Can anyone give a simple, clear explanation of this, how it happens and so forth with an amp, and a couple well-known recorded examples? Thanks.
you mean with a valve rectifier?
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Quote by K33nbl4d3
I'll have to put the Classic T models on my to-try list. Shame the finish options there are Anachronism Gold, Nuclear Waste and Aged Clown, because in principle the plaintop is right up my alley.

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Presumably because the CCF (Combined Corksniffing Forces) of MLP and Gibson forums would rise up against them, plunging the land into war.

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Et tu, br00tz?
Happens with tubes rectifiers....

Large current draw happens when you hit a big chord. Puts stress on recto and it takes a split second longer than normal to deliver the voltage needed. This stress is heard as sag.

Kinda loose sounding. Hard to explain in words, sounds cool. Keeps the high end from being brittle.
^yep, it's really more of a feel thing... and you really hear it more on low notes, very apparent at high volumes and gain settings. There is a clip with a JTM45 which is tube rectified on my youtube channel, you might be able to hear it sagging a bit on the "How Many More Times" or "Whole Lotta Love" riffs, but I'm not sure if you can really tell from the clip, I kind of feel like the sag is a little less apparent with the el34s than it was with the kt66s but it's still there.
Ya should have mentioned that...you only get the sag at high volumes. At high levels the amp already draws more current then usual. Hitting big notes/chords then pushes the recto over the top.

And ya its the low stuff you hear the sag on...It does though take a bit of the high end out. I like it, nice and smooth.
It should also be noted that it gives high notes a blooming, singing quality. Great for blues or those leads that use sustaining high notes. Gives a very soulful kind of effect.