[Arny Krueger]

wrote in message
ups.com...

What's interesting (e.g. yet another tangent road I'd like to travel
down further) is that traditional tube designs, or so I hear, don't use
feedback,

False. Feedback has been part of tubed amplifier designs going back to the
1930s.

but to design a transistor-based method without feedback
would be dangerous (unstable).

False, sort of.

Audio amplfiers are actually designed in two domains - AC and DC. The DC
design of an audio has traditionally related to stabilizing operating points
for the active components. The AC design relates of course to how the
amplifier amplifies audio. In some cases the AC and DC designs converge and
the amplfier operates the same at all frequencies including zero frequency
or DC.

If you don't stabilize the operating points of either a tubed or SS circuit
it will be prone to either drift to a high distortion operating point, or
drift to saturation and perhaps overheat, or drift to cutoff and not amplify
at all.