In article .com,
Andy
Evans wrote:
Note that most transistor amp designs tend to have a flat response, low

distortion, and a low output impedance. Whereas zero-feedback 'SET'
designs tend to have a tailored response, distortion that rises rapidly
with output, and a relatively high output impedance. All of these
factors may cause the SET design to change the signal patterns and cause
audible changes in some circumstances.

It may be useful to seperate out some of the commonly used expressions
regarding SETs and valve amps, since I know several have been confused.

a) One of the common characteristics of SETs (though NOT implicit in the
term "single ended triode") is the use of a DHT (directly heated triode)
in the output such as 2a3, 6B4G, 300B and 845 - this can be a major
positive factor in the overall sound, against which can be set the
drawbacks Jim has listed above. .

You may have to explain why. 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. I had though that valve designers largely abandoned
direct heating of the cathode for various reasons. Hence the comments you
made (that I snipped) about having to search for small-signal direct heated
valves mainly from 80 year old stock.

It is obviously up to the OP to choose what they prefer. However I suspect
he would find it rather easier to get good results using a design that does
not rely on such.

Similarly, if he wanted to build his own AM radio, I'd be inclined to
suggest he used modern detector diodes, not a 'coherer'... :-)


b) When we come to DHTs we are in another ballgame, in my opinion. Those
who habitually use DHTs, do extended listening tests with DHTs, and are
familiar with their characteristic sound will claim they offer quite
audible gains in clarity over indirectly heated valves.

The problem for the OP here is that you may simply be giving opinions for
which there is no reliable evidence. As, indeed, you warn. Hence there is a
risk that what you say will simply impede his progress.

Slainte,

Jim

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