# \#vacuum-tube **URL:** https://scanalyst.fourmilab.ch/tag/vacuum-tube/300.md [Latest](https://scanalyst.fourmilab.ch/latest.md) · [Categories](https://scanalyst.fourmilab.ch/categories.md) · [Tags](https://scanalyst.fourmilab.ch/tags.md) --- ## [Powering Up a 1950s Bendix G-15 Vacuum Tube Computer](https://scanalyst.fourmilab.ch/t/powering-up-a-1950s-bendix-g-15-vacuum-tube-computer/4146)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [28 December 2023 14:09 UTC](https://scanalyst.fourmilab.ch/t/powering-up-a-1950s-bendix-g-15-vacuum-tube-computer/4146 "2023-12-28T14:09:41Z")
When you have a half tonne computer containing 450 vacuum tubes and a magnetic drum memory spun at 1800 RPM by a big AC induction motor, just turning on the power is an exciting event. The Bendix G-15, int… --- ## [Vacuum Tube Computer Part 35: Output Register—a One-Byte Write-Only Memory](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-35-output-register-a-one-byte-write-only-memory/4090)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [11 December 2023 13:12 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-35-output-register-a-one-byte-write-only-memory/4090 "2023-12-11T13:12:13Z")
Output from the one-bit vacuum tube computer is sent to an 8-bit addressable output register, where it is stored and can be sent to external devices. Since the output register cannot be read by the compute… --- ## [Inside the Bendix G-15's Magnetic Drum Memory](https://scanalyst.fourmilab.ch/t/inside-the-bendix-g-15s-magnetic-drum-memory/3793)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [26 September 2023 13:24 UTC](https://scanalyst.fourmilab.ch/t/inside-the-bendix-g-15s-magnetic-drum-memory/3793 "2023-09-26T13:24:01Z")
The Bendix G-15 vacuum tube computer used a rotating magnetic drum for its main memory. Except for a few registers internal to the processor, all system memory was kept on the drum, as described in the 202… --- ## [Vacuum Tube Computer Part 34: Paper Tape Interface and Clock Generation](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-34-paper-tape-interface-and-clock-generation/3758)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [18 September 2023 14:31 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-34-paper-tape-interface-and-clock-generation/3758 "2023-09-18T14:31:03Z")
With the decision to supply instructions (operation codes and address fields) to the one-bit vacuum tube computer from paper tape (making it run similarly to the original IBM Card-Programmed Electronic Calc… --- ## [Origin of the Cavity Magnetron](https://scanalyst.fourmilab.ch/t/origin-of-the-cavity-magnetron/3669)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [29 August 2023 12:21 UTC](https://scanalyst.fourmilab.ch/t/origin-of-the-cavity-magnetron/3669 "2023-08-29T12:21:09Z")
Here is more about the cavity magnetron. Curiously, the first magnetron (not yet using a cavity resonator) was invented by Albert W. Hull of the General Electric Research Laboratory in the early 1920s as a… --- ## [Vacuum Tube Computer Part 33: Input/Output Address Decoding](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-33-input-output-address-decoding/3541)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [31 July 2023 13:10 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-33-input-output-address-decoding/3541 "2023-07-31T13:10:12Z")
Data input and output for the vacuum tube computer uses three registers, each with individually addressable bits accessible from the processor: input, output, and scratch. Each register contains eight bits… --- ## [Inside a 1950s Vacuum Tube Computer: Bendix G-15](https://scanalyst.fourmilab.ch/t/inside-a-1950s-vacuum-tube-computer-bendix-g-15/3499)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [24 July 2023 12:11 UTC](https://scanalyst.fourmilab.ch/t/inside-a-1950s-vacuum-tube-computer-bendix-g-15/3499 "2023-07-24T12:11:21Z")
Restoration of the Bendix G-15 vacuum tube computer with magnetic drum memory begins by removing all of the circuit boards, removing the dust and grime of the ages, inspecting each for the usual problems of… --- ## [Vacuum Tube Computer: Calamity and Reconstruction](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-calamity-and-reconstruction/3404)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [4 July 2023 13:14 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-calamity-and-reconstruction/3404 "2023-07-04T13:14:01Z")
There are many mishaps one can imagine befalling a vacuum tube computer: catching fire from all the heat emitted, catastrophic cascading electrical failures, intermittent errors due to power supply and grou… --- ## [Vacuum Tube Computer Part 31: Rethinking the Design, Enter Paper Tape](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-31-rethinking-the-design-enter-paper-tape/3363)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [25 June 2023 16:05 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-31-rethinking-the-design-enter-paper-tape/3363 "2023-06-25T16:05:11Z")
When you’re building a computer from vacuum tubes, thinking as one has become accustomed to in the era of cheap and abundant semiconductor memory can end up with massive banks of tubes doubling as a space h… --- ## [Unboxing a 1956-Vintage Bendix G-15 Vacuum Tube Computer](https://scanalyst.fourmilab.ch/t/unboxing-a-1956-vintage-bendix-g-15-vacuum-tube-computer/3334)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 1\ **Last updated:** [23 June 2023 15:49 UTC](https://scanalyst.fourmilab.ch/t/unboxing-a-1956-vintage-bendix-g-15-vacuum-tube-computer/3334 "2023-06-23T15:49:33Z")
The Bendix G-15 has been called the first personal computer. Despite weighing around half a tonne, using 450 vacuum tubes, consuming around five kilowatts of electricity, and costing about half a million 2… --- ## [The Birth of Electronics—from the Incandescent Lamp to Digital Logic](https://scanalyst.fourmilab.ch/t/the-birth-of-electronics-from-the-incandescent-lamp-to-digital-logic/3175)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 5\ **Last updated:** [4 June 2023 00:24 UTC](https://scanalyst.fourmilab.ch/t/the-birth-of-electronics-from-the-incandescent-lamp-to-digital-logic/3175 "2023-06-04T00:24:16Z")
The first digital logic gate built from vacuum tubes appears to have been invented by Bruno Rossi in 1930. Rossi, an Italian physicist studying cosmic rays and radioactivity, was not working on computing e… --- ## [RCA BIZMAC Computer](https://scanalyst.fourmilab.ch/t/rca-bizmac-computer/3047)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [15 April 2023 15:38 UTC](https://scanalyst.fourmilab.ch/t/rca-bizmac-computer/3047 "2023-04-15T15:38:02Z")
The Radio Corporation of America (RCA) BIZMAC computer was developed under a US$ 4.5 million contract from the U.S. Department of Defense Military Assistance Program awarded in 1951 to provide logistic supp… --- ## [Vacuum Tube Computer Part 30: Two Bytes of Memory](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-30-two-bytes-of-memory/2587)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [10 January 2023 12:53 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-30-two-bytes-of-memory/2587 "2023-01-10T12:53:51Z")
So far, the vacuum tube computer has consisted only of the central processor: arithmetic and logic unit, instruction decoder, and control logic. Now it’s time to give it some memory—a whole two bytes of it… --- ## [Building a 1920s Style Tube Amplifier—Starting with the Tubes!](https://scanalyst.fourmilab.ch/t/building-a-1920s-style-tube-amplifier-starting-with-the-tubes/2219)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [29 October 2022 16:31 UTC](https://scanalyst.fourmilab.ch/t/building-a-1920s-style-tube-amplifier-starting-with-the-tubes/2219 "2022-10-29T16:31:50Z")
Even in the golden age of do-it-yourself electronics, few hobbyists made their own vacuum tubes. Let’s see what it’ll take. --- ## [Vacuum Tube Computer Part 29: Address Line Buffers and Inverters](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-29-address-line-buffers-and-inverters/2127)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [10 October 2022 16:27 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-29-address-line-buffers-and-inverters/2127 "2022-10-10T16:27:27Z")
In order to select the desired cell in the computer’s memory array, the six address lines from the processor and their logical negations must be connected to the inputs of the memory decoder array, which re… --- ## [J. Presper Eckert Remembers the ENIAC](https://scanalyst.fourmilab.ch/t/j-presper-eckert-remembers-the-eniac/1959)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 4\ **Last updated:** [7 September 2022 14:47 UTC](https://scanalyst.fourmilab.ch/t/j-presper-eckert-remembers-the-eniac/1959 "2022-09-07T14:47:22Z")
J. Presper Eckert was, with John Mauchly, co-inventor of ENIAC, the first general purpose electronic computer. In this interview he discusses the machine and its design and shows one of the decimal ring cou… --- ## [Hewlett-Packard 711A Tube Power Supply Restoration](https://scanalyst.fourmilab.ch/t/hewlett-packard-711a-tube-power-supply-restoration/1784)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [2 August 2022 11:46 UTC](https://scanalyst.fourmilab.ch/t/hewlett-packard-711a-tube-power-supply-restoration/1784 "2022-08-02T11:46:10Z")
In the vacuum tube era, an engineer’s bench would often include a power supply able to provide the hefty voltages those devices required. The Hewlett-Packard 711A \[PDF\], introduced in 1954, was a particula… --- ## [Vacuum Tube Computer Part 28: An Emulator for the Hardware!](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-28-an-emulator-for-the-hardware/1610)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [28 June 2022 12:03 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-28-an-emulator-for-the-hardware/1610 "2022-06-28T12:03:44Z")
Any general purpose computer can emulate any other, constrained only by speed and memory constraints, and thus it’s possible to emulate the one-bit vacuum tube computer on a modern machine. Enthusiast “Ren… --- ## [Vacuum Tube Computer Part 27: Mounting the Monster](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-27-mounting-the-monster/1573)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 1\ **Last updated:** [21 June 2022 13:52 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-27-mounting-the-monster/1573 "2022-06-21T13:52:43Z")
Each board of the under-construction vacuum tube computer is 70×100 centimetres, and the full computer, including the now-complete processor, storage, program control, and input/output will add up to six bo… --- ## [Vacuum Tube Computer Part 26: Four Bits of Memory](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-26-four-bits-of-memory/1414)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 1\ **Last updated:** [23 May 2022 14:07 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-26-four-bits-of-memory/1414 "2022-05-23T14:07:59Z")
After designing the read/write memory cell in part 24, it’s time to start fabricating the first element of the random access memory array: four bits of individually addressable vacuum tube memory. The add… --- ## [Vacuum Tube Computer Part 25: Upgrading the Blinking Lights](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-25-upgrading-the-blinking-lights/1273)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [27 April 2022 13:32 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-25-upgrading-the-blinking-lights/1273 "2022-04-27T13:32:21Z")
The processor of the vacuum tube computer uses vacuum fluorescent displays (VFDs) to show the internal state of the machine. The method used to drive them was sensitive to the fan-out of the signal display… --- ## [Restoring a Hewlett-Packard 521A Frequency Counter, Part 2](https://scanalyst.fourmilab.ch/t/restoring-a-hewlett-packard-521a-frequency-counter-part-2/1120)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [30 March 2022 12:24 UTC](https://scanalyst.fourmilab.ch/t/restoring-a-hewlett-packard-521a-frequency-counter-part-2/1120 "2022-03-30T12:24:35Z")
Replacing aged capacitors and cleaning contacts brings the device to life—kind of—but it still isn’t remotely accurate. Tracking down the cause requires digging deeper into the circuitry. --- ## [Vacuum Tube Computer Part 24: Designing the Memory Element](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-24-designing-the-memory-element/995)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [8 March 2022 13:06 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-24-designing-the-memory-element/995 "2022-03-08T13:06:26Z")
After exploring a variety of alternatives, a vacuum tube flip-flop structure is chosen as the fundamental memory cell for the vacuum tube computer. This is a set-reset cell storing one bit of memory in two… --- ## [Restoring a Hewlett-Packard 521A Frequency Counter](https://scanalyst.fourmilab.ch/t/restoring-a-hewlett-packard-521a-frequency-counter/955)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [1 March 2022 16:07 UTC](https://scanalyst.fourmilab.ch/t/restoring-a-hewlett-packard-521a-frequency-counter/955 "2022-03-01T16:07:52Z")
Understandinging how the decimal counter modules work is worth the time to watch this video. I always assumed they were decimal ring counters, as used in ENIAC. But nooo—that would be too obvious for H-P … --- ## [Vacuum Tube Computer Part 23: Evaluating Memory Options](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-23-evaluating-memory-options/921)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [22 February 2022 12:51 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-23-evaluating-memory-options/921 "2022-02-22T12:51:14Z")
After completing construction and testing of the processor in Part 22, it’s time to move on to the next major subsystem of the computer: its memory. While it would be easy to interface a modern solid state… --- ## [Hewlett-Packard 521DR Digital Counter from the 1950s](https://scanalyst.fourmilab.ch/t/hewlett-packard-521dr-digital-counter-from-the-1950s/776)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [23 January 2022 14:45 UTC](https://scanalyst.fourmilab.ch/t/hewlett-packard-521dr-digital-counter-from-the-1950s/776 "2022-01-23T14:45:07Z")
Counting events or precisely measuring frequency with a digital readout may seem pretty simple, but in the 1950s doing it took a lot of vacuum tubes—so many that this vintage Hewlett-Packard laboratory inst… --- ## [Vacuum Tube Computer Part 22: CPU Complete!](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-22-cpu-complete/605)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [21 December 2021 13:36 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-22-cpu-complete/605 "2021-12-21T13:36:07Z")
As 2021 comes to a close, so does the first phase of the vacuum tube computer project with completion of the central processor unit (CPU). Although the computer still lacks memory and input-output faciliti… --- ## [Vacuum Tube Computer Part 21: Bits and Pieces](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-21-bits-and-pieces/569)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [14 December 2021 12:23 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-21-bits-and-pieces/569 "2021-12-14T12:23:35Z")
The core of the one-bit vacuum tube computer is almost complete. In this episode, the output multiplexer, skip-if-zero logic, and flag bit used to implement skip are added. In the process, some debugging … --- ## [Vacuum Tube Computer Part 20: Conditional Execution Logic](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-20-conditional-execution-logic/488)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [1 December 2021 16:11 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-20-conditional-execution-logic/488 "2021-12-01T16:11:00Z")
Much of the power of digital computers stems from their ability to make decisions and alter processing based upon the data they are manipulating. In high level languages, this is often expressed as if—then… --- ## [Vacuum Tube Computer Part 19: Two Phase Clock Buffer](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-19-two-phase-clock-buffer/385)
**Author:** [@johnwalker](https://scanalyst.fourmilab.ch/u/johnwalker)\ **Replies:** 0\ **Last updated:** [16 November 2021 14:48 UTC](https://scanalyst.fourmilab.ch/t/vacuum-tube-computer-part-19-two-phase-clock-buffer/385 "2021-11-16T14:48:35Z")
Many of the components of the one-bit computer require a clock signal, so the clock must drive a large number of inputs and requires buffering to provide the required current. In addition, because the inst… [Next page](https://scanalyst.fourmilab.ch/tag/vacuum-tube/300.md?match_all_tags=true&page=1&tags%5B%5D=vacuum-tube)