Swapping 5AR4 rectifier for 274B in a PrimaLuna Preamp

Long time lurker, first time poster.
I have recently acquired a PrimaLuna Dialogue Three preamp.  (not the new 'premium' preamp, the original Dialogue Three)  It's a fantastic unit and sounds incredible.  I've achieved some very nice results tube rolling some of the other components I own(ed).  I am contemplating switching the OEM 5AR4 rectifiers with a pair of mesh plate 274B's from Sophia Electric.  
While allegedly pin compatible, I understand the life of the rectifier might run short.  To quote Sophia Electric's site:
"The 274B is direct heating tube. The indirect heating 5AR4 may turn on slower, however, people who buy 274B is for its superior sonic performance. To fully utilize its benefits, it may require first stage capacitor (capacitor input) to be less than 10MFD, or would shorten the 274B life span (very much like smoking is bad for your health). It would not be a problem with common choke input. Please consult to your amplifier maker or refer to a tube manual.
The maximum current capability for Sophia Electric 274B mesh plate tube is 90ma, suitable for tube pre-amp. "   

I was hooked on the SE 274B when I saw that Woo Audio was offering the 274B as an upgrade to their WA6 headphone amplifier.   Further research turned up a couple of great reviews for the tube in other amplifier and preamp applications.

PrimaLuna / Upscale Audio have given great recommendations for the Phillips 5R4GYS in my preamp.  In all probability I'll find myself buying & trying both and selling whatever comes in 2nd place.  

I'm pretty new to the tube game, but learning fast. 
I would welcome the opinions of those with more experience and finely tuned ears.  

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Have you ever tried the Mullard(Blackburn factory) GZ34(NOS, of course)? Long life and they deliver excellent sonics.
I replaced the stock rectifier tubes in both my Primaluna PL3 and PL8
with the Phillips 5R4GYS. I would say the improvement was significant.
I bought the Phillips from Upscale at the time for $40.00 Ea. They have since increased in price over time, and currently run $110.00 - $115.00 each. I liked the tube so well, I purchased NOS spares thru E-Bay for a considerable savings. There are a few international sellers that have them. There not hard to find internationally. Of course there are pros and cons of purchasing from Kevin and Internationally.  I was also recommended by rodmann99999 to try the GZ34. I search for quite some time before I gave it up. All I could ever find were sellers claiming there used tubes tested like new and I wasn't going to settle for anything other then new.  If you can find them (and can afford them) I would jump on the GZ34 Mullard (Blackburn factory) GZ34(NOS, of course). I had a Woo H/phone amp that the power supply used a B274 Mesh. There was a significance difference between the 274 and the Russian rec. tube supplied with the amp. Never used one in the Primaluna. I wasn't able to find enough info to satisfy me that they were usable with the Prima Equip. 
I included a couple of links below to Vendors on E-Bay selling Phillips Rec. Tubes. Also found a vendor from England that has several Blackburn NOS GZ34. Not a bad price considering the recent increase in value of the US dollar. You may want to get these, you don't see NOS Blackburn Mullards come up very offend now days.



Outstanding information!  Thank you very much!

Like t-bon3, I am new to the wonderful world of tubes and am also learning fast.


Regarding rectifier tubes, from what I’ve been able to piece together after significant research on the ‘net, is that the sonic differences between rectifiers is mostly caused by the “voltage drop” of each different tube model/design. This voltage drop is called “sag”. Apparently, under peek demands, some rectifiers will “sag” more than others, and this impacts how the rest of the amp performs with this brief drop in voltage from the rectifier tubes. From what I’ve found online, the 5AR4 / GZ34 family of tubes has the least amount of voltage drop, whereas the 5R4 family have the most (yet, many listeners prefer rectifiers with larger voltage drops – go figure):


Rectifier Tube Voltage Drop Chart:






From there, the story gets a little cloudy as to exactly what sonic differences are created between different rectifiers, and of course, how each one will perform in different circuit designs, with other pre and driver tubes, with your particular speakers, and your personal taste. Enter the ubiquitous “YMMV”.


I found a great article that describes the basics of how rectifiers work on the “Guitar Player” website:




Lastly, I’m not ashamed to admit, those “mesh plate” rectifiers like the Sophia 274B’s that t-bon3 mentioned (along with others), are darned seductive just to look at, and I’m considering installing a pair in my Cary SLI-80 just for their looks alone regardless of their impact on the sound [as I duck to avoid things being thrown in my direction ;-) ].



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Might want to also consider NOS Mullard or GE 5AR4s , use them in my Modwright & LineMagnetic gear. 
Sophia tubes have reliability problems and I would stay away if I were you. I've blown about 4 tubes in my life and they were all sophia. 
I phoned Upscale Audio and spoke to Kevin Deal. He made a compelling argument for the Phillips 5R4GYS, particularly in the Prima Luna Dialog preamp. I placed an order and should have a pair soon.

Thanks to all who responded - you gave me some great advice.
t-bon3,let us know how you like the Upscale Phillips 5R4GYS  tubes when you get a chance...

Can you please advise Kevin's technical reasoning for the above recommendation, i.e. why better specifically for the PL, and advantages / disadvantages over the Blackburn GZ34. I would be interested in learning the technology.
bradf - I am sure Kevin would be willing to explain his recommendation to you.

My 5R4GYS tubes arrived this weekend.   I swapped one channel so that I could compare the OEM PrimaLune 5AR4 tube on one channel to the 5R4GYS on the other.  I liked what I heard.  

I'm not a Audio journalist so my vocabulary is somewhat limited; however I can give you a concrete example of the difference the tube swap made.

A few weeks ago, I was listening to Sarah Mclachlan's "Surfacing" album - a 180gr Music on Vinyl release.  I wasn't satisfied with the separation I head on a few of the tracks.  It seemed like the vocals were lost in the instruments - the vocals should have stood clearly apart and airy against the music.

When I swapped tubes and listened to the same album and the same tracks - the "veil"  that I felt covered the vocals was gone.  I got the sense of space and separation that I was chasing.  

It was a pretty significant change, not subtle at all.  Even a neophyte audiophile like myself could hear the difference.

I can't say how they compare against something like the Mullard GZ34.

Hey t-bon3 – Thanks for replying to this thread with your experience in swapping out the 5AR4 with Upscale’s Phillips 5R4GYS. Interesting feedback, and is consistent with most other reviews I’ve read of the 5R4GYS.


What I find especially interesting, is that according to what I’ve found online, the 5R4GYS has more sag/voltage drop than the 5AR4, and yet many listeners prefer this higher amount of voltage drop. Logically, this seems counterintuitive. You’d think that a more consistent, and relatively higher, voltage level would provide a more powerful and stable power supply and therefore better overall sound. But, that does not seem to be popular opinion.


The Guitar Player article I provided the link to above seems to have the best “electrical” explanation for this. The writer is talking about guitar amps here, not hi-fi. But the explanation seems to make sense nonetheless:


  • From the article: “…The slightly compressed feel that a tube rectifier produces when hit hard can be a big part of the magic in some tube amps. It softens the front edge of the player’s pick attack while producing an enticing, explosive swell of notes just behind that attack, and can often make an amp feel more dynamic and touch-sensitive. Players and philosophical amp designers alike will also tell you that they sometimes hear more air and dimension in tube-rectified amps; a sort of bloom and spaciousness in the notes that gives them depth and texture.”


The only “logical” explanation I can think of, is that what listeners might be hearing when replacing their rectifier tubes is the “newness” of their newly installed rectifier tubes vs. their older, possibly worn-out ones that they replaced. It might be more a matter of tube age, usage, and wear-and-tear, and not inherent differences between different rectifier tubes.

In any event, the magic and mystery of listening to music through vacuum tubes continues. ;-)

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"Regarding rectifier tubes, from what I’ve been able to piece together after significant research on the ‘net, is that the sonic differences between rectifiers is mostly caused by the “voltage drop” of each different tube model/design. This voltage drop is called “sag”. Apparently, under peek demands, some rectifiers will “sag” more than others, and this impacts how the rest of the amp performs with this brief drop in voltage from the rectifier tubes. From what I’ve found online, the 5AR4 / GZ34 family of tubes has the least amount of voltage drop, whereas the 5R4 family have the most (yet, many listeners prefer rectifiers with larger voltage drops"

This has NOTHING to do with listening to home audio. The"sag" is what is happening when your’re hearing an electric guitar amp being overdriven, producing the tones of some guitar gods.

I trust my ears.  I'm only on my second tube pre-amp, but I'm learning fast.

My first was a Chinese made "mid-grade" pre-amp that benefited immeasurably from being re-tubed with quality parts.  The rectifier tube upgrade made the most significant improvement.  That was a 5Z3P --> 274B swap.  

The starting point on the PrimaLuna Dialogue, my second tube pre-amp, was already pretty high - so one has to work that much harder to squeeze out a performance improvement.  Since Upscale is the US Importer (i believe) for PrimaLuna, I had to trust his tube recommendation based on his extensive professional experience with them.

Getting back to "trusting your ears" - I had a particular album, with particular tracks that just weren't right.  Swapping the tubes and playing the same track convinced me.  Sagging voltages and other electrical engineering topics are way over my head.  I stopped at "sounds better to me"  :-)   I wish I knew more about the science behind the sound.  

....what I really wish for was more time to sit back and RELAX with good music.
Thank You, t-bon 3.
I really don't like to bother Kevin with theoretical questions unless I have intent or potential of purchasing the relevant  item. He's pretty busy trying to put food on the table. After all, he is a retailer, not the shell answer man. I usually try to make best of this forum, just like you did when I took the time to answer your questions.

Just installed two of the Phillips 5R4GYS rectifier tubes into my PrimaLuna DiaLogue Premium preamp. With only a few hours of break in time.. I would consider these a must have tube for this preamp. Right off the bat, the increase in sound quality is huge. The impression of a more natural tone to instruments and voice is just plain awesome. The emotion and feel across the board is something to behold. And all this from a brand new,unused...non broken in pair. WOW!

The music now has meat on the bones and a true quiet elegance to the sound that was hugely lacking with the stock PL 5AR4 version. The review from Positive Feedback is spot on and true to this NOS tubes virtues... If you can...get a pair ASAP,before they are g-o-n-e. I am very happy I took the plunge. Hearing is believing.
Installed six-matched NOS Mullard 12AU7 CV4003's into the PL Premium preamp. These NOS Mullard tubes in tandem with the Phillips 5R4GYS is just plain crazy good and outstanging in every way to the service of the music.. I no longer have a  PrimaLuna DiaLogue Premium pre amp...nope...no sir ree Bob!!! ...It is now a 'Super' Premium pre amp in every way that matters most to the music played through it.   ; ^)