[Arny Krueger]

"Iain Churches" wrote in message
.fi
"Arny Krueger" wrote in message
. ..
"Eeyore" wrote
in message
Iain Churches wrote:

But then SET amps traditionally
have little or no NFB and so are inherently stable

An absence of NFB **DOES NOT** make any ampliifer
'inherently stable'. Such an idea is pure horse manure.

Right. Now if Iain said:

"But then SET amps traditionally
have little or no NFB and so are inherently resistant to instability due to
NFB", he would have an obvious truism, but at least he would be right.

Obviously, an amp can become unstable for reasons other thanpoor design of
the NFB.


Yep, in fact NFB that is truely NFB never causes
instability. Instability only comes when a loop that is
NFB in the mid band becomes positive feedback due to
phase shift, usually at the frequency extremes.

Good. Things are getting better round here. Arny has made
a statement on topic:-) The FB that may be negative at
say 1kHz may well swing through positive at say 120kHz.

A tube amp without feedback is, by definition, not prone
to such problems.

Similar symptom, different cause.