Single Ended Telefunken RE604

OK folks, here is the most exotic, most esoteric, and most mysterious amp on these pages so far. A Finemet iron, Tamradio input, Western Electric choked, 100 volt Japanese single ended amplifier based around the ancient and largely unknown RE604 power tube. Designed and produced by Telefunken in the late 1920’s to early 1930’s, the RE604 was sort of the German version of the American 45, making 1.5 -2 watts of what is perhaps the most euphoric audio output power ever produced. Readers of this page will know that I am a life-long fan of the UX-45 triode, the Godfather of single ended hifi. But the 45 might have met it’s match in Telefunken’s earliest globe RE604.

This is a very carefully crafted, no barrier, single-purpose item. And that purpose is 1.5 watts of supreme audio reproduction. Surely the output of this amplifier is among the tiny fraction of top designs and builds that transcends, or suspends, belief. Eyes closed it makes one really feel the performance in a visceral way, feeling immersed and surrounded, and more than anything, involved. Listening to this amplifier on my Rullit Aero 8 drivers, I’m impressed with the sense of space, a feeling of “being there,” that the RE604 delivers so effectively. And you can hear it immediately. You are there in the studio as Blossom Dearie is at the piano with her musicians spread out around her. Its 1957, and you are sitting there in a smoky little room in NYC. Then Anoushka Shankar comes in with a shimmery brush of the Sitar, and you are off to another deeply immersive experience. Even way off axis you can hear the depth of the space. It’s like a big open door.

One of the things I notice these days when I’m thinking about an amp or speakers is how it sounds (and feels) coming into or leaving my little room. Most combinations do sound really good, but some are also special in some way. For some strange reason I now look out for this effect. I’m not sure what this is good for, but for whatever that measurement is worth, this RE-604 amp really excels in that department. Coming down the stairs and rounding the corner in the front lower room you can feel its presence and it grows steadily as you get closer, sounding really good, and then coming into the room and entering the big “sweet spot”, which is golden, it’s really remarkable. Like you stepped into the music. This build has finesse, but this is still a muscular sounding amp. Tracks with heavy reverb take on a Platinum glaze. If sound made a visual impact like a heat signature does, and you could wear something like night vision goggles to “see” sound, I wonder how it all would look? Bright as hell through the RE-604.

In addition to a new and exotic power tube, this amp uses quite barrage of new (to me) input tubes. VR37, REN904, MH4, A410. None of these tubes were on my radar before this amp hit my studio. And I’m absolutely in love with a pair of Philips mesh plate E424 from the late 1920’s. Once again I’m finding myself in a place I’ve been before, perhaps from a different angle this time, but the question is the same. Is there more “ultimate” than this? I do feel in some ways that I am at an endpoint with this RE604/mesh plate REN904.

Above all, I feel very privileged to have owned and experienced a single ended amplifier of this caliber. This really is a penultimate audio experience. With the small effort I have made in building my own speakers and cables, and in room treatments, and the luck involved in just having all of it…this is like the final icing on the cake. I’ve been watching big builds like Thomas Mayer and Shindo for years, admiring and coveting, but also knowing I will never invest the big money required to get into one of their builds. I’m all about the coral-holey-basket level of return on investment, but this beautiful work of audio art launches my experience past perhaps even those milestones. This build has so much Karma. Whoever made this did it with thought and dedication, and with love. Thank you mystery builder. If you are lucky enough to encounter the RE604, I advise you to jump in with both feet. Super highly recommended.

A busy but clean build, someone put a lot of thought into the parts selection for this amplifier. Its simple, and overall very cleanly assembled, but DIY enough in character to be clearly a personal project. This is the best kind of single ended amplifier folks! Someone invested themselves into dreaming this up, carefully and laboriously gathering the objects (perhaps over a span of years) and then making it all a reality. Who else is building amplifiers based around obscure 100 year old German power tubes? Only a hobbiest, or perhaps a Shindo / Yamamoto / Kurashima level of cottage industry master.

The input tube here are Valvo REN904 globes. A lot of these early European tubes were coated in some kind of material, a thick paint of some kind. This pair certainly seems to have had a rough life.

Tamradio input transformers.

Western Electric chokes.

Finemet output transformers.

Unpotted output transformers like this certainly have an interesting look.

This amp uses a nice variety of input tubes. Here are: 1920’s mesh plate Philips E424, Valvo A4110 / REN904, and Mullard MH4.

Here in relation to the RE604 power tube.

The RE604 globes have a very interesting plate structure in comparison to the American tubes of the era, like the 71a and the 45. Its construction seems most similar to the Type 10. I believe this is the earliest example of the RE604, dating to 1928 or so, and these first globes had a complicated Adzide coating process that was abandoned in later versions. Today a company in South Korea, Stradi Tubes, has recreated the RE604, as well as a number of other archaic European tubes. I will eventually get a pair and report back.

A beautiful tube!

I always love the mesh plate tubes!

This amp is a 4 volt amplifier, like all European amps. USA amps are mostly 6 volt. At any rate, the rectifier here is a 5X4, a 4-volt version of the 5U4 and another tube I’d never heard of before. This is the only American tube on the amp.

In comparision to single ended 6L6: I love the 6L6 tube. And frankly the better examples of the 6L6 (which are for me the original KT66, 807, and 6BG6) do 98% of what a good triode does, and make 2-4 times the power. And I assure you Dear Reader, the 1930’s Visseaux 6L6G pictured here are a flat out superb version of the early 6L6. But the RE604 shows clearly in the first few seconds what the finest triodes do that set them apart from even the best of the pentode and tetrode sound. It’s a spooky clarity, a warmth, and a sense of relaxed space that effortlessly pushes every detail out into the room to float in front of you. The RE604 tube has a good splash of the 10’s clarity, while having warmth like the 300b and the balls of the 45. I feel almost like it’s the best 2A3 I’ve ever heard. And there is no downside that I can hear so far.

In comparision to the 71a: Back to back with Toshi Kurashima’s 71a, they are similar. In sound, they are like siblings. The RE604 is brighter, the 71a is a little thicker. The 71a has somewhat less space than the 604, but both are big imaging amps. The 71a’s image is smaller in scale than the 604. The 604 has way more power than the 71a, so the preamp needs to have some gain to make the 71a shine on my speakers, while the 604 works well even with a passive. The 604 is perhaps the winner here but both are so incredibly fine. These high end Japanese builds all seem to achieve the coveted absence of tension.

In more than 20 years of exotic audio obsession, this may be the ultimate so far. 1920's Philips E424 mesh plate globes driving 1920's Telefunken RE-604 globes. Wow this is a saturated, powerfully deep sound. But its ethereal and light-footed too. Wonderful!