You Can DIY! Meet the Pentriode

This DIY-focused article introduces the Pentriode, a concept to explore the familiar idea of connecting commonly available pentode tubes as triodes, creating a circuit that excels in linearity. 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 the author previously wrote about for audioXpress. This article was originally published in audioXpress, May 2022.

Schiit Audio is promoting the 10-tube Folkvangr, its first limited-edition headphone amplifier. The first DC-coupled, output transformerless (OTL) and output capacitorless (OCL) headphone amp, Folkvangr also includes an 8X impedance multiplier to increase versatility with low-impedance headphones. Limited to a 250-piece run, the Folkvangr headphone amp is priced at $1799, including a full complement of input and output tubes.

It's time for the Glass Audio/Tube Focus edition of audioXpress. In this issue, Michael Boele shares his long-term review of a pair of 2021 new production Western Electric 300Bs, Merlin Blencowe explains how to add Bluetooth to a Tube Amp, and Alan Kimmel introduces us to the possibilities of the Pentriode. There's also a Market Update report on vinyl sales and the latest trends in turntables and cartridges, as well as a review by Stuart Yaniger of the latest Orchard Audio Starkrimson Stereo Ultra GaN-based amplifier.

Tube arcing is not necessarily a result of a "bad" tube or a "bad" design. It is far more likely the result of using the tube longer than you should for the application you’re using it. This interesting article, published in audioXpress, November 2004, remains a great read. At the time it also originated a response from Eric Barbour and Ed. T. Dell regarding their experience with cathode stripping.

More than a decade since the original publication by audioXpress, many readers still actively search for information and share the schematics of this OTL tube project. Tim Mellow's design explores a different output stage using a novel combination of local feedback and current drive in order to achieve good symmetry and cancellation of even harmonics. This article was originally published in audioXpress, February 2010.

Zesto Audio, the Californian company founded by George Counnas, announced the launch of a new Class A amplifier design that offers an impressive 100 watts per channel (8 ohms) plus a unique feature of a three-position "Auto Bias Select" switch. In order to achieve its power rating, the new Bia 200 Select Stereo Power Amplifier is sold with four 12AU7 plus four matched KT150 output tubes. Thanks to the new auto bias switch, the amplifier is ready to safely accommodate KT88, KT120 and KT170 tubes, delivering options for all preferences.

The February 2022 edition of audioXpress is now available and features our annual Market Update on Microphone technology. Vikrant Singh Tomar discusses TinyML and Voice Recognition Technology On the Edge, Richard Honeycutt writes about Quantification of Speech Intelligibility, and Mike Klasco expands on audio applications for Haptic Devices. George Ntanavaras builds a phono and line/headphone amplifier project, Brian Bylenok proposes a refined Current Feedback Headphone Amplifier, and Richard Honeycutt reminds us that Tube Power Amps also have Classes. Now available in print and online.

audioXpress readers have long been anticipating the announcement, and Western Electric finally confirmed that the company is taking orders for the new 91E integrated amplifier. Following the resumed production of the 300B triode tubes at the modern Rossville Works facility, Western Electric now launches a single-ended (SE) high-fidelity amplifier inspired by the 91A, its famous predecessor used in early Hollywood motion pictures. The new SE design offers over 20 watts per channel - a first for the 300B in a totally new design for the 21st Century.

McIntosh, the prestigious home entertainment and ultimate-quality audio brand for over 70 years, announced the MC3500 Vacuum Tube Amplifier Mk II, a tribute to the original that inspired a generation of musicians and music fans alike. Originally used to power the sound system for Woodstock '69 amongst other formative music events, the iconic monoblock amp was recreated by McIntosh’s expert team of engineers and designers to include modern upgrades that celebrate the brand’s rich history.

The November 2021 edition of audioXpress looks at the latest industry trends in digital signal processing, and enabling fully adaptive audio DSP experiences. Roger Shively (JJR Acoustics) writes about how the unique acoustic space of the car interior can be defined by the use of DSP, and Al Clark (CEO, Danville Signal Processing) shares his company’s journey into the development of the dspNexus DSP Audio Processor. Now available for viewing online, download and in print.