A Single-Ended 6550 Amplifier

Many articles have appeared regarding projects using one of the most sturdy, versatile, and trustworthy audio tubes ever made — the 6550. Most of them show these audio beauties used in the push-pull configuration in order to obtain the greatest efficiency and the most power output. In this article, the 6550 is used in a clean, sweet-sounding, single-ended design. The amplifier has very few parts, is easy to build and repair, and the cost of the project is nominal when you consider the kind of sound that is produced. This article was originally published in audioXPress, September 2001.

During InfoComm 2016, Allen & Heath has released a major firmware update for its dLive series, which includes Director software to enable offline editing and live mixing on a PC with or without a Surface, plus preamp modeling on all 128 channels, 5.1 surround sound, and dedicated Mute Groups. The announcement follows the recent introduction of a host of major enhancements to the feature set and ecosystem of its Qu Series of compact digital mixers.

In the February 2015 issue of audioXpress, Mark Driedger discussed a tube power amplifier controller based on the Arduino open-source microcontroller. In this follow-up article, Mark Driedger explains how to use some of the Arduino’s untapped capabilities to incorporate the bias meter into the amplifier controller with virtually no additional hardware. A temperature sensor and over-temperature shut-down capability are also included. This article was originally published in audioXpress, May 2015.

At the 2016 High End show in Munich, and as advertised, visitors could experience the relaunch of the Dynaco ST70 Series 3, stereo tube amplifier, together with the prototype of a new integrated Dynaco ST-1 amplifier. The return of the Hafler and Dynaco brands was signaled in Munich with the return of what is, without question, the most successful tube amplifier of all time. And the new advanced design was sounding great already.

This month, learn more on how Master Quality Authenticated (MQA) end-to-end technology is redefining the source for music. We interview Electro-Harmonix tube engineer Alan Otto, and Eminence’s Rob Gault and include a report on the CanJam SoCal 2016 show. We also discuss acoustic metamaterials, how audio cables affect the sound we hear, review the Dayton Audio OmniMic V2 acoustic measurement system, and feature a DIY project of an ecological power supply for power amplifiers.

This year’s High End show in Munich was a decisive moment for Master Quality Authenticated (MQA), the technology and the UK-based private company. Adopted by an increasing number of hardware and content partners, the revolutionary end-to-end technology that delivers master quality audio in a file that’s small enough to stream or download is now closer to become mainstream following the announcement that Warner Music Group and MQA have entered a long-term licensing deal.

60 years later, legacy brands Hafler and Dynaco, two of the most prestigious brands of all-time, have come together under the umbrella of Radial Engineering Ltd, Hafler’s former Canadian distributor - turned manufacturer. Since acquiring the brands in earlier 2014, Radial Engineering has been working on new Hafler designs and will now show the first Dynaco products at the High-End Show in Munich.

Here is an excellent beginner’s project for those just getting started in this hobby. This “little” amp is easy to construct and has only about 25 parts in each channel. The system transformers are very inexpensive, and the total cost involved for a complete stereo version should be very minimal! This article was originally published in audioXpress, December 2001.

Are you interested in tube projects? Then audioXpress May is for you. There’s amps and preamps for everyone in the best DIY tradition of Glass Audio. audioXpress May also offers innovation in new technologies, from software to audio networking and immersive audio, and this issue includes a nice combination of all these topics.

Here’s the final section in our series on parts reliability, how to choose them and how to estimate their life expectancy. In the third part of this article, the author continues to examine electronic components, and discusses what we can do about reliability. This article series was published in audioXpress, from November 2001 to January 2002.