Chapter 14

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  • How old can radio technology be and still be used on the air today?
  • Why bother with vacuum tubes?

– Glowing filaments, colored plasmas, and Jules Verne glass envelopes

  • Power supplies for tubes

High voltage power supply safety

  • The old-tech QRP transmitter

Vacuum tube amplifiers
The three roles of the triode filament
RF sinewave oscillator
Quartz crystals
Triode and pentode oscillators

  • Old-tech voltage regulation – big, crude, expensive, but beautiful
  • The travails of triode tubes

The oscillator and buffer
The final amplifier – triodes chirp

  • The transmitter power supply

An inadequate supply from a 1935 radio
A good power supply made from cheap, modern, boring parts
How to check out junk power transformers
A complex but adequate supply made from ancient parts

  • It works! No one suspects it’s old and it’s a success on today’s 40 meter band
  • An old-tech receiver

A super regenerative receiver made from ancient tubes
The power supply
Super-regen on the modern hambands

Lots of fun, but not up to modern QRM & QRPs – back to the drawing board!