch several hundred million times a second, and in the 1950s they were combined with germanium diodes as the basis for many incredible computer designs.
The Tube Computer has a modern 8 bit architecture. It is designed to run a simple airship flight sim, flying around Brighton for the grandchildren, or a 64 bit Fibonacci sequence for the grown ups.
Building tube computers has become an addiction, this is my third! The first ran on 28th May 2021 whist perched on our dining room table, chairs and surrounding floor space. A fairly harmless addiction, I suppose!
After switch on you have to wait a while for the vacuum tubes to warm up. If you look from the side you see them start to show a red glow. After about a minute The Tube Computer has a pleasant homely aroma from the hundreds of double triodes, all quietly burning off their dust.
The Tube Computer is still a work in progress, and live adjustments are often required. It takes about 10 minutes to thermally stabilise, then a last few tweeks, check the fire extinguisher is full, and run the software.
The Human Form, a Waving Hand and Family
The Human Form
Is is just me, or does The Tube Computer look Humanoid?
The shape evolved naturaly from the function.
I wanted all the boards associated with the Arithmetic Logic to be located together, which led to a long lower section.
The middle was to deal with all the control functions and the top was for the input, output and registers.
The side bits grew as I had only allowed 1 board on the left for the clock system, which became 5, and the same for the Vacuum Tube RAM, which grew to 5 boards on the right.
I keep checking it has not walked out of the room!
Hand Waving
Doing my best to explain how my previous tube computers worked involved a lot of waving of my hands around groups of hot vacuum tubes and then the scribbling of a few boring drawings.
This time I wanted my grandchildren to be able to actually see it work, with maybe just a bit of hand waving, but absolutely no scribbling.
I designed The Tube Computer so it could show itself working at the most fundamental level of computing, the instruction cycle, and how, after many, many simple data manipulations they combine to create the power of a personal computer.
A great big, very hot, and slightly dangerous, personal computer.
Family
My family was homeless when I was born. But my parents found work, the council found us a flat, and 20 years later my dad was the managing director of a very large engineering firm, and my parents built a fabulous home.
To cut a long story short, much later my parents had a few personal problems, and sadly my mum finally killed herself. I don’t think you ever get over it, you really just learn to live with it.
My life then went a bit pear shaped. I trusted bad people and guess what, really bad things happened. Very kind friends managed to put me back on my feet, and then, at 55, I met Judy and her family, and we’ve had the most wonderful 15 years together.
So please, what ever happens, please don’t give up.
Tube Computer Video
This is a descriptive, non technical, 12 minute video and outlines most of The Tube Computer components.
On reflection I do harp on a bit, and perhaps it should have a serious content warning:
“May contain scenes of Mike wittering on, which some viewers might find inept”☺
The Why, The IBM700, and The Architecture
The Why
After visiting Bletchley Park, it occurred to me that several Tube Computers had been rebuilt, and now run in museums, but that no new models had been constructed for over 50 years. The thought of building one seemed ridiculous, but I wondered if a modern design could overcome the issues of size, power and the very real danger of high voltages.
When I retired I rediscovered the adventure. But my most important discovery is that building stuff is a great way to learn.
The IBM700
The IBM700 series was the most successful 1950s computer system. A very sophisticated design, it combined more than 1,700 tubes with 4,600 germanium diodes on hundreds of plug-in modules. Able to handle 36 bit words using 18 bit instructions, it could be rented for $12,000 a month.
The Tube Computer is slightly cheaper, and is constructed from recycled 6N3P tubes and IN33A germanium diodes both introduced in the 1950s, combined with new resistors and capacitors on plug-in modules.
Architecture
Initially I tried various architectures with different types of gates, but they all became too intricate, and I failed to remember to “keep it simple, keep it clean”. Eventually I made a design only using NOR gates. This made it really interesting, as the ALU and binary counters had to be designed with just NOR gates, which was fun!
I recently discovered that a few incredibly important computers had designs based entirely on NOR gates. I wish I’d known that earlier!
Airship Simulator
I wrote this software for my grandchildren. The basic idea is that back in the 1920s the commercial development of the British R80 airship had actually been approved by the government and the Airship is moored overnight at the wonderful Brighton Aerodrome before a morning launch on a voyage to Paris. What fun that would be! I do wish somebody would be foolish enough to organise this voyage for real, Judy and I would be first in the queue for tickets.
By pressing controls on the image of the bridge of the R80 you can direct the airship software. These membrane buttons simply put 5 volts directly to the input board of The Tube Computer. You can control the ballast, gas release, engine power, elevators, rudder and the bow mooring gear, which is used to release the airship from the tower.
You do need a bit of vision, but it’s lovely to imagine flying over the old West Pier in the airship and then a leisurely cruse along the sea front on the way to France. The airship’s location is generated every few seconds by The Tube Computer and using the status system the X, Y, and Z values would be shown on this panel.
[A work in progress]
[Console]
Unfortunately the console’s design is far too simple.
I hoped to have 0 and 5 volts logic levels everywhere, but in practice, it is just not possible, and the display console can’t cope with the reality of some of these wide level variations.
It needs a complete redesign, maybe incorporating Schmitt triggers with some clever signal averaging but I also thought a second generation console could be made quite colourful.
[Status]
I should have The Tube Computer permanently connected to multiple inputs and outputs and use the [STATUS] instruction to select a single IO device. It should enable 3D to be sent as the three X, Y, Z values to the flight sim panel and 64 bit data could be transferred in 8 blocks between computers.
The status system is still a work in progress and it’s just one input and one output at present. So no flight sim yet!
[Step ladder]
The tube computer does require continuous tweeking. It is probably one of the few computers that needs both a small tweeker and a big step ladder!
I should have added more buffers to the design to isolate controls from their functions, so that the setup would be far less critical.
Although a real bonus is that the step ladder keeps me fit!
Build it now, Fix it Later
The Tube Computer is a once in lifetime project for me, so I decided not to do a “build a few bits and see what happens” version.
Which reminds me, the ducks on the pond needed a lighthouse, as it is sometimes difficult to see the edge of the pond. I thought I would help, and after discussing it with no one, I just built a lighthouse. Just doing it is far more fun than planning and project managing, the only problem is the quality of the result.
It was not even watertight, and a bit of a family joke, and so it went into the shed.
I decided to build a second one.
This time I had a plan.
Plan it now, build it later
Project management is not just a tool to mislead the client into thinking you're actually doing something. It can also be used to create a high quality product, on time, and always just slightly over budget!
For the second lighthouse I project managed, designed and then 3D printed all the parts, It looks great, and fits the brief completely. But guess which one I now prefer.
So two lighthouses later, I realised that the act of planning sometimes loses the spirit of the idea. Even so, I decided to try to plan and manage The Tube Computer build as one entire project.
It is still a work in progress, and do I wonder which version of the lighthouse it will finally become.
Tube Computer Project
My stepdaughter is a senior Product Manager and my stepson is a Chartered Engineer and he frequently works as a Project Manager. They would know how to manage this project. Luckily they are too successful and busy to ever read this, thank goodness!
I tried doing the project management on a PC but gave up, and instead used 3 coloured pens, A4 paper and self adhesive address labels to cover up my mistakes. I simply found it easier. The only problem I discovered is that the paper gets a bit thick after several layers of amendments, but the big advantage is that can always find your latest version, it's simply the thickest.
The main thing I discovered was that the first time I tried almost anything I failed, but the annoying experience often enabled future success.
I first started by stabbing at various bits of the idea. Eventually I was able to define what I wanted to do. I now realise that this definition, was the most important part of the whole project management!
The program seemed to consist of many complex components, all of which I needed to understand, to be able to build The Tube Computer.
How do thermionic vacuum tubes work, how do you design a PCB, and how on earth do you get from a NOR gate, to a memory register, via microcodes from a clock, binary counters, and a ROM, to actually run software. And what exactly is a microcode anyway. At times, in fact most of the time, it all just seemed impossible.
The main solutions I found were, firstly to keep the number of unique sub systems to an absolute minimum. Secondly to use double triode tubes to halve the physical size, which also reduced the construction time. And thirdly, to design multi layer printed circuit boards to reduce the inevitable build errors and produce a robust construction.
The Tube Computer has behaved itself so far, unlike a previous system that went BANG twice. The first time I pulled out plugs like my life depended on it, and Judy cried, “Everything all right!”. The second time I only slightly panicked, and Judy continued to decorate the Christmas tree, but later bought me a surprise present, a fire extinguisher!
But most important of all, is to have a lovely wife, who knows you're daft as a brush, and that life together is brilliant.
Best wishes, Mike and Judy.