The 2A3 Tube Amplifier - A Tribute to Simplicity and Warm Sound

"There is nothing quite like a quality tube amplifier," states the author in the introduction to this directly heated triode amplifier project. The idea for the amplifier started from the author's discovery of the Loftin-White circuit. The author chose the 2A3 directly heated triode power tube to implement the Loftin-White circuit. The 2A3 vacuum tube is a power triode capable of outputting 3.5 W in a single-ended Class A configuration. This article was originally published in audioXpress, August 2013.

This article focuses on the Poddwatt Series II stereo integrated valve amplifier, a project with roots that go back several years. The design continues to be relevant and to evolve. I call the basic design an “Oddwatt” because of its “odd” configuration, using two stages. This article was originally published in audioXpress, May 2013.

Recently, I got bitten by the nostalgia bug and picked up a pair of old factory-wired Dynaco ST70s in pretty nice condition. On one of the Dynaco ST70s, I installed a new 6GH8 driver board instead of dealing with the rare 7199 issue, and I designed a small (3” × 3”) PCB to combine the bias supply and added the LED bias-setting circuit. This article was originally published in audioXpress, April 2013.

When this great tube amp project was published originally in Glass Audio magazine, Ed Dell wrote “Joseph Norwood Still is pushing the envelope. His most recent triode design, which features the Svetlana 6550s and Hammond transformers, establishes new output limits—up to 100W.” Indeed, this would become a very popular project at the time, and still is, considering the frequent references. This article was originally published in Glass Audio 3, 2000.

This Class A tube headphone amp project, which the author created for Vintage Audio, includes a 6SL7GT for the input stage and a 6AS7G for the driver, and is able to drive headphones with impedance at or above 64Ω. The article provides a full description of design fundamentals and some useful guidance on the construction process. The result, as the author describes, should be “a satisfying headphone amp that will provide years of enjoyment.” This article was originally published in audioXpress, June 2008.

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.

The July 2016 issue of audioXpress is now available and includes something for everyone. We visit Sinar Baja Electric — the birthplace of speaker driver brand SB Acoustics, report on AXPONA 2016, Mark Driedger shares his amazing D70 Stereo Tube Amplifier project, and we explain how to test Dante-enabled audio devices. And that’s just the start! Download the July 2016 issue now!

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.

In a nod to the Maker Movement, this project uses a common open-source microcontroller module, the Arduino, to build an automatic power controller for a tube power amplifier. The resulting controller is very simple — a $25 Arduino module, a couple of dual op-amps, a few other components, and a 5-VDC power supply plus some opto-isolated switches. This article was originally published in audioXpress, February 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.