Aug 272017

I wrote all day yesterday and finished up the review of the Sophia Electric EL34-ST and Aqua 274B vacuum tubes.

The Sophia Electric EL34-ST power tubes (above) and Aqua 274B rectifiers (below) outperformed everything that’s ever graced my Leben CS-600 integrated amplifier, and vintage McIntosh MC30 monaural amplifiers, respectively, and by a large margin.

I don’t know what makes these tubes sound so magnificent musically and sonically. I could be the contribution of the ST bottle shape, or the noise reducing blue glass, the design & materials of their internal structure, or Richard’s prowess in voicing tubes, but the Sophia Electric Aqua 274B rectifiers and the Sophia Electric EL34-ST power tubes are both home runs by Richard, and they are simply superb both musically and sonically.

Your can read the full review here.

 Posted by at 11:00 am

  12 Responses to “The Sophia Electric EL34-ST and Aqua 274B Vacuum Tubes Review is Now Live at Positive Feedback!”

  1. I am looking for 2 quads of el34s. How do these Sophia EL 34ST compare to the NOS Mullard XF2 EL 34s? Do you have an idea?

    • Hi Dan,

      I don’t know how they compare. If you decide to get the Mullard’s let me know how you like them. Brent Jesse has an interesting discussion about the Mullard XF2 EL34’s with both single and dual halo getters here.

      All the best,


  2. Hi Jeff, I read your Sophia Electric Aqua EL34-ST tube review with much interest thank you.
    I’m slightly confused though and am hoping you can help.
    I own a Leben (rs28cx pre and) cs660p power amplifier using 4 Russian NOS 6n3cE tubes and am interested in upgrading the cs660p by changing to the Sophia Elec Aqua EL34-ST tubes.
    My questions are
    1/ how many EL34-ST tubes do I need to buy for my cs660p and
    2/ should I also consider the 274B rectifier tube? (I’m not sure what these do or where they fit) and if so how many do I need?
    3/ now that some more listening time has elapsed, in your opinion is the above worthwhile?
    Kind regards,

    • Hi Stuart,

      The Sophia Electric Aqua EL34-ST tubes should work very well as power tubes in your Leben CS660P, much the same as they did in my CS600. You would need four EL34-ST power tubes for your CS660P.

      You’ll also need to set the switch settings appropriately for the CS660P when using the EL34’s, and using EL34’s will reduce the power output of your CS660P somewhat.

      The SE 274B tubes will not work in your Leben CS660P, as it uses a different method of rectification.

      If you decide to give the Sophia EL34-ST’s a try, be sure to report back and let me know how you like them in your CS660P!

      All the best,


  3. Hi Jeff;
    can I just replace the Sophia blue 274B against my 5U4G`s without changing anything in my MC30`s as well as the
    newly announced 5AW4 tubes?
    I would really give it a try.
    All the best and a merry Christma time.

    • Hi Claus,

      The Sophia 274B Aqua can be used just like the 5U4G and 5AR4 rectifiers, where the first capacitor in the power supply after the rectifier tube can be up to 47uF.

      The nice old NOS Tung Sol 5AW4 rectifiers have really nice tone, but they can’t match the Sophia 274B Aqua in overall performance in terms of transparency, spaciousness, etc., but I still urge you to give them a try if you can find a set.

      While the 5AW4’s can’t quite go toe-to-toe with the Sophia’s performance wise, the Tung Sol’s are the second best rectifier I have tried, and at $8 USD each they’re an incredible undiscovered bargain

      Let me know your impressions when you give them a try!

      Kind regards,


  4. Jeff,
    thank you very much for your message; If you say yes, I guess I`ll give the `Aquas“ a try. Have you ever tried 5r4GY`s?
    I use them for years now instead of 5U4G´s and they perform extremely smooth; right now I am using wonderful old Brimar /CV717 but I guess that`s not the top of the cake.
    Could you give me a recommendation on your favourite tube setup in your MC30`s ?
    would be really nice as well as the tubes for the MX110; I am using both,just like you but with different kind of JBL 43xx studio monitors.
    kindest regards

    • Hi Claus,

      I haven’t tried the 5r4GY’s that I remember, but thanks for mentioning them, I’ll check into them if I get the chance.

      The Aqua’s are very nice rectifiers. They are smooth, extended, and transparent, and are very nice tonally.

      I really like the tone of the NOS Tung Sol 5AW4 rectifiers. They don’t sound as extended and transparent as the Aqua 274B’s, in fact they sound a little rolled off, and are more midrange centric in their presentation, but they are really nice in that they seem to reduce noise in the presence region, make for a very nice presentation.

      Which rectifier will be best in a given system will depend on the system and tastes of the owner, but it’s hard to go wrong with either one.

      I’ll have to check on the tube complement on my MC30s and MX110Z and get back with you.

      Kind regards,


  5. Hi Jeff;
    thank you very much for your remarks.
    If you get your hands on a nicely matched pair of “ugly” mushroom RAYTHEON Jan 5R4WGB`s , try them. The 5R4G family is
    underestimated. The mentioned Raytheons should be cheap ans easy to get in the U.S.
    would be interesting to hear your impressions.
    I am just planning giving my MX110 to my Mc technician and I was very interested to read your upgrades with the Arizona
    Would you give me support for the MX110 upgrade by telling me what parts I need that make a real improvement?
    kind regards

    • Hi Claus,

      I’ll look around for a pair of the Raytheon’s, thanks for the recommendation.

      For the MX110, I ended up removing all of the modifications related to the Arizona caps, and the metal film resistors.

      Mastering engineer, Steve Hoffman, once told me he has never heard modifications to the MX110Z that improved upon its overall performance, and I’m inclined to largely agree with that.

      The only modification to the MX110Z that has stood the test of time for me is replacing the cathode follower caps with the prototype 0.22uF Duelund CAST tinned-copper caps that I talked about here.

      Unfortunately, the production version of the 0.22uF Duelund CAST tinned-copper caps will not fit within the available space of the MX110 as their diameter is too large, as my friend George and I found out recently after he ordered a pair to modify his MX110 with.

      I’ll check into Frederick to see if there is a solution to this issue, but in the meantime I would recommend you leave your MX110 as is.

      Kind regards,


  6. Dear Jeff,
    thank you so much for your comments and recommendations; time to send you a big Thank you for your great and outstanding blog that encourages many of us that much.

    As for the 0.22uF Duelund CAST tinned copper caps: I would be more than pleased if you kept me posted when they are available and if Frederick has a solution to get the size problem fixed. As well I would like to know if they could ordered directely from him, when available or maybe from you.
    I am anxious to hear news, Jeff.
    kindest regards

    • Hi Claus,

      I just measured the prototype 0.22uF Duelund CAST tinned-copper capacitors with my caliper, and the diameter is 26.46mm and the length is 62.72mm.

      On the Parts ConneXion web page it says the Duelund 0.22uF JAM tinned-copper capacitors are 25mm diameter and 55mm in length, which means they will fit in the MZ110 with no problem. The JAM caps are also much more affordable at $46.8 USD each.

      I have never heard the JAM caps, but if they are anything like the CAST tinned-copper prototypes they should be very impressive.

      You can reach Frederik at should you desire to ask him about some custom CAST capacitors for your MX110.

      All the best,


 Leave a Reply

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>



%d bloggers like this: