If you’ve been interested in the subject of hi-fi for any length of time, then you’ve probably seen the word ‘valve’ banded about a fair bit – and maybe you’ve seen a few pictures of these enigmatic valves too. Maybe you’re even interested in seeing what these strange contraptions do/sound like. Well, we can help. With all of that. And we can even answer the ultimate question: What is a ‘valve’ anyway?
… What is a ‘valve’?
Put quite simply, a valve is a vacuum tube: a sealed container, void of any matter at all, which can be used to control electric current through something called thermionic emission. In physics, there is a type of particle known as a charge carrier which is able to move and carry an electric charge. These can take the form of ions, electrons, gases and ‘holes’, but in the case of vacuums, these charges are carried by free electrons known as cathode rays. These rays carry the charge – via the heating of the cathode or filament – over a potential energy barrier.
We call them valves in British English, although they have a number of names elsewhere. Some call them ‘vacuum tubes’, some call them ‘electron tubes’, and in North America they’re most commonly referred to as ‘tubes’. There are several applications for these tubes within electronics, all with small variations which make them suitable for their varying applications. Incandescent light bulbs were the first practical usage, but their use in audio and amplification wasn’t far behind. Within amplification, thermionic emission is used to amplify the power of an audio signal – making it louder.
History of Valves
It began in the late 19th Century, with a number of famous scientists and physicists such as Tesla and Goldstein who experimented with vacuums and ‘evacuated tubes’. The use of thermionic emission, as its understood today, was reported as early as 1873, but it was Thomas Edison who fully documented the phenomenon, dubbing it the ‘Edison Effect’. It wasn’t until Fleming took Edison’s bulbs – a very basic version of the lightbulb – and harnessed their full potential. His discoveries led to the Fleming Valve – which he called an Oscillating Valve due to the current passing in a single direction – and the origins of the valves we know today was born! Fleming’s advance on Edison happened in 1904 while he was working for Macaroni – a British telecoms company. The earliest valve that functioned this way was called a diode – but it wasn’t until 1906 when a Lee De Forest added a third electrode that the first amplification device was born.
Valves as amplifiers were – from then on – in steady use in all devices that required the amplification of an audio signal – radios, music amplifiers, early telephone signals and even televisions. Advances were made over the decades, such as the invention of negative feedback – which allowed for cleaner signals and improved audio quality. The greatest advances occurred during the post-WWII boom, when the consumer market was heaving and a call for higher quality audio by the consumer market was made. Up until the 1970s – and the development and popularity of the solid state transistor-style amplifier – valves were the only available method of amplification. The decline from the 70s onwards was steep as transistor-style amps – and their benefits in terms of efficiency and longevity – took the market by storm.
But that wasn’t the end for the trusty valve amp. Not at all.
The Transistor
In 1954, the transistor was developed, which functioned in a similar way to the valve – with the active component being a semi-conductor device (which can exploit the electronic properties of materials such as silicon, which means a current can be altered in a solid state, rather than through the use of a vacuum or gaseous environment. This solid-state method was an instant game-changer. There was no need for a ‘heating’ of a cathode, or any ‘warming up’ time, which meant this new method was incredibly efficient. By the 70s, the transistor method was preferred, owed to its comparatively smaller and lighter stature (which leant itself well to multiple applications, energy efficiency and greater robustness and longevity. It was around this time that amp classifications were introduced, so the applications of different types of solid-state amp could be best described, including in comparison to valve amps, which were from then on classed as Pure Class A.
We’ll let the experts at Arcam take it from here… (read the whole thing!)
CLASS A
“The simplest audio amplifiers are single-ended and Class A; that is they make use of just one output transistor which is always conducting, irrespective of the output signal waveform. Class A has good to excellent linearity (and thus high fidelity / low distortion) but very low efficiency. It is almost never used in a power amplifier’s output stages but is ideal for the input and high level driverstages of a power amplifier.” – Arcam
CLASS B
“Class B amplifiers are much more efficient than Class A amplifiers but they
have high distortion due to gross non-linearities at the crossover point, which
is where the two transistors transition from on to off. This form of distortion
– called crossover distortion – is extremely unpleasant to the ear and thus no
commercial amplifier designs use pure Class B.” – Arcam
CLASS A/B
“A combination of Class A and Class B, the Class AB amplifier has a much higher
efficiency than Class A but much less distortion than Class B. This is done by biasing both transistors to conduct a little at and near to zero signal output – the point where Class B amplifiers introduce gross non-linearities. They then transition to Class B for larger signal currents […] Most commercial power amplifiers are Class AB designs.” – Arcam
CLASS D
“Class D amplifiers use a different technique in which the output transistors (usually MOSFETs) are rapidly switched on and off at a far higher frequency than the highestaudio signal that needs to be reproduced […] The advantage of Class D is its high efficiency (80-90%) because the output transistors are either turned fully on or fully off during operation. Its quiescent power consumption is comparable with a Class AB amplifier […] In general its sound quality is not as good as a decent class AB amplifier, although the gap is narrowing.”
So… why Choose a Valve Amp?
You’d be forgiven if you’ve reached this point thinking that a solid state amp – particularly one with a Class A/B or even a Class G amplification is the best way to go. But you’d only be half right! Valve amps didn’t go into extinction upon the invention of the semiconductor, nor did they fade into obscurity. With the rise of high fidelity, enthusiasts would gradually move back into the realms of the Pure Class A that valve amps offer. For all of the benefits of the transistors, there has yet to be one that can fully match the warm, lush and wonderfully pleasing sound that those valves provide. There’s far more to them then just the novelty of the warm glow of the cathodes (… we’re not doing to besmirch that, mind you, it’s a beautiful thing!), with proper care and respect, many of the foibles of the valve can be overlooked – or over turned – and your reward is a sound that is virtually unparalleled by transistors.
The valve amp – which is still being developed and modified to this very day – has made something of a comeback in recent years. And not just among the die hard hi-fi aficionados (they never gave up on it, lets face it!). That pure, warm and lush sound has been seducing the ears and hearts of relative newcomers, who see past its shortcomings to the most important principle, when talking hi-fi: the sound. And the sensation it causes.
True hi-fi cares not for efficiency or practicality. If it has those things it’s a bonus of course. But what it truly belongs to is the sound. And a valve amp embodies that notion more wholly than any other hi-fi product.
Curious? Give us a shout and come have a listen. We have some lovely specimens in our showroom and frankly, we love showing them off.