Radio & Telephone

Part of Phase 5: Rebuilding Technology

Radio & Telephone had two exact-duplicate label pairs — two articles both called “Electrode Assembly” and two both called “Vacuum Tubes” — fixed below. It otherwise runs from vacuum-tube theory through building one from scratch, amplifying and oscillating a signal, and finally radio and antenna work. Vacuum Tubes is the overview, explicitly requiring Radio and electrical theory first, and Radio itself requires only Telegraph and basic electrical circuits.

Vacuum Tubes, Thermionic Emission, Grid Control, The Diode, The Triode, The Tetrode, The Pentode, Multi-Grid Tubes, Beam Power Tube, Space Charge, and Amplification Factor cover tube theory. Thomas Edison first noticed electrons escaping a heated filament in 1883; Fleming’s 1904 diode and de Forest’s 1906 grid turned that into the triode, with typical amplification factors running 5-100. A tetrode’s screen grid drops plate-to-grid capacitance by a factor of 1,000 or more, and a pentode pushes gain control further still — the 6BA6, 6SK7, EL34, EL84, and KT88 all dominated radios from the 1930s through the 1960s.

Vacuum Tube Fabrication, Cathode Materials, Electrode Assembly: Cathode Filament, Electrode Assembly: Grid Spacing, Heater Design, Tube Fabrication, Envelope Construction, Glass Envelope Work, Gettering, Vacuum Pumping, and Diode Construction cover building one from scratch. Thoriated tungsten runs at 1,600-1,800°C and outlasts pure tungsten, which needs 2,200-2,500°C and barely survives a few hundred hours, and a control grid wound from 0.02-0.05 mm wire has to sit within 0.1 mm of its design spacing from the cathode or the tube runs hot or barely amplifies. The envelope itself needs its gas emptied to one hundred thousand times below atmospheric pressure, and skipping annealing cracks it weeks later — the fix is holding it at 500-560°C, then cooling no faster than 2 degrees a minute.

Amplifier Circuits, Common Cathode, Cathode Follower, Cascading Stages, Load Line Analysis, Operating Bias Point, Push-Pull Output, and Feedback Principle cover turning a tube into a working amplifier stage. A single triode stage gains a signal only 10-100 times, so reaching a speaker’s volts from a microphone’s millivolts means cascading several stages, and Harold Black’s 1927 negative feedback turned amplifier design from an art reliant on hand-matched tubes into an engineering discipline with stable gain.

Rectification, Half vs Full Wave, and Battery and Powering cover turning AC into the DC a tube actually runs on, typically 150-600 volts. Oscillator Circuits, Colpitts Oscillator, and Hartley Oscillator cover generating a signal in the first place — quartz crystal oscillators run Q values of 10,000-1,000,000 against 100-500 for a good LC circuit, and the Hartley (1915) and Colpitts (1918) designs both still build easily from salvage.

Radio, Crystal Radio, Cat’s Whisker, Receiver Construction, Regenerative Receiver, and Superheterodyne cover receiving a signal. A basic crystal radio with 60-80 turns on a cardboard tube reaches AM stations 50-100 km out with no power source at all, and a regenerative receiver’s feedback multiplies that gain, its tickler coil running only 5-15% as many turns as the main coil. Edwin Armstrong’s 1918 superheterodyne design had displaced every rival by the 1930s and still underlies AM, FM, and cell phones today.

AM Transmitter, Transmitter Construction, and Modulation Concepts cover sending one. A spark-gap transmitter needs only a charged capacitor across two small metal balls a few millimeters apart for Morse code bursts over tens of kilometers, and suppressing the carrier and one sideband lets SSB deliver about 9 dB more signal than AM for the same power.

Antenna Design, Dipole Antenna, Vertical Antenna, Loop Antenna, Frequency Selection, and Wave Propagation cover getting the signal into the air and across distance. A half-wave dipole’s length in meters is 142.5 divided by frequency in MHz, and the same 10-watt transmitter can reach thousands of kilometers on the right frequency or fail to cover 100 km on the wrong one — propagation, not power, decides it.

Impedance Matching is the one telephone-specific article here: telephone circuits settled on standard impedances, commonly 600 ohms, because a mismatch between source and load wastes power and causes line reflections.

Tube Theory

How a vacuum tube actually controls current, from the first diode to the multi-grid designs that followed.

Building a Tube from Scratch

Filament, grid, glass envelope, and vacuum — every physical step of hand-building one.

Amplifier Circuits

Turning one tube’s gain into a usable amplifier stage, stacked and stabilized.

Rectification and Power

Converting AC into the steady DC a tube circuit actually runs on.

Oscillators

Generating a signal in the first place, before anything amplifies or transmits it.

Radio Receivers

From a powerless crystal set to the superheterodyne design still used today.

Transmitters and Modulation

Sending a signal, and the modes that squeeze more range out of the same power.

Antennas and Propagation

Getting a signal into the air, and the physics that decides how far it actually travels.

Telephone Circuits

The one standard that keeps a telephone line from wasting its own power.

Impedance Matching

Explorer