Elliott Sound Products

Valves (Vacuum Tubes)
Index

Last Updated 26 September 2012

This section is about valves - aka vacuum tubes. Although
valves are a topic I've avoided since starting The Audio Pages in 1998, it's
quite obvious that they are not going away. Don't expect much in the way of
projects though. There are already countless websites that cover nothing else,
and adding more is not in anyone's interests.

Much of the material looks
at the basics - the fundamental info on valves. There is also introductory info
about the correct biasing of preamp valves and what gain you can expect from
traditional valve stages. We also look at an analysis of an existing valve
guitar amplifier, both to familiarise the reader with the basics of analysis and
to point out that "guitar amp" and "careful engineering" generally do not belong
in the same sentence. I've also looked at some of the myths that surround valves
- while they may have considerable nostalgic value, that doesn't make them
better than audio gear we can build today with more modern, lower voltage and
more reliable components.

The voltages used in valve (tube) amplifiers are
lethal, and must be treated with the utmost respect at all times.
Contact with power supply voltages may cause death or serious injury,
including but not limited to burns caused by the arc when contact is
broken. Never work on a valve amplifier unless you are experienced with
high voltage supplies, understand the risks involved and take proper
care to avoid contact.

Capacitors may store a lethal charge for a
long time after the amplifier is turned off or unplugged from the mains
outlet.

Do not wear rings or other jewellery that may become
caught on part of the chassis, thus preventing you from withdrawing your
hand if accidental contact is made. Ensure that all test equipment,
probes and leads are rated for the voltages you will measure. Ensure
that any operating valve equipment is secured from contact (electrical
or physical) by unsuspecting visitors, children, etc. Burns are not
uncommon with hot valves. Please remember that your pets may also be at
risk, and as de-facto members of your family it is your duty to ensure
their safety too.

Always remember that death is permanent, and is guaranteed to
curtail all interactions with the physical
world.

It will become obvious as you read through the various
sections here that I am not a fan of the Single Ended Triode (SET) amplifier.
There is much information in the following pages as to my reasons, but it is
very important to make one point very clear. At the height of the 'valve/ tube
era' (just before transistor amps took over), not one high-end manufacturer
built a SET design ... not one!  Without exception, the best
of the best (McIntosh, Quad, Audio Research, Leak, etc., etc.) were
push-pull.

Recording studio monitors and disc cutting lathes used these
very amplifiers (or others of similar design), and push-pull amps were (and
still are) also used by virtually every musician with a valve amplified
instrument. Single-ended amplifiers were (and are) the sole domain of cheap
low-end, low powered equipment. Practice amps, mantel radios, 'record players'
and the like used single-ended output stages because they were cheap and the
sound quality was considered 'adequate' for casual listening. With few
exceptions, these low-end applications used Class-A pentode output
stages.

Nothing has changed. The sound quality of a SET amp has
zero magic qualities, but it remains adequate for casual listening or as
a 'statement' (although I'm unsure what the statement might be). Claims that
these amps are 'hi-fi' are false - high fidelity implies that the integrity of
the input signal is not affected, but SET amplifiers often make profound
changes. Such amplifiers are effects units, not hi-fi amplifiers. For
those who enjoy the effects created, I say 'happy listening', and simply ask
that you don't claim that your system is high fidelity and/or has magic
qualities.

Title

Description

Date

Main Index

Articles Index

Lenard Audio

Introductory articles about valves and valve amps. Newcomers should
read this first

Introduction to Valves

General info about valve types, terminology and performance

Oct 09

Valve Amplifiers

Do they really sound different? Includes a review of one of my valve
amps

Nov 99

Valves vs. Transistors (Part I)

What are the differences? Surprisingly, not as great as you might
think.

Dec 09

Valves vs. Transistors (Part II)

There are some interesting differences that are not commonly
examined.

Sep 12

Bias and Gain

Understanding transfer curves, biasing and gain calculations

Oct 09

Valve Stage Analysis

Investigating an existing circuit to understand how everything works
(or doesn't)

Oct 09

Classes

Classes of operation for valve amplifiers

Jan 10

Design Considerations - 1

A look at the design process, and rationalising wishful thinking into
reality (Part 1)

Nov 09

Design Considerations - 2

Output and power transformers, DC filters, negative bias, etc. (Part
2)

Dec 09

Clipping

There's a lot more to guitar amp clipping behaviour than meets the eye
(or ear).

Dec 09

Intermodulation Distortion

The important relationship between 'total harmonic' and
'intermodulation' distortion.

Jan 10

Preamps

Obtaining very low distortion from a valve preamp isn't as simple as
it seems

Dec 09

Valve Myths

There are many valve myths, and some of the more common ones are
exposed.

Nov 09

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