"Andre Jute" wrote in message
oups.com...
Trevor Wilson wrote:
"Andre Jute" wrote in message

Trevor Wilson wrote:
Patrick Turner has proclaimed that none of what I wrote
is correct.

All of this depends on the assumptions under which we are operating.
You and Patrick may have less bother if you agree ground rules. This
isn't a knock. I made the same error: I thought you and I had a set of
assumptions agreed but it turns out not to be so when you say:

However, all
things being equal (or as equal as can be, PP will be superior).

The horses for courses assumption, supported by the above, which I
thought we had in common, is totally reversed in this exchange:

Andre offers Trevor a handicap: You can assume the worst condition for
SE (zero negative feedback) and the best condition for PP (all the
negative feedback even an incompetent designer may want), and I'll
still whip your ass.

**Nope. If your hypothetical SE(T) amp uses no Global NFB, then so too
does
the hypothetical PP amp. Same output tubes, same Class A bias, similarly
sized power supply, etc, etc. Let's compare apples with apples, not
apples
with bricks.

Oh dear. I was operating under assumption that all things are not
equal, not in the sense you elaborate above, that instead we are
positing a comparison between median real-life amps.

**That would be a really dumb way to compare topologies. If you are
comparing topologies (which we are) then we need to eliminate as many
variables as it is possible to do. Global NFB vs. zero Global NFB is a HUGE
variable.

For instance, a
modern ZNFB SET amp is deliberately designed to be much flatter than
say fifty years ago, while the PP amp will have much more power (than
the SET) with NFB silencing it. That changes my view on these matters
that you raise, even in the first (strictly technical) round where I
agreed with you, the second harmonics matter excepted. I read "similar"

**When I say "similar" is mean SIMILAR. All the way down to the type of iron
used, tube types, resistor types, HT Voltages, bias currents and NFB
arrangements.


in a very much wider context of merely meaning "competent" or "of
presently acceptable design", whereas you (and John and Chris) are
reading it as literal sameness, including precisely the same tubes at
precisely the same power output with precisely the same NFB, which you
specifically state later on.

**There is no necessity for a PP amp to use Global NFB. If you want to
compare non-Global NFB SE(T) amps, then compare them with a similarly
configured PP amp.

If that sort of *equality*, meaning precise similarity to the greatest
possible extent achievable, is the rule under which we're operating (a
stupid ****ing way to proceed,

**Huh? If you're comparing output stage topologies (which we are) then it is
the ONLY way to proceed. Otherwise, you're just comparing different iron,
different NFB schemes, whatever.

even if more scientific--nobody would
choke a PP amp down like that), I must be a greek giver. I cannot agree
with you an any point in the first round except the second harmonic.

**Then you need to do more reading. Or testing. You choose.



* ALL SE amps suffer from even order harmonic distortion, which is
automatically reduced by using push pull topology. IOW: All things
being
approximately equal (same output valves, high quality iron, good power
supply, same bias current, etc) push pull will outperform SE.

True. A great advantage, much more pleasant than the odd harmonics of
PP even when the latter is at a much lower absolute level.

**Huh? In which universe do you imagine that higher levels of distortion
will lead to greater fidelity?

But in this
contest, with both amps operating under the same conditions, they are
assumed to be designed so that the harmonics of any nature are
imperceptible.

**A bold assumption. Under what conditions can your SET amp acheive that?


* ALL SE amps suffer appallingly bad load tolerance. IOW: A 20 SE amp
(at
or
near clipping) will deliver 10 Watts @ 4 Ohms, 5 Watts @ 2 Ohms and so
on.
Unless the user has an almost resistive load, then severe power
problems
can
be expected. This problem can be eliminated by using push pull
topology.

When the two amps use the same tubes under the same operating
conditions? Rubbish. That's why I tried to give your beloved PP a break
so you could win something in the first round.

**Huh? Let me spell it out for you: When your SE amp (of ANY variety) hits
it's maximum peak current, not only does it cease to be operating in Class
A, but it ceases to be an amplifier. *ANY* PP amp, will still continue to
act as an amplifier, even after it reaches a point where more peak current
is demanded, beyond it's bias point. It simply begins operation in Class B.
IOW: The worst case scenario will be that a PP amp will deliver
approximately similar power levels, even as the load impedance is halved. A
theoretically 'perfect' amplifier will, of course, double it's power as the
load impedance is successively halved. Therefore, *any* SE(T) amplifier is
the complete antithesis of the perfect amplifier.


* SE amps are MUCH less efficient that a similar power PP amp.

In Class A?

**Yes. Want that RDH4 quote again?

Replace the loud "much" with a whimpered space, and I'll
agree.

* SE amps, generally, exhibit higher levels of hum and noise than PP
amps.

This is entirely an irrelevance in modern amps where we know how to
reduce levels of hum and noise to better than acceptable levels. It is
a petty point applicable only to the cheapest commercial amps. We're
talking about a different class of amp.

**Fair enough. Nevertheless, it is a fact of life that PP confers an
automatic reduction in hum an noise.


* SE amps have a lower damping factor than a similar PP amp. This may
lead
to audible frequency response problems, within the audio range.

I withdraw my original highly qualified agreement, given under a false
assumption of amps of standard design for their class rather than
artificially similar as in the new rules.

**One must compare apples with apples.

Have it your way, Trevor. In that case, under the present rules your
statement is incorrect.

**Huh?


**I have no issue with PP, of any persuasion. PP eliminates or reduces
most
of the problems associated with SE(T).

But Trevor, there aren't any problems remaining.

Under the new rules of equality, where I am defending ZNFB Class A SET
against Trevor's ZNFB Class A PP, push pull topology simply does not
have any technical advantage over SET, and in real life where the PP
amp would use beam or pentode tubes and the SET a DHT, the SET has all
the advantages of its built-in NFB.

**I suggest you read the sections I've previously cited from the RDH4. Your
knowledge is seriously deficient. Unless, of course, you feel that the autor
of the RDH4 was wrong.


--
Trevor Wilson
www.rageaudio.com.au

You shouldn't have changed the rules Trevor. Under the new rules you
cannot prove superiority for PP amps.

**I changed nothing. When comparing topolgies, it is appropriate to compare
ONLY the topolgy.


Not that anyone changes behaviour, of course. You will play your
beloved PP and I will play my beloved PP, and my beloved SET, and my
beloved solid state. We'll both still be listening to the speakers, not
the amps.

Thanks for sparring.

**Sparring? What's with boxing metaphors?


--
Trevor Wilson
www.rageaudio.com.au