MILLER Valve Radio and Audio Repair Handbook

1. Auflage 2000
ISBN: 978-0-08-052042-1
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 288 Seiten

Valve Radio and Audio Repair Handbook is not only an essential read for every professional working with antique radio and gramophone equipment, but also dealers, collectors and valve technology enthusiasts the world over. The emphasis is firmly on the practicalities of repairing and restoring, so technical content is kept to a minimum, and always explained in a way that can be followed by readers with no background in electronics. Those who have a good grounding in electronics, but wish to learn more about the practical aspects, will benefit from the emphasis given to hands-on repair work, covering mechanical as well as electrical aspects of servicing. Repair techniques are also illustrated throughout. This book is an expanded and updated version of Chas Miller's classic Practical Handbook of Valve Radio Repair. Full coverage of valve amplifiers will add to its appeal to all audio enthusiasts who appreciate the sound quality of valve equipment. - A practical manual for collectors, owners, dealers and service engineers - Essential information for all radio and audio enthusiasts - Valve technology is a hot topic

Zielgruppe

Academic/professional/technical: Research and professional

Autoren/Hrsg.

Miller, Chas

Inhaltsverzeichnis

1;Front Cover;1
2;Valve Radio and Audio Repair Handbook;4
3;Copyright Page;5
4;Table of Contents;6
5;Dedication
;3
6;Preface;6
7;Part 1:;12
7.1;Chapter 1. Basic facts you need to know about electricity and magnetism;14
7.1.1;Electricity from batteries;14
7.1.2;Electricity and magnetism;15
7.1.3;Induction and transformers;19
7.1.4;Practical transformers;20
7.1.5;Auto-transformers;20
7.1.6;Transformers and DC;21
7.1.7;To sum up;22
7.2;Chapter 2. What you need to know about voltage, current, resistance and Ohm's law;23
7.3;Chapter 3. What you need to know about real life resistors;27
7.3.1;Standard values;28
7.3.2;Resistors in series and parallel;28
7.3.3;Series/parallel resistors and wattage;29
7.3.4;What do resistors do in radio sets?;29
7.3.5;Variable resistors;30
7.4;Chapter 4. What you need to know about condensers;31
7.4.1;Electrolytic condensers;33
7.4.2;Leakage current and re-forming;34
7.4.3;Condensers and AC voltages;34
7.4.4;Variable condensers;34
7.4.5;Pre-set condensers;35
7.4.6;Yes, but what do condensers do?;35
7.5;Chapter 5. What you need to know about tuning;37
7.5.1;A use for the acceptor circuit;38
7.5.2;Frame aerials;38
7.5.3;Air cores and iron dust cores;39
7.5.4;Permeability tuning;39
7.5.5;Ferrite rods;39
7.6;Chapter 6. What you need to know about valves (1);40
7.6.1;Valve characteristics;41
7.7;Chapter 7. What you need to know about valves (2);44
7.7.1;The triode as oscillator;48
7.8;Chapter 8. What you need to know about the principles of transmission and reception;49
7.8.1;Sidebands;50
7.8.2;Receiver principles;51
7.9;Chapter 9. Practical receiver design (1): battery operated TRFs;54
7.9.1;Sharp cut-off versus variable mu;56
7.9.2;Extending the tuning range;56
7.9.3;Improving the output;59
7.9.4;Automatic Grid Bias;61
7.10;Chapter 10. Mains valves and power supplies;62
7.10.1;Cathode bias;62
7.10.2;Types of mains valves;62
7.10.3;Negative smoothing;64
7.10.4;'Swinging choke' smoothing;65
7.10.5;Directly or indirectly heated?;65
7.10.6;The voltage doubler;65
7.10.7;Isolated chassis;66
7.10.8;Different mains supplies;66
7.10.9;AC/DC receivers;67
7.10.10;Barretters;68
7.10.11;Rectifiers in AC/DC receivers;68
7.10.12;'Live' chassis;68
7.10.13;Part AC-only sets;68
7.10.14;Appendix;69
7.11;Chapter 11. What you need to know about the superhet;71
7.11.1;Keeping the local oscillator in step;72
7.11.2;Automatic volume control;74
7.11.3;An alternative delay method;75
7.11.4;The 'short' superhet;75
7.11.5;A good basis for study;75
7.11.6;Reflex amplifiers;76
7.11.7;Part superhets;76
7.11.8;Battery superhets;76
7.11.9;Appendix;77
7.12;Chapter 12. Some more special features found in superhets;82
7.12.1;Tuning indicators;82
7.12.2;Automatic tuning;83
7.12.3;Motor tuning;85
7.12.4;Automatic frequency control;86
7.12.5;Silence between stations;87
7.12.6;Amplified AVe;87
7.12.7;Push-pull output;89
7.12.8;Better tone control systems;90
7.12.9;Band-spread short wave tuning;91
7.12.10;The double superhet;91
7.12.11;'Television sound';91
7.13;Chapter 13. Battery and mains/battery portable receivers;92
7.13.1;'All-dry' portables;92
7.13.2;Miniature valves;93
7.14;Chapter 14. Automobile receivers;95
7.14.1;Negative or positive earthing;96
7.14.2;Constructional aspects;96
7.14.3;Permeability tuning;96
7.14.4;Some unusual sets and features;97
7.14.5;AM/FM automobile receivers;97
7.15;Chapter 15. Frequency modulation;98
7.15.1;Some aspects of FM receiver design;100
7.15.2;De-emphasis
;100
7.15.3;Design aspects of British FM receivers;100
8;Part 2:;102
8.1;Chapter 16. Tools for servicing radio receivers;104
8.1.1;Solder 'guns';104
8.1.2;Solder;104
8.1.3;What about instruments?;104
8.1.4;What ranges are required?;105
8.1.5;The ohms-per-volt game;105
8.1.6;What does ohms-per-volt mean inpractice?;105
8.1.7;The right way round for meters;106
8.1.8;The signal generator;106
8.1.9;The resistance and capacity bridge;107
8.1.10;What about an oscilloscope?;107
8.1.11;The output meter;107
8.1.12;Valve testers;107
8.1.13;The Mullard 'high speed' valve tester;108
8.2;Chapter 17. A few words about safety precautions;109
8.2.1;The danger points;109
8.2.2;Resistive mains cords;109
8.2.3;More than two leads;109
8.2.4;Spare conductors;110
8.2.5;Nothing certain yet;110
8.2.6;The safety routine;110
8.2.7;Don't relax your guard;110
8.2.8;Genuinely AC-only receivers;110
8.2.9;The isolating transformer danger;110
8.2.10;Other hazards;111
8.2.11;Fumes from solder;111
8.2.12;Chemical warfare;111
8.2.13;On your own;111
8.3;Chapter 18. A logical approach to fault finding;112
8.3.1;Initial tests;112
8.3.2;Look for previous work!;114
8.4;Chapter 19. Repairing power supply stages;115
8.4.1;AC-only receivers;115
8.4.2;Use the correct replacements;116
8.4.3;Low voltage negative bias;116
8.4.4;RF by-pass and other HT decouplingcondensers;117
8.4.5;AC/DC receivers;117
8.4.6;When the mains dropper fails;118
8.4.7;Resistive mains cords;118
8.4.8;Extra precautions necessary with AC/DCand part AC sets;119
8.4.9;Barretters;119
8.4.10;'Watt-less' droppers;119
8.4.11;Replacing 'metal' HT rectifiers;119
8.4.12;Dealing with energised loudspeakers;120
8.5;Chapter 20. Finding faults on output stages;122
8.5.1;Replacing output transformers;123
8.5.2;Watch out for negative feedback;123
8.5.3;Transformers with three windings;123
8.5.4;Some causes of low or distorted reproduction;123
8.5.5;What about the output valve?;124
8.5.6;Heater-to-cathode leaks;125
8.5.7;Push-pull output;125
8.5.8;Hot valves;126
8.5.9;'Crackly' tone controls;126
8.6;Chapter 21. Faults on detector/AVC/AF amplifier stages;127
8.6.1;General AVe problems;128
8.6.2;Detection and AVe in 'short' superheats;128
8.6.3;Indirectly heated double-diodes inbattery receivers;129
8.6.4;Grid leak and anode bend detectors;129
8.6.5;'Westector' diodes;130
8.7;Chapter 22. Finding faults on IF amplifiers;131
8.7.1;Deathly silence;131
8.7.2;Another source of self-oscillation;131
8.7.3;Beware;132
8.7.4;Repairing faulty or damaged IF transformers;132
8.7.5;Realignment with a signal generator;133
8.7.6;'Staggered' IFTs;133
8.7.7;Aligning with a wobbulator and oscilloscope;134
8.7.8;Beware of HT!;134
8.8;Chapter 23. Faults on frequency-changer circuits;135
8.8.1;A case in point;136
8.8.2;Faults on the aerial coils;137
8.8.3;When realignment is necessary;137
8.8.4;Optical bandspread;138
8.8.5;RF amplifiers;138
8.8.6;Rejectors;138
8.8.7;Image rejectors;139
8.8.8;Adjusting ferrite aerials;139
8.8.9;Faults on the tuning condenser;139
8.8.10;Tackling broken dial drive systems;139
8.8.11;Some common types of dial drive;140
8.8.12;Permeability tuning;141
8.8.13;Dial pointers;141
8.9;Chapter 24. Repairing American 'midget' receivers;142
8.9.1;Tackling faults on resistive line cords;142
8.9.2;Extra precautions necessary with midget sets;143
8.9.3;Types of midgets;143
8.9.4;Rectifiers and HT smoothing;143
8.9.5;No decoupling required;144
8.9.6;Output stages;144
8.9.7;Detectors in TRF midgets;144
8.9.8;RF amplifiers in TRF midgets;144
8.9.9;Detector/AF amplifiers in superhet midgets;145
8.9.10;IF amplifiers;145
8.9.11;Frequency changers;145
8.9.12;RF amplifiers in superhets;145
8.9.13;Aerials;145
8.10;Chapter 25. Repairing faults on automobile radios;146
8.10.1;Realigning automobile receivers;147
8.10.2;Can the polarity be changed?;148
8.11;Chapter 26. Repairing battery operated receivers;149
8.11.1;Conventional domestic and portable types;149
8.11.2;Fault finding;150
8.11.3;'All-dry' and mains-battery sets;150
8.12;Chapter 27. Oddities;151
8.12.1;Replacing the output valve;152
8.12.2;The Ekco BV67 (Figure 27.2);153
8.12.3;The Philips V7A;153
8.12.4;The 'monoknob' receivers;153
8.12.5;Philips and Mullard pushbutton receivers;155
8.12.6;The wartime civilian receiver;155
8.12.7;Meeting the specifications;156
8.12.8;An opportunity missed;156
8.12.9;The design of the prototype in detail;156
8.12.10;The AVC system
;157
8.12.11;The battery version;158
8.12.12;Breaking the mould;158
8.12.13;Likely problems in servicing;158
8.13;Chapter 28. Repairing FM and AM/FM receivers;164
8.13.1;Realigning FM and AM/FM receivers;164
8.14;Chapter 29. Public address and high fidelity amplifiers;166
8.14.1;Design features;166
8.14.2;Output powers;167
8.14.3;The Osram PX4 push-pull amplifier(Figure 29.1);167
8.14.4;The Osram PX25 (Class A) amplifier(Figure 29.2);167
8.14.5;The Osram PX25 (Class AB1) amplifier;167
8.14.6;The Williamson KT66 amplifier (Figure 29.3);168
8.14.7;Preamplifiers (Figure 29.4);169
8.14.8;Repairing amplifiers;172
8.14.9;Faults on and around output valves;173
8.14.10;Preceding stages;173
8.15;Common abbreviations;175
8.15.1;Ranges of frequencies commonly used in vintage radio;177
8.15.2;Some obsolete radio terms which may be encountered in old literature;177
8.15.3;Some colloquialisms used in vintage radio;178
9;Part 3:;180
9.1;Appendix 1. Intermediate frequencies;182
9.2;Appendix 2. Valve characteristics and base connections;196
9.2.1;Order of presentation;196
9.2.2;Interpreting receiving valve nomenclature;196
9.2.3;ADDENDUM TO TABLE 17;262
9.3;Appendix 3. How old is that radio set?;263
9.3.1;Clues inside the set
;264
10;Index;266

Leseproben

Chapter 1 Basic facts you need to know about electricity and magnetism
Electricity from batteries
There are two kinds of electricity, alternating current (AC), the kind that comes from the electricity mains, and direct current (DC), which is the kind that comes from batteries. Every battery has two poles or connections, one positive and one negative. Current drawn from a battery flows continuously in one direction only, hence the old alternative name of ‘continuous current’. Batteries may be subdivided into two classes known as primary and secondary types. Primary batteries produce electricity from chemical action within ‘cells’ which continues until the chemicals become exhausted and the battery ‘runs down’. There are various combinations of chemicals capable of producing electricity at various voltages per cell, but for our purpose we need only consider the ‘Leclanche’ type of cell used for torch and transistor radio batteries which produces 1.5 V. Two or more cells may be joined in a chain, positive to negative, to obtain any desired voltage for various jobs. Vintage radio sets used batteries of up to 165 V to provide power for the valves. Although they are not ‘dry’ (except when totally run down!) primary cells and batteries are commonly known as dry types to distinguish them from secondary batteries which employ acid or alkaline solutions. Secondary batteries also employ chemical action within cells to produce electricity but in this case the chemicals have to be activated (‘charged’) first by connecting the cell to an external source of DC voltage for a certain time. When charging is complete the cell will deliver voltage until the chemical action ceases, when it may again be recharged. This process may be repeated many times before side effects within the cell cause it to fail completely. The lead-acid type of cell used in vintage radio sets produces 2 V, and once again two or more may be series connected to provide higher voltages, although most of the sets you are likely to encounter use only a single cell. Figure 1.1 (a) The construction of a dry cell as used in batteries for vintage radio sets. Modern cells follow much the same pattern. (b) How numbers of dry cells may be connected in series to build up any desired voltage Alternative names for a secondary battery are storage battery or accumulator, the latter being the one most generally used in vintage radio. Figure 1.2 Various types of 2 V accumulator used in vintage battery operated receivers. Far left, a typical glass bodied accumulator with metal collar to provide a carrying handle. Centre, a celluloid-case type filled with jellied acid for portable sets. Right, another celluloid-case type but filled with ordinary acid for semi-portable sets Vintage radio sets made to operate on batteries usually employed a combination of one or more primary batteries and one accumulator to provide high tension (HT) and low tension (LT) supplies for the valves. Earlier sets also required another source of voltage for the valves to provide grid bias (abbreviated to GB, and of which more later) of up to - 16 V. From 1939 the introduction of a new range of valves known as ‘all-dry’ types made it possible to have receivers working from just two dry batteries without the need for accumulators. However, by far the greatest number of vintage receivers you are likely to encounter were made to operate from mains electricity and to understand how they worked it is first necessary to know the basic facts about how electricity is produced and its connection with magnetism. Electricity and magnetism
Magnetism was discovered some thousands of years ago when someone tripped over a strange piece of rock, picked it up and found that for some unknown reason it attracted to itself anything made of iron. What was more, if this rock was rubbed along a strip of iron it too started to attract other pieces of iron. Although this was interesting, no practical use for magnetism was found for some time – until around the year 1200 AD, in fact, when someone else discovered that if a magnetised needle was hung on a piece of twine it would spin around and settle into a position where one end pointed north and the other south. Now, this really was useful, because it enabled sailors to travel the world with a sporting chance of reaching their intended destinations and eventually returning home. It also brought about a rather contradictory piece of terminology. Not unnaturally the end, or pole, of the needle that pointed north was called the north pole and the one that pointed south the south pole. However, if two magnets are held close to each other the north pole of one is attracted to the south pole of the other and vice versa, hence the rule that unlike poles attract, like poles repel. Logically, this ought to mean that the pole of a magnet that points north isn’t really its north pole but its south, but as things then start to become rather confusing that part is conveniently overlooked. As for the rock which started the whole thing off, the old name given to it was lodestone or loadstone; lode/load in this instance coming from a old word meaning a way, hence a rock that shows the way. Nowadays it is more prosaically referred to as a form of iron oxide called magnetite. For the next seven hundred years or so not much else happened with magnets until electricity began to be studied in the early nineteenth century. It didn’t take long for scientists to find links between electricity and magnetism and thus unwittingly start the journey that would lead to electric light and power, radio communication, party political broadcasts on television and other advantages which we enjoy today. In fact, it’s a fascinating story that is worth investigating in specialist reference books but here we shall have to content ourselves with enough of the gist of it to give the basic principles on which vintage radio sets depend. What changes an ordinary piece of iron into a magnet is that when stroked with magnetite groups of its molecules called domains, normally pointing in random directions, are lined up to point all the same way. This effect can also be obtained by a different means, as we shall see in a moment. Magnets produce what is called a magnetic field. An experiment to demonstrate this, once familiar to school boys (perhaps it is still), was to place a magnet under a sheet of thin card, onto which iron filings were scattered, whereupon the latter would obligingly form themselves into exact patterns tracing out what are called the lines of force from the magnet, as in Figure 1.3(c). Figure 1.3 (a) Shows the domains in a bar of unmagnetised ferrous metal pointing in random directions. After magnetisation (b) the domains are lined up to point the same way, (c) shows the magnetic lines of force emanating from a bar magnet The sort of magnets we have been talking about are known as permanent magnets because once they have been magnetised by some means they remain so more or less indefinitely. Now for another type of magnet. If a length of wire is wound around a cardboard tube to make a coil, and its two ends connected to a battery, a magnetic field is set up in and around it. This can be demonstrated by placing a compass alongside the coil, when its needle will be deflected when the battery is connected and will remain so until it is disconnected. If a six-inch nail is placed inside the coil, when the battery is connected it will become magnetised because the lines of force from the coil will have lined up its molecules. The nail will remain magnetised for as long as the current flows through the coil but will revert to just an ordinary piece of iron when the battery is disconnected. This type of magnet is known as an electromagnet and it too produces lines of force that may be plotted with the aid of iron filings. Figure 1.4 Because a coil will induce magnetism in this way it is said to possess inductance, the unit of which is the henry, taken from the name of a scientist as are so many electrical and radio terms. Coils of any desired inductance may be produced by varying the number of turns and the gauge of wire used – and the material on which the coil is wound, as we shall see a little later. Figure 1.5 (a) The magnetic lines of force emitted by a coil through which current is passing. (b) Placing a piece of soft iron (such as a large nail) inside the coil greatly increases the magnetic force That is one aspect of the relationship between electricity and magnetism. Here is another. If that same coil of wire is passed at right angles through the magnetic field of a permanent magnet a voltage of brief duration will be induced into it, sufficient to be indicated on a sensitive electrical instrument called a galvanometer, which will respond to very small voltages or currents. If some means is found of maintaining constant movement of the coil the voltage will be maintained. In practice this is carried out by having the coil wound on what is called an armature which is mounted on bearings and free to rotate within the poles of a powerful magnet. This is the basis of the dynamo or generator which, when driven mechanically, will produce a steady current of electricity. Figure 1.6 Passing a magnet into a coil of wire induces a small voltage measurable on the galvanometer...