It's time for the Glass Audio/Tube Focus edition of audioXpress, always one of the magazine's most popular issues. And this year, the focus is even more relevant given the changes that are taking place in the availability and prices of tubes. As noted in this month's editorial, we are a long way away from the years that inspired the Glass Audio magazine, when large quantities of new-old stock (NOS) and new, cheaper tubes from Russia and China flooded the market. As a result of the disruptions in the supply chain and increasing costs resulting from the effects of the global pandemic and geopolitical events, tube manufacturing was profoundly affected. While the tubes used for audio applications will remain in demand, the number of suppliers has never been lower nor have the prices been higher.
As a consequence, this also creates an ideal combination for companies such as Western Electric to resume manufacturing tubes again in the US. Having started with a flagship product aimed at the higher end of the audio market, Western Electric has successfully resumed manufacturing 300B tubes in its state-of-the-art Rossville Works in Rossville, GA. As audioXpress has reported, that Western Electric facility is now equipped to also handle production of multiple tube types.
And while Western Electric works on that much needed expansion effort, audioXpress May 2022 shares what the company has achieved with the new production 300B. In an exclusive review for audioXpress, renowned tube expert Michael Boele, details the proof in his long-term review of a pair of 2021 new production 300B directly heated power triodes. For 10 months, Boele had the opportunity to live with and extensively use a pair of these 300Bs and his impressions and extensive testing could be directly contrasted with the considerable collection of 300B tubes - Chinese, Russian, Czech and Slovak clones, as well as several pairs of Westrex/Western Electric reissues produced in the Kansas City factory in the late 1990s, and two “old stock” Western Electrics. The article - now also available online here - offers the most complete depiction of the Western Electric 300Bs' behavior and qualities.
And as a bridge between classic tube designs and the present, Merlin Blencowe, the author of an excellent collection of books about tube amplifiers and an analog design engineer working for AMS Neve in the UK (yes, the studio consoles!), offers a DIY project to add "Bluetooth to a Tube Amp." We know that some people might find it heresy, but these days we can buy tube amps with Bluetooth, and even Wi-Fi or LAN connectivity installed. In this article, Blencowe details how to derive the +5V needed for a Bluetooth module from an existing heater circuit. And he also offers valuable tips on "Accommodating Different Valve Heaters."
In another valuable DIY-focused article, Alan Kimmel introduces us to the Pentriode, a concept to explore the familiar idea of connecting commonly available pentode tubes as triodes, creating a circuit that excels in linearity. As he explains, "a pentode can function as a triode when its screen grid is connected to the plate. When triode connected, many pentodes can be outstanding very linear triodes. The Pentriode is formed by making one simple change to connect the screen grid to the cathode of a cathode follower." The article proposes different possible approaches, including for a mu stage, a design that Alan Kimmel previously wrote about for audioXpress.
The next article in this issue, also focused on tubes, comes from Mark Driedger, concluding a two-part text on "Testing Vacuum Tubes." While Part 1 of his article covered how tubes fail and wear out, and their key characteristics, in this continuation he expands into how tubes are tested, the different types of tube testers, and how to select a new, commercially available tube tester. This is a much needed update on a topic that never gets old, providing valuable information and excellent references for further reading for those interested.
And this wouldn't be the Glass Audio special issue of audioXpress without our own Richard Honeycutt sharing his considerable knowledge in his Hollow-State Electronics column. For this month, he proposes an overview of "Graphical Analysis of Class-A Amplifiers," and how to design an audio amplifier and achieve the best performance out of existing tube-based circuit designs using the graphical analysis method. This article hits close to the heart of most tube-amp designers and discusses optimizing for B+ supply voltage; voltage gain; and distortion behavior, eventually aiming for a Class-A stage.
And because tube amplifiers almost always go hand-in-hand with record players, this May 2022 issue also includes a Market Update report about "The Enduring Appeal of Vinyl." Sales of vinyl records are again a respectable revenue source for the music industry, representing more than $3.4 billion of the $26 billion USD in global revenues achieved in 2021. No wonder, the audio industry is responding with new products for all price segments. Apart from providing the latest market indicators, this report details the state of the industry both in terms of music sales and playback technology for vinyl records. A discussion of trends in the entry-level, mid-level hi-fi turntables and cartridges, and the premium high-end segment that is seeing a lot of comebacks from famous brands.
Of course, we also need to look forward at emerging audio electronics, this issue offers a review of the latest Orchard Audio Starkrimson Stereo Ultra by Stuart Yaniger. This amplifier, designed by Leo Ayzenshtat, the company's founder, uses GaN Systems’ gallium nitride (GaN) power transistor technology, which Yaniger evaluated for audioXpress in the April 2022 issue. As an early adopter of GaN, Ayzenshtat thought to explore the latest transistors from GaN Systems to design an audio amplifier that could achieve the best possible hi-fidelity results. And Yaniger listened and measured the Starkrimson Stereo Ultra, being able to contrast it with all the latest Class-D contenders.
And there's much more. In this issue, Ethan Winer returns with another chapter about "Building a Guitar-Controlled Synthesizer." This is the second article in a fascinating DIY journey of a guitar-controlled, all-analog synthesizer project that will include multiple stages and modules. Following a sample and hold circuit designed to translate the guitar notes to equivalent oscillator frequencies, this article details voltage control and how the playing is converted to voltages and back to frequency.
And from synthesizers to acoustics and sound reinforcement, in his Sound Control column, Richard Honeycutt discusses the "Effect of Air Conditions on Sound Propagation." Sound systems need to be readjusted under variable atmospheric conditions, as temperature, relative humidity, and barometric pressure changes. This article discusses how these conditions affect different acoustical parameters and what can be done - and where - to adjust for the changes.
Remember, every month, audioXpress brings innovations in audio, different topics in audio electronics, and the best in DIY audio, published 12 times per year, and available in print and online. Subscribing to the digital online version allows immediate access and is available here: www.audioxpress.com/page/audioXpress-Subscription-Services.html
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