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RE: clairty on a couple of issues

Posted by tube wrangler (M) on January 24, 2022 at 18:20:07

In Reply to: RE: clairty on a couple of issues posted by Ralph on January 24, 2022 at 15:06:30:

Makes sense, Ralph. One thing I have
neglected to mention is output transformer
windings.

A lot is said and done about proper output
transformer ratios-- what load a tube, operating
under a given set of conditions "wants to see".

This is done to minimize THD and IM distortions,
theoretically.

Things that never seem to get mentioned are of
far more importance: Power supply speed and impedance,
the size wire that is used on the output transformer
primary. This is a huge factor when it comes to
getting dynamic details delivered on-time.

The impedance on the primary is expected to reflect
a certain value to the tube(s) driving it, but nobody
even mentions the EFFICIENCY of the transformer wire
that is used.
(Fine wire with many turns is a good way to lose energy
transients).

I think most of us would agree that a 1200 ohm
primary in one transformer, and a 2500 ohm primary
in a similar model, where only the primary is different--
how many of us understand that all else being equal, the
1200 ohm model will outperform the 2500 ohm model.
That is-- with all else equal.

Vacuum tubes are great conductors when they're built
right, and when they're at the correct operating
temperature. Most of us assume that we can place
most anything the tube can handle on the grid, and
the tube will respond efficiently. What the same
argument doesn't state is that the other elements
in that tube are also very forgiving, and will
faithfully reproduce music if not abused in some way.

This allows the builder of high fidelity systems a
great deal of space/freedom in which to design-- as
opposed to someone who is asked to produce a given
amount of power, a given frequency response, and a
given set of distortion numbers.

Designers of vacuum tube systems designed to drive
high-efficiency, primarily voltage-driven transducers
don't have to obey all those rules. Instead, their
objective should be to get maximum reliability and
maximum sense of reality when listening to the effort.

Ralph, you're great as always-- I enjoy your posts and
also enjoy building things that deliver performance in
ways that are a requirement of years of audio experience,
and not a setup destined to satisfy only certain tastes
or certain kinds of music.

A good amp should deliver it all, keep individual acoustic
lines that are all playing at once-- both as single spaces
occurring in time-- and at the same time-- a coherent part
of a whole performance-- all of it coherent as a whole--
but with all of its parts reproduced equally well, and equally
in their own individual spaces-- detailed perfectly, regardless
of what else is being played in the overall performance.

Then, there are dynamics. Nearly all amps compress
something. I'm not talking about running out of power
here-- I'm talking about the amp running out of time-
spaces, where individual events occurring in an entire,
ongoing performance get added into each other and some
left out-- because the amp can't accommodate all of those
individual time capsules at once, reproduce all of them
at once as a whole, yet keep EACH one separately
identifiable in the mix-- an individual time space for
every kind of dynamic.

Usually large, high-power amps with separate power
supplies for various stages (like the 1950's "MAC"
MI-200 monoblock) can get a lot of this right, which
is why I once found a stash of them in an old movie-
theatre (Theatre-Chain owner)-- their retired equipment
area. They were using a 200 plus watt Hard-Rock Gold-Mine
shaker-table transducer amplifier to drive 3 watt Altec
speakers.

I bought them all-- 19 of them. Why were they doing this?
Was it power, headroom, frequency response, linearity,
or was it something else? Sure enough, it was the only
amp that "MAC" ever built that could make the timing events
in music play back like it had been recorded.

Of course, the amps had to have some help for me to like them.
Better caps, better wiring, better phase-inverter, one less stage,
provision for balanced input if wanted, etc, without compromise
(without using capacitors or an input transformer)-- Definitely items
I don't like.

It wasn't power. It wasn't linearity or frequency response.
It wasn't THD, and it wasn't IM ratings.

It was the ability to separate musical dynamics, yet play
all of them at once as a coherent whole.

Later, I learned that I could build a totally reliable
amp that would do the same thing even better- only a watt or
two, and no vacuum-tube maintenance needed. The humble SE
with a very careful build. Why? Because it's not Push/Pull.

It has only one active device per stage. This means that
the other of the circuit can't fill-in errors of omission!
The thing has to really work-- like Gangbusters!

-Dennis-

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