In article .com,
Andy
Evans wrote:
(DHTs sounding better than directly heated valves) You may have to
explain why (Jim).

I may not - your need for theoretical knowledge is considerably greater
than the average, and many people build equipment empirically - they put
a circuit together, listen to it and measure it, then start changing it
until it sounds better to their ears. I'm sure there is an explanation
somewhere, but on a day of 35 degrees centigrade I'm damned if I'm going
to hunt around for anything.

I'm afraid that translates as "No evidence, just opinions presented as if
they were facts". :-)

Since I am not particularly expert on valves I am unsure why you believe
direct heating is a "major positive factor" in terms of the results.

As I said, I and a few others (audio designers and EEs just for the
record) have been working with DHT small tubes for quite a while now,
building numerous circuits and subjecting them to listening tests. We
believe in DHTs on the basis of the results we have found, and our
responses to listening tests have been very close. The differences are
quite marked.

So has anyone demonstrated they can:

1) hear these "quite marked" differences in a suitable test - i.e. one
whose results can be subject to statistical analysis, etc?

2) Show any theoretical analysis or measurements to give a plausible
physical reason?

I can't recall hearing any reports to this effect, or reading any. I can,
however, recall hearing all kinds of unsubstantiated opinions presented as
definitive 'conclusions' about such matters.

That you and some anonymous 'EEs' "believe in" them is a declaration of
personal faith, not evidence, I'm afraid. I suspect that many more 'EEs'
*don't* believe anything of the kind, but that wouldn't be evidence, either
- but it may put your faith into context.

I had though that valve designers largely abandoned direct heating of
the cathode for various reasons.

They indeed did - the reason, as I said, being that current production
of them stopped in the 30s for the most part. Designers use current
production parts.

I'm afraid you may have a problem with the above argument. In logical terms
it can be explained by the 'cart:horse' operators not being commutative.
:-)

I would suspect valve makers stopped making direct heated valves because
the people who wanted to buy valves started buying - and preferred - those
which were *not* direct heated.

However, as you say, you are under no obligation to anyone to provide any
evidence for your assertions. The OP and others can judge your opinions on
the basis you have chosen to provide.

Slainte,

Jim

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