The Era of the Triode Radio
1920-1928
By Bob Voss, N4CD
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
Paragon Detector & Amp
Detector Amp Insides
Grebe TRF MU-1 Syncrophase
In 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




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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
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Silicon Crystal
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Galena Crystal
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Rare – 'tube detector' (mid 1910s)
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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 Audions
Spherical Audion - 1908
World War One
1914-1918

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
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1920 – First AM broadcast experiments
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1922 – First regular scheduled broadcasts
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Start of the 'mass produced radio'
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Hundreds of small (25-100w) stations
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Tubes quickly capable of thousands of watts of
power
People hungry for home entertainment
Early Receiver Design
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Pre 1922 or so – both military/home
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Used variable or tapped inductors for tuning
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Variometers – Variocouplers
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Good varible capacitors – 'not invented yet'

Used 'diode detectors' or 'grid leak detector'

Resistors - expensive/unreliable

If tube detector – battery powered
DeForest Crystal Radio 1918
Variometer – variable “L”
The First Common Triode Tube

Has a Filament, a 'grid' and a plate
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First commercial tubes – UV200 and UV201
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UV 200 – 'soft vacuum' detector
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UV 201 – 'hard vacuum' 'amplifier'
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Gain – maybe 8 to 10

Filament – 5V at 1 amp!
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Ran off battery power (wet cell “A”, dry cell “B”
The Diode Tube
The Triode Tube
Modern Triode Tube
“Grid Leak” Circuit


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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 Circuit
The Regen Receiver

Armstrong credited with 'inventing' the
regenerative receiver

Gain of hundreds of times (300-400 typical)
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Is a “Q Multiplier” for selectivity

1 Tube or 2 tubes – headphones
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3 tubes will drive horn speaker
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Needs good external antenna/ground

Hard to use for unsophisticated user
Effect of Regeneration
The Regen Detector
“Tickler” Winding on Coil
The Regen for Hams

Copies CW and AM
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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 insides
Radiola III insides
Mass 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

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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
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It's 'the only game in town'
Triode 'stray' capacity
The TRF – Tuned Radio Freq RX

Multiple Stages of Tuned RF Amps
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Followed by Grid Leak Detector

Avoids the Armstrong Patent on regen
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Multiple low gain stages (x10 each)
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Followed by one or more audio amp stages
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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 circuit
Neutralization
Taming the TRF


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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 Coils
Grebe – Coil Design – Gang Tuning
Binocular Coils
Reflex Receivers – Save a Tube
Reflexed Circuit
Fada Neutrodyne
Improvements

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!
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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