The Era of the Triode Radio 1920-1928

1. By Bob Voss, N4CD The Era of the Triode Radio1920-1928

2. 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!

3. Paragon 'Tuner” - 1920

4. Paragon Tuner Insides

5. Paragon Detector & Amp

6. Detector Amp Insides

7. Grebe TRF MU-1 Syncrophase

8. 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

9. 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

10. 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'

11. 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

12. 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

13. 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!)

14. 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

15. 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

16. Tubular Audions

17. Spherical Audion - 1908

18. 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

20. 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

21. 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

22. 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

23. DeForest Crystal Radio 1918

24. Variometer – variable “L”

25. 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”

26. The Diode Tube

27. The Triode Tube

28. Modern Triode Tube

29. “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

30. The Grid Leak Circuit

31. 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

32. Effect of Regeneration

33. The Regen Detector

34. “Tickler” Winding on Coil

35. 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

36. 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

37. The Early Commercial Regens • Crosley 2 tube (regen det and amp) 1923 era

38. RCA Radiola Regen Receiver

39. Radiola III insides

40. Radiola III insides

41. 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. $$$$

42. 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'

43. Triode 'stray' capacity

44. 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

45. 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

46. TRF circuit

47. Neutralization

48. 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

50. The Early “Speaker” - (milliwatts)