"Stewart Pinkerton" wrote in message
...
: On Tue, 28 Mar 2006 08:59:43 GMT, Patrick Turner
: wrote:
:
:
:
: Arny Krueger wrote:
:
: "Patrick Turner" wrote in message
:
:
: They are only as linear as a triode with regard to
: voltage gain when external loops of NFB have been applied,
: as in the case of the emitter follower connection or
: having a few BJTs with a loop of NFB around the
: lot of them to correct all their mistakes.
:
: BJTs are inherently non linear for voltage gain and MUST
: rely on large amounts of externally connected loops of
: NFB.
:
: Simply not true. Local feedback works well with BJTs.
:
: Local loops are externally applied loops of NFB.
:
: Bjts are so damned non linear with regard to voltage gain that large amount of
: NFB, local or otherwises must be applied
: to linearize the outcome, as well as raise input impedance.
:
: Some BJTs are more linear than say a 300B. Why do you keep ignoring
: this *fact*. Heresy?
:
: It isn't ludicous to drag people screaming back to the basics.
: The basic fact is that bjts WITHOUT ANY NFB, LOCAL OR OTHERWISE applied
anywhere
: have hopelessly poor
: voltage gain linearity.
:
: Utter bunk, check the spec sheet for the 2SA1216. Gain linearity is
: flat as a pancake at elevated junction temperatures, as would be
: experienced in a Class A amplifier.
yep, checking, i found it he
http://users.otenet.gr/~athsam/database.htm
the third graph shows Vbe - Ic, the _run hot_ curve
does 0.8 V Vbe @ 6 A, 400 mVtt giving 6 Att with 1.6 % distortion
certainly impressive. but, now realize the curves are taken at a
constant Vce=4V - not very realistic, is it ?
now, Hfe about 100, at this 24W class A idle point,
60 mA of base current is required. oops, at 10 A, Hfe has
gone south to only 60, creating an additional few dozens
of THD %.
2nd take:
0.6Vbe, 2.2 A idle now Hfe stays flat with 200 mVtt in, 4Att out,
distortion is 7 % or so that's indeed quite an achievement
but considering it's taken at constant Vce
reality will be worse
: Statements have been made on the group that what i am saying is untrue.
:
: That's because it is - see above.
hm, about 12 W / 8 Ohm available, 7 % THD, 8.8 W idle with the 2SA1216
you're saying there are no tubes that can beat that ?
hmmm
the truth,
Rudy
: --
:
: Stewart Pinkerton | Music is Art - Audio is Engineering
:
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