Swapping 5AR4 rectifier for 274B in a PrimaLuna Preamp

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:

http://www.300guitars.com/articles/rectifier-tube-voltage-drop-chart/

http://www.fourwater.com/files/fullrect.txt

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:

http://www.guitarplayer.com/miscellaneous/1139/all-about-rectifiers/16429

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 ;-) ].

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. ;-)