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I've been working with John Soriano of Apos Audio on a number of recent equipment reviews, and through our regular contacts, I discovered a few months ago that Apos would soon be marketing their own line of self-branded premium vacuum tubes. That news excited me to no end, especially when I learned that among the... Read More »

The Zesto Audio Leto Ultra II Preamplifier Now celebrating its 13th anniversary of producing award-winning all-tube designs for audiophiles, California's Zesto Audio has introduced its most advanced preamplifier to date. The Leto Ultra II Preamplifier is the amazing George Counnas's assault on the state of the art in all tube topology, and the third incarnation of the... Read More »

Greetings friends, I hope you are doing well! In August of 2019 the Shuguang Electron Tube Factory was shut down in preparation for a move to a new location. By March 2020 the World Health Organization declared Covid-19 a worldwide pandemic, which would result in the shut down of most vacuum tube production still operating... Read More »

The brilliant late audiophile, J. Gordon Holt, once wrote that if the purchaser of a fine system was torn between buying a great pair of speakers or a great amp, one should choose a great amp and a good pair of speakers that fit your basic needs. He commented that he had heard numerous systems... Read More »

A friend of mine was looking at these Sophia Electric vacuum tubes, and she told me "They're so pretty, they look like works of art."  These Sophia Electric vacuum tubes really are works of vacuum tube art. The Sophia Electric 45 mesh plate triode (above) and Aqua 274B rectifier (below) vacuum tubes are not only... Read More »

Most tube electronics enthusiasts are content to live with the stock tubes chosen by the manufacturer. And yet for others, comparing various types and grades of vacuum tubes into audio equipment poses an endless point of fascination, as they impart different qualities on signal passing through them, thus affecting the listening experience; some are more... Read More »

It has been quite some time since my last article for Positive Feedback about the Sophia Electric vacuum tubes developed and offered by Sue and Richard in McLean, Virginia. It was all the way back in August of 2017 that I wrote about the Sophia Electric EL34-ST (photo below) and Aqua 274B vacuum tubes (HERE),... Read More »

I've always enjoyed visiting with Richard and Sue at Sophia Electric about their vacuum tubes and amplifiers, so when Dr. David contacted me about Sue's inquiry to see if I'd be interested in writing about the new Sophia Electric EL34-ST and Aqua 274B vacuum tubes, I said, "You bet!" I'll start with the new Sophia... Read More »

This article, by Harvey Rosenberg, originally ran when Positive Feedback was in print - Vol. 7, No. 6, 1998. During my short tenure as PF's Techno-Shaman of Coolosity I have suggested that you, while artifying your harmonic/space/time continuum in your expanded aural matrix, consider single-ended triode amplifiers with tube regulated power supplies, Nobu Shishido's Inverted Interstage... Read More »

Since the modification to my solid-state Reference Marantz integrated amplifier more than a few years ago, my tube amplifiers have been gathering dust. My modified PM15S1 has been getting the lion's share of the musical stage at my house. But a recent upgrade of my Margules U280SC to 25th Anniversary Edition has changed all that.... Read More »

Now that I have highlighted the systems that for me were the top of the show, I will now turn attention briefly to a few systems that were still affordable by us mere mortals, and not just showcases in excess. By "affordable" I mean a system that comes in at less than the price of... Read More »

I love and appreciate tube based audio gear and own sixteen pieces of tube gear between my two reference systems. Without a thorough knowledge of tube types and their substitution possibilities, you may be over-paying for your new or NOS tubes you employ, or just pick the wrong ones. This data is based on my... Read More »