Electronics: amplification and switching
Control a large current with a small one.
Everything for this step
- Field guide
- The electromagnetic spectrum → 2 sections Physics → 12 sections Computer science → 6 sections Electronics and computer hardware → 19 sections
- Builds
- None yet.
- Reference sheets
- 1 sheet in The electromagnetic spectrum
- Sciences it rests on
- Physics
- Track
- Electronics and computing, level 1 of 1 · next: Semiconductors
Why this matters
Amplification is the primitive operation of the entire information age. Once you can make a small signal control a large one, you can build amplifiers, oscillators, logic gates and memory — and everything above this step is a rearrangement of those four.
The shape of it
- Vacuum tubes are the achievable path. A heated cathode, a control grid and an anode in an evacuated envelope. This is workshop-scale technology: it needs glassblowing, a vacuum pump and patience — not a clean room.
- Get the vacuum right. Tube life and performance are almost entirely a vacuum-quality problem. You need a good pump and a getter — a reactive metal flashed inside the envelope to absorb residual gas after sealing.
- Make good passive components first. Stable resistors and capacitors, and reliable insulation. Circuits fail at their passives far more often than at their active devices, and this is where your polymers earn their place.
- Build test equipment before circuits. A meter, a signal generator and above all an oscilloscope. Debugging electronics without an oscilloscope is guessing — and the oscilloscope is itself just a tube, so it is within reach.
- Then build the useful things: radio transmitters and receivers, public address, telephone exchanges, instrumentation, and control systems for your industrial processes.
- Then logic. A tube can switch as well as amplify, and switches in the right arrangement compute. A vacuum-tube computer is genuinely achievable for a small industrial society — large, hot, power-hungry and slow, but real, and it will do arithmetic no human team can match.
- Recognise the ceiling honestly. Tube electronics will take you to roughly 1945. Everything past that requires the semiconductor step, and the semiconductor step requires an industrial base you may not have.
Doing it, step by step
The summary above says what has to happen. This says how, with the numbers that decide whether it works.
1 · Build the vacuum system and learn to read it
Tube life and performance are almost entirely a vacuum-quality problem. Use two pumps in series: a mechanical rotary pump to take the envelope down to roughly 1 pascal, then a diffusion pump — oil vapour jets that sweep gas molecules out — to reach around 10⁻⁴ pascal.
Bake the envelope at a few hundred degrees while pumping to drive gas out of the glass and metal. Read the vacuum with a high-voltage spark coil touched to the glass: a pink or purple glow means air remains; as vacuum improves the glow fades and disappears.
2 · Build the tube, seal it, and flash the getter
Inside the envelope: a cathode — a nickel sleeve coated with barium and strontium oxides, heated indirectly to roughly 800 °C — a grid of fine wire wound around it, and an anode plate outside that. Bring the leads out through glass-to-metal seals using a wire that expands at the same rate as the glass.
After sealing off, heat the getter — a small reactive barium charge — to flash it onto the inside of the glass, where it absorbs remaining gas. A silvery getter mirror that turns milky white means air has leaked in — the tube is dead.
3 · Treat high voltage and glass envelopes as dangerous
Tube equipment runs at hundreds of volts, and capacitors hold that charge after power is off. A cathode-ray tube can run at many thousands of volts.
- Discharge filter capacitors with an insulated shorting stick before touching a circuit.
- Keep one hand away from the chassis when probing live circuits.
- Interlock covers on power supplies.
- Evacuated glass implodes, throwing glass: eye protection whenever tubes, and especially large cathode-ray tubes, are handled or worked on.
4 · Make reliable passive components and measure them
Circuits fail at their passives far more often than at their active devices. Make carbon-composition and wire-wound resistors, mica and paper-in-oil capacitors, and transformers and chokes with good insulation — where polymers earn their place.
Measure every value with a Wheatstone bridge against a reference standard, mark each component with its value and tolerance, and test a sample at working temperature — values drift when warm. Reject anything outside tolerance.
5 · Build a regulated power supply before any circuit
Unstable power supplies make every fault intermittent and unfindable. A supply is: a transformer, a rectifier — a tube rectifier — a filter of capacitors and a choke to smooth the ripple, and a regulator to hold the voltage steady as load changes.
Measure the ripple and the voltage change from no load to full load, and write both on the supply. Fuse the input and the output.
6 · Build test equipment before circuits
Debugging electronics without an oscilloscope is guessing. In order:
- A meter — a moving-coil galvanometer with shunts for current and series resistors for voltage, calibrated against standards — see instruments.
- A signal generator — a tube oscillator with a calibrated dial.
- An oscilloscope — a cathode-ray tube with deflection plates driven by an amplifier, and a timebase that sweeps the beam across the screen. It is itself just tubes, so it is within reach.
7 · Build amplifiers, then logic — and state the ceiling
Build the useful things: radio receivers and transmitters — see radio — telephone amplifiers, instrumentation and industrial controls. Then logic: a tube switches as well as amplifies, and two tubes cross-coupled make a flip-flop that stores one bit. That is enough to build a computer.
Recognise the ceiling honestly. Tubes are hot, power-hungry, and fail after thousands of hours. Tube electronics will take you to roughly 1945. Everything past that requires semiconductors, and the jump is not incremental.