Oct 172018

In a special mid-week treat for you, it is with great delight that I welcome back Shirokazu Yazaki to the pages of Jeff’s Place to tell us about his latest adventure in Real Sound with his good friend Alan-san!

Yazaki-san (center) with friends in Tokyo.

Welcome back Yazaki-san, and thank you for sharing your latest adventure in Real Sound with us – I loved reading about yours and Alan-san’s adventures!

¸¸.•*¨*•♫♪ ¸¸.•*¨*•♫♪ ¸¸.•*¨*•♫♪

Adventures in Real Sound: Alan-san’s GEC PX25A (DA30) Monaural Single Ended Triode (SET) Amplifiers!

One day in early April in 2016, Alan-san, my best audio friend and also a very eager reader of Jeff’s Place, and I exchanged emails, which led to the start of building up his PX25A mono SET, but it was really a long adventure not only for me, but also for Alan-san, who had waited so long time patiently for the completion of the SET.

Shirokazu: “Recently I have been asked to modify or build up several tube amplifiers, one was the restoration and the modification of Handoko-san’s Marantz Model 7. Handoko-san lives in Indonesia. The other was Harald-san’s request for me to build up a WE310A-DA30 mono SET, just the same as Ookubo-san’s “Altec Green” painted amplifier. Harald-san lives in Switzerland, and was eager to proceed.”

Yazaki-san’s vintage Marantz 7k preamplifier.

DA30 SET monaural amplifier.

Alan-san: “Very good to hear about your ongoing amplifier adventures, they will be very good machines, those two are very lucky people. I was very intrigued when reading about Ookubo-san’s WE310A-DA30 SET. If after finishing building up these two projects and you still have the desire to continue, can I sign up for commission number 3? Please know that this does not require an answer at this point, I was unaware that you were able to build up another “Altec Green.” Please understand that I do not mean to impose on our friendship, so if this is not possible, it is absolutely positively fine.”

Shirokazu: “I personally appreciate your interest in my WE310A-DA30 non-feedback SET amplifier. Surely, I have long felt something healing about the sound of the DA30 SET with the finest and very rich tone. The driver tube, Western Electric 310A, oldest mesh shield, too rare to get would be the best driver tube ever made and also DA30 / PX25A, vintage direct heated power triode, made in England would be something gem, so rare to find out at present, has loftier and more beautiful timbre compared to famous WE300B, I have experienced.”

“And so the amplifier would bring out not only American traditional gorgeous sound of WE310A but also the best virtue of the British made DA30. I believe this SET could offer you this gorgeous sound, with no compromises. The most difficult things for building up the amplifiers would be finding the high-quality output transformer and the very rare vintage vacuum tubes, including the best quality rectifier tubes. Anyways, when I came across the output transformer, the primary impedance 5 k ohm for SET, I could accept your very polite offer. But for your future adventure, you also had better to search for some high efficiency speaker system in a good condition.”

Vintage Altec 832A Corona loudspeakers. Photo by LA Jazz Audio.

About the high efficiency speaker, we immediately started our search. Fortunately, after 3 months of looking, one summer day we came across a pair of vintage Altec 832A Corona loudspeakers in really mint condition, and of course, Alan-san bought them.

Curiously enough, it was surely a coincidence, but I knew from Jeff’s Place that Jeff-san also had just got the same type and color of Altec 832A at the same vintage audio shop in LA in early February in 2018.

Vintage Altec 832A Corona domestic loudspeakers in my main listening room.

(That was an amazing coincidence! By the way, LA Jazz Audio was great to deal with, their shipping was done expertly, and the Altec 832A Corona loudspeakers I bought from them are amazingly musical and beautiful loudspeakers that are somewhat rare these days in the world of Altec vintage loudspeakers. Hint: There’s a beautiful mahogany pair for sale right now on eBay by LA Jazz Audio. It may be your only chance ever to get a mint pair of vintage Corona’s. If I had the extra $ right now I’d buy them myself so I could have Altec’s in every room in my home! – Jeff)

Well, our first adventure of Alan-san’s PX25A (DA30) mono SET, longing and searching for the very best vintage tubes and best suited transformers begun in just this way.

Contribution of “Jean Hiraga-san” to Our Japanese Tube Audio Scene

But now, I’d like to recall to my younger days of early 70’s. When I come into TEAC as a mechanical engineer in 1971, I remember well that Jean Hiraga-san started importer business of dealing with especially European tubes at Kobe in Japan, named “Sansei Enterprise”. For publicity, he offered his imported tubes to the main writers of “MJ”: Asano-san, Morikawa-san, and as I mentioned before, Anzai-san. And so from 1971 or 72, we often saw the articles about them making their own tube amplifiers in every monthly issue of “MJ”.

At that time, the WE300B was already well known among tube enthusiasts as the best triode, but no one knew the name of DA30 (PX25A), PX25.

The PX4, a made in England vintage tube, which Hiraga-san first imported, made Jean Hiraga-san highly influential in the Japanese tube audio scene. Of course, I was so excited to read about such articles on “MJ” and I was really intrigued mostly by the powerful DA30 vacuum tube. Its heater voltage and current was 4V / 2A and 8 W, being bigger than the WE300B at 5V / 1.2A and 6 W, and so we could look to it for more final power. Furthermore, I adored the well-proportioned shape of new dome type of DA30 at one glance, something modern and beautiful. Also, its price of JPY 4,840 was attractive for me as at that price I could succeed in getting a pair for my monthly salary. 

Master Anzai-san’s GEC PX25A Single-Ended Tube Amplifier

The DA30 has one negative point, as to make full use of the true potential of DA30 it needs remarkably high voltage to drive the DA30. A lot of types of circuitry trials, such as using inter-stage transformer between the driver tube and DA30, or power-drive by an EL34 were made public in “MJ” by a lot of well-known writers in almost every issue.

At last, I came across an article by Master Katsutaroh Anzai, using the WE310A to drive the PX25A in a stereo amplifier in the July issue of “MJ” in 1972. I was strongly impressed with his very beautiful circuit with the simplest design, and also his extraordinary passion for and commitment to the WE310A and DA30.

From his articles, I understood well the forceful driving power of WE310A. He managed to bring out over 100 output voltages under the condition of 40 dB gain from the WE310A with his careful study. Also, Anzai-san showed the real frequency characteristic of the WE310A’s output voltage in his articles, so it was very clear about the true potential of its dynamic range and outstanding linearity.

Anzai-san affirmed for us that there might be nothing else like the WE310A, the most powerful driver tube ever made. Really, the heater voltage and current of WE310A are 10 V / 0.32 ampere, and so only from the view point of consumption of heater wattage, 3.2 watt, WE310A would be regarded as a pretty powerful tube. I had some concerns about what the WE310A might sound like, because it was a pentode and not triode.

In my understanding  that the pentode is noted for its higher gain, but on the other hand, its negative factors are the higher internal resistance compared to the triode, and also its tendency to generate harsh odd-numbered harmonic distortion.

I got a hint from Anzai-san’s article about the splendid high range characteristic of the DA30, with the new dome type. For example, the frequency response of WE310A at 20 kHz was -2 dB, and the frequency characteristic of his amplifier’s output was just the same value, -2 dB / 20 kHz. It means, despite of WE310A’s high output impedance, DA30 didn’t have any transmission losses in high-range from the signal level of the WE310A, and that’s without the help of a negative feedback circuit.

These facts would be the true evidence of the DA30’s significant superiority to the WE300B or any other direct heated power triodes, I suppose. 

Well, you might know well the name of Western Electric 91B amplifier, this amplifier, composed of WE274A and WE310A-WE310A-WE300B would be not only a historic vintage amplifier but also it has been regarded as the best single-ended tube amplifier, ever made for some enthusiasts.

In Japan, from the early 70’s, a lot of WE91 type amplifiers, composed of the WE310A and WE300B, and designed with non-feedback circuitry, have been seen in many articles in specialist magazines.

It was common for those kind of WE91 type SET amplifiers that the frequency characteristic declines from -4 dB to -6 dB at 20 kHz. I saw this declination starting from around 5 kHz.

I had thought then, and think so now, that the minimum requirement for the width of frequency response of 20 Hz to 20 kHz is very critical for modern “High-Fidelity” reproduction, so I didn’t accept WE91 type design with the non-feedback circuits.

But why the DA30, especially the new dome type that has such a remarkable characteristic of high range? Are there any reasons?

Yes, the new dome type DA30 has quadrupole construction, which could surely reduce the stray capacitance of each other’s electrical poles, plate, grid and cathode.

I heard that this improvement of high-frequency range of the DA30 had been done in the midst of World War II, and I have no other choice but to recall the historical fact that it was said that England was saved from the invasion of Luftwaffe by the radar arrays on the white cliffs of the Straits of Dover.

Now we can find out that such a leading-edge telecommunications technology in Great Britain more than 70 years ago was made possible by this new dome type DA30 vacuum tube.

The old balloon type of DA30 is a genuine direct-heated triode with a rich low range, but I have felt some darkness in its timbre and a shortage of high-frequencies in this rare power triode.

Of course, it must be come from my personal hearing sense, but I far prefer the new dome type rather than the old type. At the same time, I have known well and comprehended that almost all of the elder writers said the old balloon type of DA30 had deeper sound & timbre, and they liked it.

Anyways, I successfully completed the building up of the DA30 SET without any negative feedback circuit, according to Anzai-san’s design from early February in 1973.

It has been a very huge blessing for me that I have fully enjoyed the sound of the combination of this SET (with continuous modifications over the years),  and my Altec loudspeakers with Onken mid-driver, new 500MT + tweeter, 5000T Esprit, throughout the more than 40 years I have owned it.

I’d like to add one more thing about the superiority of its output transformer, old TANGO FW-50-5S with its big size EI core, that Anzai-san first introduced in his article.

To tell the truth, I haven’t wanted to change my DA30 SET to another type of power amplifier, such as high performance push-pull tube amplifiers with deep negative feedback and their inevitable phase correction, because my very sensitive Onken horn system with 105 dB / W sensitivity could express lucidly every kind of minute artificial “makeup” of its skillful circuitry, I have felt.

There might be another reason too, that being the forceful back electromotive force generated from powerful magnetic circuit with huge Alnico magnet and super lightweight diaphragm, could be far bigger than the usual driver, and have much effect on the amplifier.

Yes, the DA30 SET with no negative feedback circuit doesn’t experience these harmful effects.  I firmly believe, if you want to hear really organic vocals or truly “Real-Sound”, a well and simply built SET that is equipped with fine tubes and a well-suited output transformer, would be the right choice, but of course, you would need to use a high-efficiency speaker like the Altec’s.

Yes, you had better be prepared not to use modern low-efficiency speakers, but hopefully you can find a vintage Altec high efficiency horn speaker system. Such a system could bring out not only nuance-filled vocals, but also you could find out the real and truly stereophonic acoustic guitar sound with sparkling timbre of each string. Once again, I’d like to say, these sounds reproduced through such an SET and the high efficiency speaker would offer you another dimension of live-like feelings from the music.

Well, I imagine, such a system might be exactly what Alan-san has long searched for to his audio life and I only hope, Alan-san’s new GEC PX25A mono SET would have the potential to realize his vision. Alan-san loves music and enjoys playing blues guitar with a vintage tone.

I think there would be a lot of readers of Jeff’s Place who have patiently persevered in their long adventure in pursuing “Real-Sound” just like Alan-san and I have, and so I’d like to share with you the details of Alan-san’s GEC PX25A mono SET in my next articles, the way I actually experienced it.

I’d like to add a postscript that you could see what Mr. Jean Hiraga is up to lately on these web-sites HERE and HERE, which my young friend, Nattawut-san, at the Sentimental Café in Bangkok has informed me of. Thank you so much, Nattawut-san!

Also, I just come upon my master, Anzai-san at Tube Audio Show 2018 in Tokyo, on Oct. 8th. I was so delighted to see him, and to know that he is alive and well.

Well, they are true seniors for me, having introduced me to such a deep and rich world of audio adventure. Thank you very much, Mr. Jean Hiraga and Mr. Katsutaroh Anzai with my heartfelt respect!

¸¸.•*¨*•♫♪ ¸¸.•*¨*•♫♪ ¸¸.•*¨*•♫♪

Many thanks to Yazaki-san and Alan-san for sharing their most excellent adventure with their DA30 / PX25 SET monaural amplifiers, and I can’t wait to read the next installment about their adventures!

As always, thanks for stopping by, and may the tone be with you!

 Posted by at 11:04 am

  10 Responses to “Adventures in Real Sound with Yazaki-san: Alan-san’s GEC PX25 monaural SET’s!”

  1. Hi Jeff,

    The PX25 is such a great sounding tube!!!!!


    • It sure is, Pete.

      One of my favorite amps that I’ve heard was Stephaen’s Art Audio PX25 that he had ages ago.

      Kind regards,


  2. As my auntie was fond to say, “Try it, I like it!!”


  3. I am so very grateful to you both, Yazaki-san and Jeff-San, thank you very much!!

    Warmest Regards,

    • Thank you, Alan, appreciated!

      I’m looking forward to seeing some photos of your system in an upcoming article!

      Kind regards,


  4. Dear Sir,

    I am looking to built a new SET amplifier and I hesitate between 300B (Takatsuki ) or PX25 (Osram) output tube.

    I really hesitate between this two tubes for the best tone on 99dB speaker, not really loud, on jazz and classical (John Williams, Rachmaninov..).

    Can you advice me ?

    Thank you 🙂

    • Hi Julien,

      I don’t have a good answer for you, but perhaps Yazaki-san will see your message and be able to answer your question.

      Kind regards,


    • Dear Julien-san,

      You are so lucky that you have an envious dilemma for selecting
      300B or PX25. These are the best triodes ever made that you might
      not feel any regrets whichever you choose, I suppose.

      But you might have known well that PX25 and PX25A / DA30
      are each another type of power triode.

      Well, I think the circuitly, the first tube and the driver tube are
      also very important. If you had any questions, please feel free to
      contact me. I hope I could give you some advices.


      Regards, Shirokazu Yazaki From Tokyo

  5. I believe it should be pointed out that the PX25 and the PX25A are quite different tubes.

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