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YOU CAN BUILD AN OSCILLOSCOPE AROUND A REAL GLOWING TUBE

An electron beam draws waveforms live on a glowing phosphor screen—no ADC, no memory, just physics.

by Joshua Coleman

FULL CAD BOM FIRMWARE DOCS

WorkshopScience

difficulty
●●●●●
time
several weekends
license
license not specified
repo
repo ACTIVE7 stars

WHAT YOU’LL NEED

Videos
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COMPAREE VERDICT

This is a fully discrete, high-voltage oscilloscope built around a 2AP1A cathode-ray tube with a roughly 2 inch green phosphor screen. There is no analog-to-digital converter, no memory and no triggering system: the display is a real-time physical trace of voltage drawn by an electron beam. Deflection amplifiers output about 150–200 Vpp to the tube's electrostatic plates, and the high voltage supply delivers about 700–800 V DC at about 1 mA. In X-Y mode it draws Lissajous figures — feed it 1000 Hz and 999 Hz and the pattern slowly rotates, drifting at the 1 Hz difference. Coleman based the design on E. Tuttle's work from the University of Denver, now only on the Wayback Machine; a copy of that page is in the repo. This is a learning project, not a practical instrument. The README says so directly: it is about how electrons behave in electric fields, how analog systems represent signals and how early instrumentation worked. The repo gives you EAGLE schematics and boards and a clear architecture overview, but no bill of materials and no step-by-step assembly. You also have to find a 2AP1A tube yourself; the README does not say where. The real barrier is safety. The supply runs at about 700–800 V DC, the README warns of 700–1000 V in the circuit, and capacitors hold their charge after power-off — this voltage can kill. If you have never worked safely with high voltage, this is the wrong first project. If you have, it shows electron-beam physics with your own eyes in a way no simulation does.

GOOD TO KNOW

  • —EAGLE schematics and board files for the CRT control board and the deflection amplifier, plus a schematic for the power supply, are in the repository.
  • —No bill of materials. The README describes the architecture and principles but does not list part numbers or suppliers.
  • —No licence is stated in the repository.
  • —The original University of Denver design by E. Tuttle is archived on the Wayback Machine; Coleman saved a copy of the full page in the repo.
  • —The README does not say where to source the 2AP1A tube.
  • —The high voltage supply runs at about 700–800 V DC, and the README warns that 700–1000 V DC is present. This is lethal during operation, and capacitors stay charged after power-off.

Parts to buy

3 items

From our check of the build. Exact quantities and part numbers are in the creator’s BOM.

  • 2AP1A cathode-ray tubeFind
  • Components for the deflection amplifiersfrom the repo files
  • PCBs made from the EAGLE board filesfrom the repo files

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Can I build this?

PrintNothing required — this is a PCB and tube assembly.
Buy2AP1A cathode-ray tube (the README does not say where to get one), components for the deflection amplifiers, CRT control board and high voltage supply (no BOM provided — take values from the schematics), PCBs made from the EAGLE board files
ToolsPCB fabrication service or etching setup, soldering iron, high-voltage-rated meter and probes, mounting for the CRT, two signal sources for X-Y mode
SkillsHigh voltage electronics experience, analog circuit assembly, reading schematics and choosing parts without a BOM. Not a beginner project.
TimeSeveral weekends by our estimate. The README gives no build time.
Cost$$$ — the README gives no costs; the tube, the PCBs and the high-voltage-rated parts are all on you.
SafetyLethal high voltage. The supply runs at about 700–800 V DC, the README warns that 700–1000 V DC is present, and capacitors retain charge after power-off. Use the one-hand rule when probing, verify discharge before handling, use properly rated components and never modify wiring while powered. Handle the glass tube with care. If you have never worked safely with high voltage, do not start here.

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

Videos

Building a Cathode Ray Tube Oscilloscope6:28

Joshua Coleman's build video (26 Mar 2026), linked in the README.

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Gallery

Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Read the archived E. Tuttle design (Coleman's design is based on this page. A copy is also in the repo under 'Project Reference Webpage Complete'.)
  2. 2.Read the README (Architecture, CRT operation, Lissajous mode and the safety rules.)
  3. 3.Review the EAGLE files (CRT control board and deflection amplifier (schematic and board), power supply (schematic only). No bill of materials, so take part values from the schematics.)
  4. 4.Source a 2AP1A cathode-ray tube(The README does not say where to get one.)
  5. 5.Build and test the high voltage section with the README's safety rules(Lethal voltage: about 700–800 V DC from the supply, and the README warns of 700–1000 V in the circuit. Use the one-hand rule, verify discharge before handling, use properly rated components and never modify wiring while powered.)

Resources

Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.

KNOWN ISSUES

  • You have to source a 2AP1A cathode-ray tube yourself. The README does not say where to get one.
  • No bill of materials. You have to read component values from the EAGLE schematics and choose parts yourself.
  • High voltage capacitors hold charge after power-off. Verify discharge before you touch anything and never modify wiring while powered.
  • The README says the build is based on the Tuttle design and derived from classic ARRL-era circuits, using modern components where practical, but it does not list exactly what was changed. Do not assume the archived page matches Coleman's boards.
  • There are no instructions for adjusting focus and intensity. Those voltages come from a resistive divider on a 700–800 V network, so any adjustment means working near lethal voltage — use the one-hand rule.
  • Lissajous mode needs two signal sources for the X and Y inputs, for example 1000 Hz and 999 Hz as in the README.

Can I use a different CRT?

The repository is built around the 2AP1A, and the schematics and voltages are for that tube. Using another tube would mean redesigning the circuits yourself; the README does not cover it.

Is there a triggering circuit?

No. The README lists no ADCs, no memory and no triggering system, and basic waveform display has no timebase. The trace is a real-time physical representation of voltage.

What can I actually measure with this?

The README frames it as a learning instrument, not about performance: basic waveform visualization, X-Y plotting, comparing frequencies with Lissajous figures, and beam focusing and intensity control.

What does the screen look like?

The 2AP1A has a roughly 2 inch screen with P1 green, medium-persistence phosphor. The trace is drawn directly by the electron beam.

How dangerous is it?

Very. The high voltage supply runs at about 700–800 V DC, the README warns that 700–1000 V DC is present, and capacitors keep their charge after power-off. Its safety rules: use the one-hand rule when probing, verify discharge before handling, use properly rated components and never modify wiring while powered.

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Discussion1

FROM THE COMPAREE TEAM

Coleman's design runs the 2AP1A from a supply of about 700–800 V, with deflection amplifiers swinging 150–200 Vpp. What signal would you feed it first to see the trace?

CompareeTEAM1d ago

Checked against the repository and README: there are EAGLE schematics and boards for the CRT control board and deflection amplifier, a schematic for the power supply, and a saved copy of the original Tuttle design — but no bill of materials, no assembly guide and no licence. The README is clear about the danger: the supply runs at about 700–800 V DC, it warns that 700–1000 V is present, and capacitors hold charge after power-off, but it does not walk you through a discharge or bring-up procedure. If you have never built a high-voltage analog circuit, do not start here. If you have, and you want to see electron-beam physics with your own eyes, the repository gives you enough to start.

Joshua Coleman

Joshua Coleman (Joshua Coleman Makes) built this CRT oscilloscope to understand how electrons behave in electric fields and how early instruments worked. He based it on a design by E. Tuttle (University of Denver), now only on the Wayback Machine, and saved a copy of that page in the repository.

GitHub

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  • Comparee is not the author of the projects featured here. All rights to each project belong to its creator — every page links to the original source, and we never host creators’ files.
  • Information is provided without warranty and may become outdated as projects evolve. Prices are indicative bands only — always check the creator’s parts list for current costs.
  • Building and operating any project is at your own responsibility. Protective equipment, safe workshop practice and compliance with local regulations are the builder’s responsibility.
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