Why tube rectification?

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.

Hey Booerbillone Can't that problem be solved with a thermister in the path of the incoming AC mains line? I have only added them when called for by the designer but I don't think they would do any harm. Just slow the flow of AC while the thermistor gets up to temperature. No?

@onhwy61 You make the excellent point that tubes are sometimes beloved precisely because of the distortion they are capable of. Great example!

@atmasphere  there is no reason to have voltage sag at higher power with tube rectified equipment if the proper rectifier tubes are chosen.

there is no reason to have voltage sag at higher power with tube rectified equipment if the proper rectifier tubes are chosen.

@invalid Yes- I like the plural of the word as you chose, as that is what is needed. For example the Dyanco ST70 was designed with one rectifier tube when they really needed dual rectifiers. Because they cheaped out on this issue, the 5AR4 is more likely to fail than any other tube in the amp. You would need a number of tube rectifiers to really prevent sag. It is the Voltage sag which is why blues players in particular really like tube rectifiers in guitar amps.

IOW there really isn't a good reason to use them in a tube amp meant for home hifi use other than the nice glow. But the designer might not have figured out how to keep solid state rectifiers quiet so resorted to a tube rectifier instead. Tip: HEXFRED rectifiers are nice and quiet; so much so they often need no snubbing at all. They can handle high Voltage and currents that no tube rectifier used in the home can hope to match. So in a tube amp they can work quite well.