Adventures with the RCA 5670 and WE 396A Vacuum Tubes

Now, I would like to start to share with you my experiences on the sound quality improvements of “Douk Audio U4” itself.

The first thing I wanted to say is that as soon as I started listening to this mini USB DAC more than two years ago, I felt that the Russian tube that came with the component was not able to bring out even half of the potential of the “Douk Audio U4”.

I heard the sound as passably dynamic with some sharpness, but the musical expression was bland without any richness.

So I looked for compatible tubes and fortunately came across two vintage tubes such as RCA 5670 and WE 396A. These NOS tubes were produced in early 60’s or 70’s.

In my article, “Alan-san’s PX25A monaural SET, Part 5”, I announced that we would have a listening comparison between RCA 5670 and WE 396A.

These interesting listening sessions were conducted almost simultaneously on both coasts of Pacific Ocean with my friends in the USA, Alan-san and Honda-san, and also Japanese kindred spirits, Kajiwara-san, Nishikawa-san, and myself from the end of 2022 to early 2023. 

Needless to say, RCA was a famous manufacturer of vacuum tubes for consumer use, and Western Electric's vacuum tubes boasted extremely high reliability and were mainly used for business and military applications.

Well, I was so much moved by the enjoyable sound RCA 5679. The sound was generally bright with exciting dynamism. In addition, the tone was also attractive, and it reminded me of the beautiful tone, played by Altec Corona plus JBL2405 in Alan-san's system.

In particular, the bright and gorgeous tone of the early 1960s RCA 5670 enriches the listener's heart, so if the overall tone of your system is a little dark and warm, this 5670 will be able to contribute to a more appealing sound.

On the other hand, WE 3960A's sound was natural, rich, and full of musical energy. The tone was mature, and I couldn’t help but feel the highest quality musical balance and also solid framework.

If anything, I felt that WE 3960A was totally winning in the richness of deep musical expression. Although the WE 396A was a miniature tube, it was so strange that it reflected the fame of Western Electric tube’s sound character.

Anyways, we - all of us - were very lucky to be able to experience those wonderful vintage mini tubes, made in the 1960s and 1970s, more than a half century ago.

Let me share with you Alan-san’s impression: “Anyway, I find this WE 396A to sound absolutely marvelous! Like yourself, I was pleasantly pleased with the natural sound and timbre, presenting an addictive and stunning performance. But, I feel the RCA 5670 is more dynamic, energetic and forward sounding. I like your description of it being “glossy.” Thank you Yazaki-san for the kind introduction to the vintage RCA 5670 and WE 396A tubes!” 

Well, I looked for the origin of these tubes, and found that both tubes, the RCA 5670 and the WE 396A, were designed for RF applications operating to VHF/UHF, which were designed with a rugged structure that was needed for the lowest microphonic noise.

I’m now convinced that the minimal microphonic noise was a big factor in the clear, transparent sound that made it possible for us to hear every minute sound and subtle timbre shading common to these two vacuum tubes.

Of course, we would like to pay tribute to the excellent circuitry and mechanical design of this mini USB DAC, the Douk Audio U4. It can clearly express the differences in the sound of these significant tubes, and above all, its reasonable and affordable price. I think the U4 is really an excellent example of the digital audio age, one which has leveraged well the monumental analog assets of the past.

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