The Era of the Triode Radio 1920-1928

The Era of the Triode Radio1920-1928

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

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 Audions

Spherical Audion - 1908

World 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 1918

Variometer – 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 Tube

The Triode Tube

Modern 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 Circuit

The 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 Regeneration

The Regen Detector

“Tickler” Winding on Coil

The 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 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 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 circuit

Neutralization

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 Coils

Grebe – Coil Design – Gang TuningBinocular 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! 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