Valves for Audio Frequency Amplifiers by GEC Co. Ltd - code 2002

Philips, one of the world's oldest manufacturers of vacuum tubes, offered this manual for enthusiast constructors in 1954. It is part of the Philips Technical Library which covered almost all elements of electronics design both at the practical and theoretical level. This is a practical volume which begins with a clear set of rules of thumb for building audio amplifiers of very high quality. These are practical pointers for keeping hum, noise, interference and heat in sufficient control to avoid noisy and destructive operation. Next the author takes the reader on a tour of those valves (tubes) offered by Philips (and other manufacturers) specifically designed for high-quality audio uses. These tubes include EF 40, EF 86, ECC 40, ECC 83, EL 34, El 84, and GZ 34. Each tube's full performance specifications is included allowing the user to re-design any amplifier to a different operating format.

The author then offers a chapter on just how to use the operating data provided, including practical examples. This includes both control amplification for volume level and tone controls as well as input and power stages.

Components and circuits are the topics of the next chapter, beginning with a thorough and clear discussion of feedback, tone control, the output transformer, amplifier input circuits, microphone, gramophone pickups, and loudspeaker.

Chapter 6 is the largest of the book offering amplifier designs ranging in power from a single ended 3 watt to a 100 watt Class B. These include also an 11 watt EL 84 push-pull, a 10W EL 34 push-pull, class A, a 15W AC/DC using PL 81 outputs, a now classic 35W EL 34 push-pull in class AB, a second 35W EL 34 class AB design with tone and volume controls, a 70W class AB using four EL 34s and finally a 100W class B using two EL 34s. All eight of these amplifier designs is fully described in the text and the features of each discussed in depth. Each amplifier diagram is supplied with full measurements for performance as well as data on the transformers used, with instructions in some cases of how to make both power and output types.

The book's appendix covers all the then current tubes for use in amplifiers, a valuable reference for vintage equipment restorers.

Valves for Audio Frequency Amplifiers was written at a time when audio amplifier design had reached a new peak of quality and performance. It still provides an excellent guide for the enthusiast who wishes to rediscover the satisfactions of audio reproduction with tube equipment.

key topics

• Construction hints
• Valves for various stages
• Use of valve data
• Components and circuits
• 3W gramophone amp
• EL84 push-pull amp
• EL34 single-ended amp
• PL81 15W push-pull amp
• EL34 35w push-pull amp
• 70W EL34 p-push-pull amp
• 100W class B EL34 amp

book specifications

• paperback
• black and white print
• 144 pages
• 145mm x 202mm
• 230g

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