The Fred.Computer


A New Vacuum Tube Computer.

A modern 8 bit design, built using 1950s thermionic valves  that glow and heat the entire room.


The prototype first ran on 28th May 2021 whist perched on our dining room table, chairs and surrounding floor space.

The Fred.Computer is now firmly nailed to the study wall,

and is almost safe to touch.



Thermionic valves, (aka vacuum tubes), can switch several hundred million times a second, and in the 1950s were the basis for all computer designs. To work efficiently they require high voltages and are not for the faint hearted.


The Fred.Computer is an 8 bit computer, with the usual 12 bit address and data buses plus the rather unusual current demand of over 200 Amps. It can play a decent game of PONG using its world speed record relay RAM, or run a 32 bit Fibonacci sequence using modern NVRAM.

After switch on you have to wait a while for the last thermionic valve to warm up. If you look from the side you see a few start to show a red glow. After about a minute the Fred.Computer has the pleasant homely aroma of 560 double valves, quietly burning off their dust.

When all the valves are glowing, I check the fire extinguisher is full, and run the code.


The Fred.Computer.

The Fast Reliable Electronic Digital Computer.

A new thermionic valve computer for the 21st century.


It has been a ridiculous amount of soldering and a fantastic amount of fun.

The Why, The When, and The Where

After visiting Bletchley Park, it occurred to me that several thermionic valve computers had been rebuilt, and now run in museums, but that no new design of a valve computer had been constructed in 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 looked at the problem again and realised it could be an interesting  endeavour. I spent an enjoyable 18 months building both the prototype and the Fred.Computer.


To rapidly construct the 8 main boards of the Fred.Computer I modified the prototype PCBs which required changing over 1,000 components. The rebuilt main boards are now configured exactly as shown in the technical page schematics. There are also new auxiliary valve boards incorporating additional registers and modified oscillators.


The new system console incorporates the GUI from the prototype, and a new RAM, the world's fastest relay RAM. The novel 700Hz design is sadly very quiet, so I have now added a sound port and speaker!


I found it best not to use a separate room to build the computer, but to spread it all over the house, one bit in each room if I could, just so I knew where everything was. To my great surprise my lovely wife Judy was completely overjoyed when after only a year or so, I transferred all the components around the house onto the study wall.


Please note that high voltages are very dangerous and shouting bang when a friend has their back to the computer is very childish, but great fun. I must stop doing it!

A Warm Glow


The Fred.Computer is designed using 1,120 thermionic triodes. Conveniently each 6N3P valve contains 2 triodes around a single heater, halving the physical size and power requirements.

All the double valves are configured as identical NOR gates. The registers are built from groups of 5 NOR gates, and combined into D type flip flops. The NOR gates also form all the other functional components, including the 8 bit ALU, the two oscillators, and the relay drivers.

The amount of heat is ridiculous, but the warm cosy aroma is divine.

The Turner Prize


The Fred.Computer integrates eight large printed circuit boards and four auxiliary PCBs, which combine the thermionic valves into a functional computing system. The Graphical user interface, a diode matrix ROM, and a reed relay RAM complete the magic to collectively become an 8 bit, thermionic valve, general purpose computer.


It has now grown beyond its design, and for me, has become an art installation on the study wall.


Every one agrees that the Turner Prize is much more than just a display of virtue signalling by the cultural elite, and I have decided to enter the Fred.Computer for the prize.


I shall write about the blank canvas of machine code, the brush with danger, the sculpture of the valve, and a palette load of arty stuff like that. I am sure Tate Modern will be impressed!

Polyonymous Triodes, a new Console, and no Safety Net

Thermionic valves (or just valves) in the UK, are also named vacuum tubes (or just tubes) in the USA, and электронная лампа (or just electron tubes) in Eastern Europe. The 6N3P thermionic valve was produced in many communist factories in the 1950s and 1960s.

The finest 6N3P thermionic valves were selected at manufacture for military use, with up to 5000 hours life expectancy and printed with an additional code (Cyrillic 6Н3П-ЕВ). The rest were for domestic use, and with the ability to operate at over 210Mhz, the 6N3P was used in many 1960s East European VHF radios, televisions and in several beautiful radiograms.

The Fred.Computer has a new system console, which lifts open from the front.

Five AZTEC MP6 PSUs are now behind the Console. These second hand, 60 Amp professional power supplies replace the prototype's cheap and cheerful PSUs. It turns out that cheap PSUs do not like a metal inspection torch across their unprotected outputs.

The AZTECs enable the heaters to have a soft start, which hopefully will extend the life of the thermionic valves and I now use a plastic inspection torch.


Fred.Computer programs are written using just 16 instructions. Machine code is real code, a totally different world to all the posh high level languages. It's gloves off with no safety net. You simply talk directly to the computer. It is incredibly fast compared to other programming languages, and gives you control over data storage, memory, and computer hardware. It can be a very useful tool in fast decryption and modern graphics. It's use may give a deeper understanding of  high level coding, but really it's just great fun.

Henry's Fibonacci Sequence Video


On 15th August 2021, three months after the first table top run with manual ALU computation and storage, the prototype for the new Fred.Computer demonstrated a clocked, GUI displayed, 8 bit Fibonacci sequence.

The Fibonacci value is displayed vertically, in binary. It uses both the GUI relay memory and NVRAM, and is demonstrated by Henry the cat.

Judy's PONG Game Video


On 11th January 2022, Judy starred as the Mysterious black gloved lady, in the epic video production of  The PONG Game. Using the prototype for the new Fred.Computer, she demonstrated a simple version of the game.

Less than 100 machine code instructions enable the ball to bounce around the court, and subroutines for gameplay and the GUI display complete the program.

It's is a fast, action packed, no holds barred game [NOT].

Spoiler alert, the final score is ONE - NIL, but guess who wins!


The Fred.Computer is named in honour of my hero. Fred was born in 1927, the 8th member of his family living in rooms in a run down part of London. The pre-war slums of the city were tough.

He was evacuated to rural Surrey at the start of the war, but his parents could not afford the weekly 5 shilling fee and Fred had to return to the bombings in London.

Leaving school at 13 he found work in a saw mill, as the feed assistant on an incredibly dangerous swing saw. He managed to retain all of his fingers and was called up for National Service just after the war.

He rose to the rank of Warrant Officer Class 1 [Sergeant Major].

Returning to civvy street he married Ena and soon she was with child. They found furnished rooms in a small house but when her pregnancy became obvious they were forced to leave. The council put them into in a homeless hostel, the old Swaffield Road workhouse, (since renamed Brocklebank, it now even has a blue plaque!).

Being homeless was not the end for our family, it became a new start. Ena found the other residents to be extremely kind, and I acquired a brand new Pedigree pram. Fred was working long hours in the saw mill, where one day the foreman was suddenly sacked. Fred was going on an Army exercise after work and was wearing his Warrant Officer Class 1 uniform, the boss turned to him and made him the new foreman.

We were moved to a council flat and I had my own bedroom, it was incredible.

Next to the Saw Mill was a very large toy factory, Fred identified it as his future and took a pay cut to became a chargehand at the company.

Within a few years Fred had become a junior manager, then Works Manager and finally the General Manager. He was never in his office, but could always be found on the shop floor of the massive factory. It had the largest injection moulding shop in Europe and I had never seen so many toys.

Ena and Fred both worked long hours to get a mortgage and buy a house. Fred took up the post of Works Director of an Engineering firm near their new home.

He became a Chartered Engineer and Fellow of the Institute of Mechanical Engineers. They moved to the Midlands and Fred became the Managing Director of a large Engineering company where he introduced the new DEC PDP-11 computer and still found the time to manage the build of their future home. It was a fast paced incredible career.

But what he really does is to help and guide everyone in his extended family. He makes the time to be there when needed, somehow making everything alright again. He has enabled many friends and family members achieve their aspirations and fulfil their dreams. He encourages many, has saved a few, and always gives everything.

The Fred.Computer is named in honour of my amazing Dad.