[Nick Gorham]

Ian Iveson wrote:
How would you explain to a novice how to design a valve
amplifier?

I see two possible approaches. One way to begin is to
establish the purpose of the machine, divide that purpose
into a series of processes, and develop a block diagram of a
generic amplifier. The other is to examine various circuit
fragments in order to understand how they, and their
components, behave. These two approaches may be termed "top
down" and "bottom up", respectively. Most books on design
cover both aspects, in one order or the other. Both can be
dealt with using the common logic of analysis.

Both are problematic. Whichever aspect the novice encounters
first, he will be bemused for lack of prior understanding of
the other. It's hard to grasp a block diagram without
knowing what might be inside the boxes and why; and it's
hard to grasp a fragment such as a mu-follower without
knowing what it might be used for and why.

Perhaps the novice could be reassured if, in a preface, the
author were to acknowledge these problems, and provide some
logic that the novice might employ to guide him through the
process of learning to design?

This year I have resolved to write such a preface. Ideas are
welcome.

Is the process of design predictable? Can you characterise
the logic of development, from start to finish?

The best structure, by far, I have come across is in the
late J L Hood's "Valve and Transistor Audio Amplifiers".
Typical circuits are introduced and analysed in historical
context, so the reader becomes aware of the issues in just
the same way as history did. However, the reason for using
such a narrative style is not made explicit, and so the
novice may not get the point.

New valve enthusiasts, and especially young people, are
needed or there'll be nothing left when we all die.

Which won't be this year, I hope.

Anyone else made a resolution.

Best wishes,

Ian






Well, with respect, I think you have decided to solve a problem that you
have decided exists, but in my experence doesn't in the real world. As a
programmer who started in the 70's I am well aware of the top down and
bottom up design methods, and both work just fine, the only issue is the
middle out one.

From what I have seen, Phil's answer is just about on the money, people
start wanting to build valve amps because they want to use valve amps.
They already have a goal. And they resolve this by either building a
kit, or a existing well documented design. Some never go further than
this point. But some want to know a bit more, so they read a lot of
books, ask a lot of questions on the internet, and try and follow the
design patterns that already exist, mix and match them to fit their
needs and interests. Some then never go past this as they have a block
about maths, so they never go beyond graphical methods. Then a few more
progress to the point of trying to get to the level of understanding of
a EE in the 1950's. But from what I have seen those that try and get to
the 1950's level (I am trying hard to get there myself) normally have a
fair bit of EE education in their background anyway, so they don't need
the basics explaining to them, and if they did, they know what books to
read to try and make up for the lacks in the education.

There are a few on the fringes that are doing things that were not done
in the 50's, but they are not inventing new topologies, they are just
updating older ideas using components that were not available in the 1950's

In the people I know (which I imagine is a small but representive subset
of the rest of the world) who mess with valves, there are folk in all
the groups, and there seems to be no lack of interest in learning and
building.

In terms of progress, in my view its simple, 1. Build a kit, 2. Read
Morgan Jones, 3. Buy a copy of RDH and read. 4. Keep reading RDH. And
between 1 and 4, build, tinker and measure a lot.

--
Nick