Why tube rectification?

In our opinion, done correctly, tube rectification sounds better in our designs to our ears.  In repairing components, we find that not using tubes was a short cut and cost savings.  Once done right, it can be glorious. All designers who use tube rectification in our opinion, again, does not make the sound that we achieve in our designs, Lamm included.  Not to say they sound not as good, but you have to hear the differences when compared to each other.

@whart - agree with your findings, but those units can be upgraded to achieve the sound you prefer.
 

Happy Listening.

if you end up taking tube rectification, you may find that rolling tubes offers a very clearly different character and weight of presentation. The manufacturer installed NOS AZ4 tube in my 4w +4w SET from Japan sounds fine, yet a contemporary production AZ4 mesh plate from EML gives much greater scale and dynamics, totally transforming performance of the amplifier, and EML seem to last notably longer than expected. Others have reported on this. YMMV.

I will add something that has not yet been mentioned explicitly.
 

What you are listening to from an amp/pre-amp is the power supply - not the signal being sent to it.

It is a bit of a misnomer that we call these things amplifiers. It implies that the signal itself is being amplified, and the other stuff is just there to help.

What is in fact happening is that the voltage from the power supply is being modulated by the input signal, and the input signal itself is swallowed by the tube/transistor. So what happens is the voltage from the power supply is either directed to ground or to the speaker, and the input signal simply regulates how much of that goes where.

This is why power supplies, especially in preamps and DACs, are so critical. You are literally listening to the sound of the rectifier after is has been smoothed out by some capacitors.

This +.

That is a good observation @joshua43214, yet, while I don’t doubt those who have said that changing rectifier tubes changes the sound, I do struggle a bit to understand why. After all if they are doing their job they should just be truning AC into inperfect DC, then the following caps, resistors and maybe inductors all smooth the DC. The real important thing about a power supply as I understand it is that it supplies clean and plentiful power. The audio signal doesn’t interact at all until the gainstage or preamp tubes and then again in the power tubes. So that is where desireable tube distortion or "tubiness" enters the picture. Now it is plausible that Rectifier tubes may introduce their own flavor of distortion into the power flow and that carries though to the final output. I can buy that and also accept that it might be desireable.

My own thinking on hifi these days is that music performance is to music reproduction as live viewing of a landscape is to an image of the landscape. Different expectations apply in each case and in the latter two intentional modification for effect is entirely permissible. That is, tone controls on an amp are just as permissible as impressionistic painting or jiggering the exposure of photos.