Ray Tubes Launches Select 5U4 Rectifier Tubes

Ray Tubes added another tube model to its Ray Tubes Select Collection. The Oakland-based vacuum tube company expanded its line-up with new-production 5U4 rectifier tubes in its Select Collection Rectifiers. Although the 5U4 aren't always top-of-mind, they’re a crucial component of tube amps for high-end audio, besides being an essential component in guitar amplifiers, prized for its ability to handle high peak currents. Select 5U4 vacuum tubes are now available from Ray Tubes' global network of retail partners.

Ray Tubes announced new-production 12AU7 tubes in both its Core and Select Collections. With this addition, Ray Tubes is now supplying the most common vacuum tubes, including the 12AU7, 12AX7, EL34, 6SN7, KT88, and 300B, all available through its network of retail and brand partners. All products from Ray Tubes are designed and tested specifically for audio applications and come with a one-year warranty, which is a great assurance compared to the risks of buying New-Old-Stock items.

The original Mu Stage project, published in Glass Audio in 1993, remains a popular build, serving the author's purpose to "combat listener fatigue." His Type 2 Mu Stage, published by audioXpress in 2019, introduced a streamlined version with added capabilities. Now, the new Type 3 Mu Stage resulted in what the author believes to be a breakthrough, improving the realistic reproduction of music. This latest iteration of the circuit was prototyped by Kim Bond, an enthusiastic builder of the previous Mu Stages.

This extensive, 428-page, self-published hardcover book, is much more than another publication on tube amplifiers. As Jan Didden discovered, this book contains all the knowledge needed to check how an input low-pass filter must be dimensioned, how to investigate the different resistor types and their properties, capacitor types, which tubes to use, how to bias them, and construct the load lines, and even how to design low-noise power supplies. A one-stop resource for tube-based audio power amplifiers, and clearly a work of love!

This year’s special Glass Audio issue of audioXpress includes interesting explorations such as the Ultra-Linear Power Amplifier by Rudolf Moers, Micro Details in Push-Pull Output Transformers by Hans Polak, Getting Less Gain From Tubes by Merlin Blencowe, and the Type 3 Mu Stage Breakthrough by Alan Kimmel. This issue also includes two speaker designs from Ben (Wolf) Shaffer and Ken Bird, an article about the intriguing return of 78 rpm records, and Paul Marchese’s Part 2 of his insightful Primer on Class-D Amplifiers. Richard Honeycutt shares how he learned to DIY with Tubes.

Schiit Audio continues to expand on its vision to design sensible hifi with innovative features. That includes expanding its Forkbeard complete control products with the announcement of the Stjarna and Skoll F phono preamps. Stjarna is an all-out, limited-production, all-tube design that offers top-of-class performance, while Skoll F adds Forkbeard to the company’s existing all-discrete, zero-feedback, high-voltage-rail phono preamp.

The Orange Valve Tester MKII is a new microprocessor-controlled testing system from the famous British guitar amplification manufacturer. Featuring greatly improved algorithms with an updated database containing the test results of literally hundreds of new, used, and faulty valves, this MKII tester requires no knowledge of valve theory. A user simply inserts a valve into the correct socket, selects the valve type from the list, and presses the ‘OK’ button. The status of the valve under test is quickly revealed.

In their 30th year as a company, Tube Amp Doctor has expanded its REDBASE tube family with a new exclusive and high-quality premium tube model, the entirely new TAD KT88-STR REDBASE. TAD just announced that they now have stock of the newest addition to the REDBASE-tubeline - the KT88-STR REDBASE. And the best news in these times is that the new tubes are ready to ship worldwide, meeting the strong demand for heavy-duty KT88 tubes!

In this Glass Audio special issue, Menno van der Veen brings us his latest Vanderveen TRANS-PP80 Valve Amplifier, Tom Perazella remakes a famous (Z)OTL amplifier with 300Bs, and Peter Dieleman debunks recurring myths in tube circuit designs. Stuart Yaniger reviews the Hypex NCORE NCx500 amplifier module, while Burkhard Vogel expands his article on Vintage Op-Amp Noise Simulations, and Bruce E. Gillingham concludes its unique MB1 Monoblock Power Amplifier with Precision Bias Control.

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.