Elektor Special Project: Tube Amplifiers and Hi-Fi - June 2010

Introduction

Infection Desired!

It wasn't long ago that the fear of swine flu was rampant, and the World Health Organization declared it a pandemic. However, the population's composure kept the virus's spread in check and the pandemic within limits. Undoubtedly, the risk of infection was present and also realistic – but it did not create the panic reaction hoped for (and even desired) in certain circles. In stark contrast, you have allowed yourself to be infected by the tube virus again and are holding the right medication in your hands with this sixth special tube issue. Like the previous five special tube issues, this sixth issue is packed with information, fundamental knowledge, technical details, and schematics.

Semiconductor technology – as good and important as it is – initially pushed tube technology into the background, but never completely eliminated it. Especially in the audio and Hi-Fi sector, tube technology has risen like a phoenix from the ashes. Even though renowned tube manufacturers closed their factories in 'old Europe,' new production facilities have emerged in 'new Europe' and beyond due to the reawakened interest in tube equipment. It is interesting to read how the tube virus is spreading and how it affects production and manufacturer activities.

The EL 156 single-ended Class A amplifier showcases the uniqueness of this tube. Developed and built by Telefunken in Ulm, this legendary low-frequency power pentode found its primary use in professional amplifier systems thanks to its robustness. Its elegantly shaped glass envelope, as well as its outstanding low-frequency characteristics, hold a special appeal. The circuit is designed for the EL 156 produced in China on original Telefunken machinery, which, unlike the historical predecessor, is equipped with the common octal socket and wiring similar to EL34, 6L6, KT88, and similar tubes. Comparisons with the original Telefunken tube revealed that the replica is mechanically and electrically well-executed, thus justifying the development of a single-ended Class A amplifier.

Further highlights in this issue include a headphone amplifier that meets safety requirements and caters to the impedance needs of dynamic headphones.

A good tone control network is crucial for how well a guitar amplifier sounds. An article here describes that there is still plenty of room for improvement in tone controls.

For those who have been infected by reception technology, they can build their receiver with the superheterodyne – a somewhat more demanding project.

So, allow yourself to be infected by the many interesting contributions in this issue. We in the editorial team are already infected and have begun preparing the seventh special tube issue.

By the way: information on special tube issues 1 to 5 can be found on the Elektor website at www.elektor.de.

By Raimund Krings

Neuheiten (News)

6 News from Tube Manufacturers

Grundlagen (Fundamentals)

10 On the Trail of Sound
16 Effect and Application of Getter Materials for Vacuum Tubes
21 Sound Manufacturers and Sound-Influencing Elements in Audio Amplifiers

Praxis (Practice)

28 Single-Ended Class A Amplifier with EL 156 in Triode and Pentode Configuration
34 Headphone Amplifier with Output Transformer
40 More Sound
50 My First Super
62 Mains Filter
67 Measuring Filter

Technik (Technology)

72 Measurement Results Relative, Absolute, and Interpreted
79 Which Tube Sounds Better?
84 Modern Hi-Fi Technology and DIN 45 500

Info

4 Tube Amplifiers, Energy Consumption and Recycling
37 Advertiser Index
88 Tube Data with Socket Configurations
90 Imprint

Image Descriptions

Image 1: A vintage vacuum tube with a glass envelope and metal base.

Image 2: A close-up view of a human ear.

Image 3: Abstract, colorful, wavy lines suggesting sound or electronic signals.

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