The Era of the Triode Radio 1920-1928

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By Bob Voss, N4CD. The Era of the Triode Radio 1920-1928. The Beginnings of “Tube Radio”. In the beginning The invention of the Tube The regenerative radio The TRF receiver The TRF era Beyond the “triode” PATENTS! Marconi!. Paragon 'Tuner” - 1920. Paragon Tuner Insides.
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By Bob Voss, N4CDThe Era of the Triode Radio1920-1928The Beginnings of “Tube Radio”
  • In the beginning
  • The invention of the Tube
  • The regenerative radio
  • The TRF receiver
  • The TRF era
  • Beyond the “triode”
  • PATENTS! Marconi!
  • Paragon 'Tuner” - 1920 Paragon Tuner InsidesParagon Detector & AmpDetector Amp InsidesGrebe TRF MU-1 SyncrophaseIn the Beginning
  • Up to 1895 - There was 'Static' – but no one listened to anything
  • Marconi invents 'Spark Gap' radio -more static
  • Marconi and others invent 'spark gap' receivers
  • The world is full of profitable 'useful noise'
  • Soon 'chaos' fills the airwaves – loud wins
  • Primitive technology – that 'works'
  • Marconi owns radio technology through patents
  • What is a 'receiver'?
  • Converts RF signals (power) into something that can be heard, seen, or copied – (audio)
  • Ideally has good 'selectivity' to choose the signals you want from the ones you don't
  • Is 'affordable' and 'reliable'
  • Has good sensitivity to hear 'weaker signals'
  • Can be used 'anywhere' easily
  • Easy to use
  • Power - It's all about power
  • Signals are in microvolts – 1 uV is less than picowatt of power into 1K long wire
  • Big antenna to collect lots of 'RF' power
  • Human can hear fractions of a microwatt with good headphones (crystal radio for example)
  • Best 'horn speakers' need fractions of a milliwatt
  • Receivers provide the 'power gain'
  • Ham Radio History
  • 1910s – Experimenters –
  • 1914 – Hams banished to 'below 200 meters'
  • Hams given 'useless frequencies'
  • This is the era of 'spark and arc'
  • Commercial – Rotary Spark and Poulson Arc
  • Most using non-tube receivers
  • Hams off the air in US - 1917 to 1918 – WW I
  • Commercial Radio
  • 0.5 to 250K Poulson Arc
  • Thought Lower Frequencies better
  • Marconi – 250M and 500M standard freqs
  • Transatlantic – 1000 to 3000 Meters
  • Marconi 'owned radio' through patents
  • Expensive 'tube' RX - rare
  • Early Receivers
  • Coherer – Brantley – glass tube/iron filings
  • Marconi Magnetic Detector (“Maggie”)
  • Liquid Baretter
  • Silicon Crystal
  • Galena Crystal
  • Rare – 'tube detector' (mid 1910s)
  • Headphones (sensitive! expensive!)
  • Early receivers
  • Needed multiple 'high Q' tuned circuits
  • Tried to 'match' antenna for max power capture
  • Detector loaded down tuned circuits
  • Marconi owned the patents on 'tuning'!
  • Tuning often determined by your antenna!
  • A good receiver covered 300-3000 meters
  • Needed 'good ears' and good headphones
  • The Tube – The Game Changer
  • 1904 – Fleming “Valve” - diode
  • 1906 – De Forest - “Audion” triode
  • Ma Bell mades 'long distance amplifer'
  • Hand made in light bulb factory
  • Unreliable, very expensive, fragile
  • Tubular AudionsSpherical Audion - 1908World War One1914-1918
  • Military Needs Communications – Pronto!
  • Ship to Shore / Ship to Ship / Ship intercom
  • US to Europe
  • Development of “Standard Tubes' VT1 VT2
  • 500,000 tubes made – mostly for audio!
  • Europe has the technology to do it – not US
  • World War I Aftermath
  • Large Tube Making Capacity – military winds down after war
  • Marconi patents 'confiscated' during war
  • The arrival of the 'gang of 4' who owned patents
  • Hams back on the air
  • Sarnoff arrives – RCA
  • Home entertainment schemes – tel wires
  • AM Broadcasting Era starts
  • 1920 – First AM broadcast experiments
  • 1922 – First regular scheduled broadcasts
  • Start of the 'mass produced radio'
  • Hundreds of small (25-100w) stations
  • Tubes quickly capable of thousands of watts of power
  • People hungry for home entertainment
  • Early Receiver Design
  • Pre 1922 or so – both military/home
  • Used variable or tapped inductors for tuning
  • Variometers – Variocouplers
  • Good varible capacitors – 'not invented yet'
  • Used 'diode detectors' or 'grid leak detector'
  • Resistors - expensive/unreliable
  • If tube detector – battery powered
  • DeForest Crystal Radio 1918Variometer – variable “L”The First Common Triode Tube
  • Has a Filament, a 'grid' and a plate
  • First commercial tubes – UV200 and UV201
  • UV 200 – 'soft vacuum' detector
  • UV 201 – 'hard vacuum' 'amplifier'
  • Gain – maybe 8 to 10
  • Filament – 5V at 1 amp!
  • Ran off battery power (wet cell “A”, dry cell “B”
  • The Diode TubeThe Triode TubeModern Triode Tube “Grid Leak” Circuit
  • Provides 'diode' detection – grid acts like a plate – fairly sensitive
  • Provides Audio Gain - maybe x10
  • Is high impedance input – no loading on tuned circuit
  • Is used in 'almost every' 1920s receiver!
  • Parts – tube, expensive resistor, 2 capacitors
  • The Grid Leak CircuitThe Regen Receiver
  • Armstrong credited with 'inventing' the regenerative receiver
  • Gain of hundreds of times (300-400 typical)
  • Is a “Q Multiplier” for selectivity
  • 1 Tube or 2 tubes – headphones
  • 3 tubes will drive horn speaker
  • Needs good external antenna/ground
  • Hard to use for unsophisticated user
  • Effect of RegenerationThe Regen Detector“Tickler” Winding on CoilThe Regen for Hams
  • Copies CW and AM
  • Spark outlawed in 1926 (gone by '24 really)
  • Provides 'two signal reception'
  • Sensitive – up to 10 MHz
  • Everything 'detunes' it – hand capacity, antenna in wind, voltage, strong nearby signals
  • Cheap! Easy to make
  • Works on those 'useless frequencies' > 1.5 Mhz
  • Regens for Broadcast
  • Tubes – 'expensive' – the fewer the better
  • Took big outside antennas – no one cared
  • Battery powered – only half of homes had A/C
  • BC radio was the latest 'gadget' that everyone had to have
  • Used only 1 or 2 expensive tubes
  • Started the 'mass production' of radios
  • The Early Commercial Regens
  • Crosley 2 tube (regen det and amp) 1923 era
  • RCA Radiola Regen Receiver Radiola III insidesRadiola III insidesMass Market Regen Problems
  • Dead spots – antenna length/impedance
  • Oscillator radiation -
  • Two hand operation and 'hunt and find' operation – need to track 'knob positions'
  • Strong signal capture
  • Audio is 'clipped' at high regen level
  • Requires constant adjusting of gain when changing freq
  • The 'gang of 4' owned the patents. $$$$
  • Triode Problems
  • Triodes love to oscillate – higher freqs even more so.
  • 1920 triodes have low gain
  • 1920 triodes have large internal parts
  • 1920 triodes require transformer coupling for maximum power transfer
  • 1920s circuits are built on wood chassis
  • It's 'the only game in town'
  • Triode 'stray' capacity The TRF – Tuned Radio Freq RX
  • Multiple Stages of Tuned RF Amps
  • Followed by Grid Leak Detector
  • Avoids the Armstrong Patent on regen
  • Multiple low gain stages (x10 each)
  • Followed by one or more audio amp stages
  • MAJOR problems with self oscillation
  • Used more power hungry tubes
  • Early TRF Receivers
  • Every stage had a tuning knob! (Var “C”)
  • All built on wood chassis
  • Fancy cabinets/layouts were called for
  • Didn't work at higher frequencies (>1.5 MHz)
  • Many were unstable and self oscillated
  • Easier to use than regen, but not much!
  • Still needed big outside antenna
  • Power hungry – typically 5 tubes
  • TRF circuitNeutralization Taming the TRF
  • Three Axis Coil layout (X,Y, Z)or 65 deg
  • Ganged Tuning - “Single Dial” (never worked all that well, but good enough for many)
  • AC to DC 'power packs' for “B” battery, then “A” battery
  • Invention of the “AC tube” (indirectly heated fil)
  • NEUTRALIZATION
  • The Early “Speaker” - (milliwatts)Erla Toroid CoilsGrebe – Coil Design – Gang TuningBinocular CoilsReflex Receivers – Save a TubeReflexed CircuitFada NeutrodyneImprovements
  • Shielding (late 20s)
  • AC 'tubes' – indirectly heated cathodes
  • Metal Chassis and Compartments
  • Screen Grid Tube (Tetrode) – 1927 on
  • AC Powered Radio - 1927 (PS Internal)
  • Superhet (1927 forward) – PATENTS!
  • Pentode and “Pentagrid” tubes (1929)
  • The “All American Five” design – 5 tubes
  • Multi-Section Tubes!
  • Triode Radio
  • Started with 'detector tube'
  • Battery powered radio – Regen and TRF
  • Neutrodyne Radio
  • Single Dial Radio (half success)
  • AC Powered Radio
  • Tetrodes and Pentodes
  • Shielding
  • Superhet takes over BC radio
  • The End
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