"Patrick Turner" wrote in message

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.

External to the device, but not external to the stage of amplification.

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.

So what? In the end BJTs can be, with a trivial amount of effort, be used to
make the most linear amplifiers known to man.

This applies regardless of whether you build a preamp
with an opamp, a discrete transistor preamp,
or any power amp.

Triodes don't, they have a small amount of NFB built
into them.

Compared to BJTs, triodes have massive amounts of local
NFB built into them, and they are often used with
addtiional local and/or loop NFB.

You don't know how much NFB is within any given triode
now do you?

In the case of triode-connected pentodes, the amount of NFB is exactly
knowable. Just reconnect as a pentode.

But it doesn't matter because nobody in their right mind who is out to
design the lowest distortion amp around is going to use tubes.

Please provide some calculations and details to prove to
the group that you have the slightest idea about what you
are talking about.

Asked and answered.

Keep your answer to less than 5,000 words.

Been there, done that.

I would ask Trevor to set up a simple 1 transistor
preamp with a BC109, and without any
NFB applied, not even an emitter current feedback
resistor, and as a common emitter voltage amplifier with
a supply of 20V.

An apples-to-apples comparison would involve comparing
circuits with gain and impedances, both input and
output, that are as typical and similar as possible.
However, this comparison is totally ludicrous, because
nobody in their right mind uses a stand-alone BC109 as a
high grade audio amplifier any more. They'll use some
kind of an op amp, perhaps a NE 5532 or its equivalent.

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.

It doesn't seem to matter, does it. In fact the lowest distortion amps
around are SS, not tubes. In fact every modern recording console of
substance is based on SS. Every modern music player is based on SS.

Statements have been made on the group that what i am
saying is untrue.

I've mostly said the truth about your statements, Patrick: They are
irrelevant.

All opamps also must be used with NFB, and they contain
many interconnected bjts like many
discrete component amplifier, so the non linearity of all
these adds together and must be linearized with NFB.
opamps usually have way too much gain without NFB; and
usually poor open loop bandwidth,
something also flattened out by NFB.

So what? There is no such thing as a tubed amplifier that is even 1/10 as
linear as a $0.25 op amp, as said op amp is typically used.

To understand his own utter stupidity, I ask Trevor to
also set up a 6SN7 with a 250V supply to act as a preamp
and without any loop NFB, and he can then tell us all
about the results which will prove what a
jackarse he is.

Illogical comparison. Everybody knows that 6SN7s have a
ton of internal feedback, and that BJTs compare most
closely to pentodes, not triodes.

A "ton" of NFB is an extremely uninformative unit applied
to NFB.

OK, its more like 1,000 KG. ;-)

Please try be specific and factual lest we consider you
to be utterly stupid like Trevor.

Exactly how much NFB is within a 6SN7?

It's not practically knowable, and its irrelevant on the best day of its
life.

I will also say that a 6AU6 pentode would be more linear
at a volt of output than a BC109 at a volt of output,
with both devices tested without NFB of any kind.

Say what you will Patrick. Your challenge is finding anybody with a brain
who cares.

Unless you have done the experiments and comparisons, you
remain uneducated about the basics.

The facts are before us. Nobody in their right mind who wants the most
linear amplifier uses tubes. Tubed amplifiers are mostly used in the 21st
century as EFX boxes.

When people talk about the linearity of devices, what is
being stated is the linearity of the devices without
any external loops of NFB applied. That is what engineers
understand when somebody talks of device linearity.

It doesn't matter. Consumers don't care what the parts inside a box do, they
care about what the box does.

bjts offer fair current linearity between base current
and collector current but offer hopeless
voltage linearity.

So, use feedback to linearize them. Where's the beef?

Amplifiers are built to provide voltage linearity
regardless of current variations due to load variations.

Thanks for agreeing with my claim that consumers don't care what the parts
inside a box do, they care about what the box does.


External loops in circuit applications of NFB are never
included in discussions defining device linearity.

So what?

You cannot say a bjt is linear if you are using an
emitter follower as an example of the device use.
The term "emitter follower" is a description of a circuit
where a large amount of series voltage NFB is
employed so that the voltage gain of the bjt is reduced
from a disgustingly non linear large number, say
100 times to say 0.99, and the open loop THD is reduced
100 times.

I see a dead horse being flogged very energetically. One word: Why?