Valve-equipped power amplifiers have enjoyed a resurgence of late, and there is a myriad of specialist companies selling them on the internet. So what’s so good about these amps in the first place, and more importantly, why did they go out of fashion? To explain, a bit of history is needed:

Over 100 years ago in 1904, John Ambrose Fleming concocted the first and most basic version of the valve used in power amplifiers. Called the ‘thermionic valve’ this device used heat to stream electrons (current) between a cathode and anode, within a vacuum. John called his creation a ‘diode,’ because of its two electrodes (anode and cathode), and it was put to use as a radio detector and rectifier.

It wasn’t until a third component was added to the diode, (now called a ‘triode’) that the valve as we know it started to take shape. Lee De Forest added a ‘control grid’ to modulate the current of electrons that flowed within the tube. Triodes could essentially ‘amplify’ current, and found their first use bolstering degraded telephone signals.

Over the next few decades, the valve gave rise to all sorts of electrical products including radios, industrial machinery, telecoms systems, and even the first computers. The post war era was the valve’s Golden Age, where cheaper prices, growing consumerism and new technologies culminated with devices such gramophones, black-and-white TVs, full range loudspeakers, and the valve amplifiers to drive them.

While valve-based amps were widely used during the 1960s, their demise was already under way thanks to the development of the transistor back in 1947. Once perfected, transistors were smaller, cheaper to produce, required far less power, didn’t get hot and offered reduced distortion levels. By the 1970s, transistors had replaced most valves in electronic devices, although some valves were still used in niche applications that required high power and frequencies.

McIntosh's MC2301 monobloc tube amplifierThe modern-day audiophile’s amp of choice: McIntosh’s MC2301 monobloc tube amplifier.

Valve-based amplifiers have clung to life largely through the influence of audio enthusiasts who claim they provide better sound than their transistor-laden usurpers. Described as ‘warmer’, sound signals from valve amps have less harmonic distortion, and very wide bandwidth – enough to drive high loads that would cause ordinary amps to stutter and die – and at low volume levels, valve amps have minimal distortion. Plus, the warm glow from the valves themselves appeals to many.

On the downside, valves do burn out, and like a light bulb, are quite fragile. Also, the amplifiers themselves can be very dangerous because of the high voltage needed (around 600 volts DC current) to operate, and they generate a lot of heat – all of it wasted energy. Still, despite the finicky nature of valve amps there is life in them yet, especially if analog sound is your perception of ultimate sound.