You Can DIY!: Repurposing an Old Preamp for Line-Level Duty

This modification and restoration article shows how to preserve the best features of unused tube equipment. The article describes a tube preamplifier that the author wanted to position at the input to his home power amplifier, eliminating the need to adjust his 1972 McIntosh MX10 tuner and 240 power amplifier’s volume high when he wants to fill his home with music. In this case, an old Shure Model 65 stereo conversion preamplifier using two dual-triode 12AX7 tubes provided an excellent platform for the project. This article was originally published in audioXpress, May 2020.

Our May 2021 Glass Audio Special edition is certain to inform and inspire you. We reveal what is happening at Western Electric's new Rossville Works in Georgia, where production of 300B tubes is ongoing, we explain how to draw tube load lines, and we offer a valuable preamplifier design that enables you to compare the sound of tube and solid-state circuits from the same audio source. There's also a versatile stereo tube amplifier design to build, and plenty more audio electronics theory and practice in this edition. Now available online and in print.

In this article for audioXpress, Bill Reeve helps us to make sense of a misunderstood circuit. A capacitance multiplier is useful as a power supply low-pass filter. It is commonly said that, like Miller capacitance, the capacitor’s value in this circuit is “multiplied” by the transistor gain (β) to lower the filter’s pole frequency. The transistor-enhanced filter does that and more, as the article explains in detail. This article, an excellent tutorial on analog circuit design, was originally published in audioXpress, August 2012.

audioXpress May 2020 Glass Audio/Tube Focus edition is now available. Highlighted on the cover is a review of the RødeTest FuzzMeasure Audio and Acoustic Measurement Software and Ethan Winer's experiments to measure capacitor distortion. For tube enthusiasts, Bill Reeve repurposes an old Shure preamp for line-level duty, and Bruce Heran details how he built his two Mini Blocks tube amplifiers. Mike Rothacher shares an inexpensive MOSFET Follower (MoFo) Class A amplifier project, Richard Honeycutt provides valuable lessons about repairing guitar amplifiers, and there's plenty more audio electronics focused articles. Download now!

For audioXpress May 2019 -Glass Audio Special - we’ve put together a very strong edition, with some of best tube experts sharing a series of DIY projects for all skill levels, from restoration projects to new amplifiers, preamps, and headphone amps. We review the Nu:Tekt HA-K1 headphone amplifier using the novel Korg Nutube 6P1 device, and interview the founder of Parks Audio. We go deep on measuring voltage regulator ripple rejection and we even look at square-wave testing. All inside audioXpress May 2019!

In this article, Bill Reeve explains how to drive tube heaters with a constant current to lengthen the life of your vacuum tubes. As he explains, obviously, the best way to extend your amplifier’s vacuum tube life is to never turn it on. Some would say that the second best thing you can do is to never turn it off. The third and fourth options may be to gently turn on the tube heaters and not leave the B+ voltage on when the heater voltages are off. This article was originally published in audioXpress, May 2014.

In this article for audioXpress, Bill Reeve discusses “An Alternative to Linear Regulators.” A project were he searches for equivalent power-line ripple rejection with less power dissipation, using a source follower-based (SFB) low-pass filter. Because no one wants to listen to an audio amplifier that hums. This article was originally published in audioXpress, April 2014.

Antique tube radios are some of the most coveted vintage electronics any audio enthusiast can acquire. They sound absolutely great, both as for what they are intended - to work as a good old analog radio - but also as an amplifier for external audio sources, including any digital source. In this audioXpress article, from May 2012, Bill Reeve shares how to approach such projects and provides excellent advice.

Bill Reeve’s article, “Repurposing Antique Radios as Tube Amplifiers,” provides vintage radio resources, simple circuit diagrams, and essential part info. He also covers the topics of external audio mixing and audio switching. The article appeared in the May 2012 edition of audioXpress magazine.