Why tube rectification?

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.

These two competing solutions both supply the basic power to the audio tubes and output transformers, so only indirectly interact with the sound signal. I have not read anything that explains what tube rectification brings to the party.

Voltage drop across the rectifier, especially when the amp is making power, is one very large reason rectifiers can affect the sound. The other reason is noise.

Solid state rectifiers are often blamed for making noise but its really how the power transformer interacts with the rectifiers. Between the two an electrical resonance can occur which is set into oscillation by the rectifiers turning on and off. The resonance might be at 2MHz but can cause the rectifiers and transformer to make noises much lower in frequency, which can leak into the signal chain and cause IMD. This is known as a 'swept resonance'. Its not something you often run into with a tube rectifier.

But it can be solved with proper application of snubber networks. The best approach is a small capacitance in series with a resistor across the input to the rectifier(s), directly across the output of the transformer.

Once the swept resonance is shut down there's no going back to tube rectifiers as the power supply sags less at higher power levels- which makes for less distortion at those power levels.

An obvious advantage of a solid state rectifier is the capacitances in the power supply can be quite a lot higher. There is often a fairly low limit to capacitor values when tubes are used. There are timing constants involved with these values. What you want is that none of the timing constants in the amplifier circuit be lower than those in the power supply- else the amp can much more easily modulate the power supply, resulting in higher distortion.

Tube if pared with a choke everyday. SS if no choke. 

Hello Bruce 19.  The reason to use tube rectifiers is that the high votage builds up slowly (versus instantly) and that avoids the schock of WHAM! all the capacitors in the unit are suddenly awakened from their fully discharged condition by the appliction of full power. This is particularly tough on the filter capacitors in the power supply. I once bought a used Adcom reciever at a very good price. I took it home and plugged it in and hit the power switch. A FLASH, a POW! and the room was FILLED WITH SMOKE. The unit had not been used in a looooong time. The electrolytic capacitors commonly used i power supplies are essentially a dead short when power is applied. The voltage causes a layer of bubbles to form inside the capacitor and that is the insulation between the "plates" of the capacitor. An old, perhaps physically dried out capacitor doesn't form the layer of bubbles quickly enough (if at all) to stop the flow of current through the capacitor. The bridge rectifier dumped all the current that could make it from the AC line, thru the fuse and into the essentially dead shorted capacitors. It takes time for a fuse to blow. Just enough time for the capacitors to explode, the solid state rectifier (diodes) to become cinders and the smoke to fill the room. Interestingly, the circuitry in the receiver never felt the operating voltage and was undamaged. I've got the power amp section running and the tuner section, but the line amp section is not working yet. It will, just as soon as I can find the time to fix it. Happy Listening.

In guitar amplifiers tube rectification is revered.  The class Fender and later Marshall amps all had tube rectifiers and the sound they produced is a touchstone for virtually every guitar amplifier since.  If you turn up the volume and strike hard on the strings the tube rectifier's relative slowness or sag acts as a compressor and gives a sound that's described as a cream like texture.  Mesa Boogie has offered a Dual Rectifier tube or silicon selectable line of amps for decades.