Above:

American Shure advert from 1943 for their 'fighting microphones' . WWII caused makers in both UK and USA to divert production to the military. This type of patriotic advert was typical of the era.

Above:

 a mirror-screw mechanical scanning device designed for high definition (i.e. >120 lines). This particular one was made by a German firm. The long edge of each strip has a highly reflective mirror finish. A modulated light spot would be reflected from each mirror which, as it rotated, would cause a strip of light of varying intensity to pass across the rear of a ground glass screen, equivalent to a single line scan for each mirror. The number of mirrors therefore determined the maximum number of lines in the final picture. The picture size would be approximately equal in height to the vertical dimension of the mirror screw. The field scanning rate would be determined by the RPM of the driving motor, itself controlled by magnetic braking provided by synchronizing pulses fed into coils acting on the toothed wheel near the bottom.

These devices, being mechanical, demanded a degree of accuracy in construction that was, in practice, barely achievable: the problem that dogged all mechanical TV systems.

QUIZ #1 ANSWERS

1. British Broadcasting Company
2. Nipper
3. Permanent Magnet, Mains Energised. On the latter, the field coil generates the required magnetic field and usually doubles as a smoothing choke
4. Wells Coates (architect) 
5. Amplitude Modulation: The 'height' of the waveform is modulated by the sound. Frequency Modulation: the width of the 'sweep' across a band of frequencies centred on the carrier frequency is modulated by the sound.
6. John Logie Baird
7. John Logie Baird!
8. John Logie Baird's ventriloquist's dummy, used as a subject to be televised during his long hours of experimenting
9. Paul Nipkow
10. On capacitors (condensers) in RF stages in radios
11. Beam tetrode

12. He invented the triode valve

13. America

14. AC/DC, universal. Also acceptable: AC mains/battery types, as these usually have the valve filaments wired in series to make current/voltage provision easier to achieve
15. It is the insulating medium in a capacitor, between the plates

16. Philips

17. Bakelite
18. An octal valve has eight pins arranged in a circle, with a central locating spigot
19. Tuned Radio Frequency
20. Urea Formaldehyde

 Quiz #2 ANSWERS

1. A filament is found in directly heated (i.e. battery) valves and is the source of free electrons for the operation of the valve. A heater is found in indirectly heated (i.e. A.C. mains) valves. Its purpose is to heat the cathode to a temperature at which it will emit free electrons. (The 'warm-up' time)
2. The Barretter is a device designed to function rather like a superior ballast resistor. It maintains a constant current through any circuit to which it is connected despite variations in voltage.
3. AC/DC sets have valve heaters wired in series. One open-circuit heater and the set is 'dead'. Therefore the most likely problem with the faulty valve is an 'open' heater.
4. Ripple current is the measure of any remaining A.C. in the output of a rectifier/smoothing circuit. Ripple is caused by the regular charging and discharging of the reservoir capacitor. Even though capacitors may be rated at RMS ripple values, ripple is of a sawtooth form, rather than a sine wave. A full-wave rectifier system will result in a 100 Hz ripple: a half-wave system in a 50 Hz ripple. The reservoir capacitor should be rated well in excess of any likely ripple current level.
5. Colour codes are used on resistors and on smaller (PF, NF) capacitor values.
6. A.F. Audio Frequency - pitched within the range of human hearing.
7. The term 'audio' law means that the potentiometer is designed to work logarithmically (log law, in fact). This log scale matches the response of human hearing. Linear law potentiometers are not suitable (usually) for volume control purposes as they seem to be 'one-ended' with all the changes taking place at one end or other of the control. They are useful for other functions such as tone control.
8. Vari-mu valves were used for volume control, the control varying the voltage on the grid and, therefore, the gain.
9. Interlacing is a method of doubling the apparent scanning frequency of a TV tube by interleaving the raster lines. 25 full frames per second but scanned at 50 times a second (50 Hz) at only half the lines, the second half set completing the full raster. It is said to limit the inevitable flicker.
10. Beam-forming plates focus the electron stream onto the anode in a power tetrode valve.
11. 'Tygan' is a woven fabric of man-made fibres, often used as a cabinet covering material for portables and, sometimes, as loudspeaker grille cloth.
12. The frame aerial was used for most valve portable radios.
13. B.A. =British Association.
14. Frank.
15. A 'tweeter' is a miniature sound reproducer intended to bring out the highest audio frequencies. As AM radios are limited to 8Khz or less, tweeters are not very effective!
16. Capacitors.
17. The mains, via voltage selection devices, switch and, sometimes, a fuse.
18.  'DDT' = double diode triode
19. Put simply, impedance is the sum of resistance and reactance. It should not be confused with resistance: measure the impedance of an 8 ohm speaker and you will measure less than any 8. The symbol is Z. There is more to this, of course, but this is not the place for it.
20. The reaction control was found in many TRF sets of the early 1930s.Sometimes called regeneration, it fed the signal from a valve anode back to the grid to be amplified again. This made the control rather sensitive in use and affected by the frequency of the received transmission, but it gave a terrific boost in reception - until the set burst into oscillation. Do not confuse with reactance.

Quiz #3 ANSWERS

1. The well-known pipe-smoking gent who's name was also the brand name of his radio firm was Frank Murphy (Murphy radio ads of the 'thirties)

2. Ferrite is the iron-dust compound used to make coil cores and aerial rods.
3. Interlacing is the process by which a CRT (picture tube) face is scanned. As a simplified example, with the 625 line system, 312.5 lines are scanned, then the next 312.5 are scanned between the first set.
4. Part of the electron gun, a bent-gun ion trap can be found in a monochrome cathode-ray tube of the 1950s period.
5. 'VHF/FM' stands for Very High Frequency/Frequency Modulation.
6. The initials 'PAL' are short for Phase Alternating Line
7. Outdated 'LF' = AF (audio frequency)
8. The mirror-screw  was an early TV scanning device intended to supplant the Nipkow disc
9. An indirectly heated rectifier in an AC mains set is considered preferable to a directly heated one because the slow warm up means gradual HT potential rise.
10. there are four elements. Anode, Grid, Cathode, Heater. 
11. SW (short wave, but referring to medium wave when used)
12. They provided replacement dial cards

13. The term 'pot' is short for Potentiometer

14. Two commercial radio stations popular in the late thirties/early forties  were Radio Normandie, Radio Luxembourg

15. The terms 'B7G' and 'B9A' refer to miniature valve bases
16. Copper Oxide was used to make one of the types of rectifier of the air-cooled (finned) or contact-cooled variety

17. Philips (on TRF sets in the 'thirties)

18. A 'voice coil' or speech coil can be found in a moving coil loudspeaker
19. Frame aerials were commonly used in  portable radios of the 'thirties, 'forties or earlier 'fifties
20. Pick Up. To attach a magnetic or crystal pick-up from a gramophone in order to amplify recorded sound -play records!

Score (for each quiz) 18 or more - you know your stuff - but get out more...

Score 15-17 - good going. Well done

Score 10-14 - not a bad try

Less than 10 - commiserations...