Preamp Rectifier Tube Confusion

@jjss49 I did! replacing the OEM 12AX7/12AU7 with Gold Lion. But I fell down the rectifier rabbit hole when I read about the Philips 5R4GYS. Ima sucker for aesthetics...the WE274B is sexy piece of glass! I figured if I can improve sonics AND have some cool looking glass then why not? 

Ima sucker for aesthetics...the WE274B is sexy piece of glass!

The two tubes have the same pin base with similar voltage limits and current specs, so you can interchange them and see how it goes. What is less obvious is the voltage drop you will see between the two- since the specs are very similar I suspect there will be only a minor difference between them.


You could also use a 5U4 which has the same pin base, but 5U4s have a greater voltage drop, and the 5AR4 was designed to have a controlled warmup time so as to allow the audio tubes (in particular, power tubes) time to warm up to prevent a phenomena called 'cathode stripping' which really does not occur with signal tubes as seen in a preamp circuit. The 5U4 warms up almost instantly. I've no experience with the WE tube. I'm saying that if looks are important, the ST-7 envelope used by the WE tube is also used by the 5U4. But I suspect you will find the 5U4 to sound a bit 'sleepy' due to the higher voltage drop across it, but they are so cheap you might get a pair and see what you think.

This is a quote from a recent review in TAS on the PrimaLuna EVO400 Preamp:

"To my mind, the 5AR4 tube rectifiers were at least partly responsible for the preamp’s tonal integrity, fleshing out the lower octaves and, in particular, infusing upright bass and cello with a full complement of tonal heft."

+1

"To my mind, the 5AR4 tube rectifiers were at least partly responsible for the preamp’s tonal integrity, fleshing out the lower octaves and, in particular, infusing upright bass and cello with a full complement of tonal heft."

That's a bit of a sketchy claim. Its far more likely that the audio circuit itself is responsible for this. A tube preamp can easily do exactly the same thing with solid state rectifiers (for example, by using 6SN7s in the line stage). Seriously, solid state rectifiers are now good enough that they easily keep up with tube rectifiers in terms of noise, but they don't have the voltage drop (which varies with current draw) that tube rectifiers do. Its for this latter reason that tube rectifiers are preferred in tube guitar amps, since that can impart that 'blues' sound which is really the sound of an amp that has a sagging power supply.


If you were to measure the voltage drop across the rectifier, you would find that the best sounding ones for hifi are also the ones that have the lowest voltage drop. There's nothing magical here- they respond to physics just like everything else in audio. And again- the power supply has to be working properly in that the filter caps are good and sufficient to properly bypass the supply and prevent noise from getting into the audio circuit. It that bit is true, then the only way a tube rectifier can affect the sound is by the voltage it puts out. So it should follow that if you use modern solid state rectifiers, you can make it even better, and in practice that turns out to be true as well.

Ralph... I think the world of you and have learned very much from you over the years.

I just posted what was written in the review.  However, I have sold, (as a dealer) and owned, (personally), quite a few preamps that have had tube rectified power supplies.  I have found without question, that I could change the sound by replacing the tube rectifier.  If this indeed due to a voltage increase or decrease, so be it, but it did and does change the sound.