Arnie Peskin
ENGINEERING.com
There was a time when the vacuum tube was practically synonymous with electronics. Then, about sixty years ago, semiconductors began to replace tubes in one application after another until tubes became museum pieces. But there were a few applications where tubes never fully disappeared. And recently they have been making a comeback.
When semiconductors became widely available, their advantages were immediately clear to engineers and technicians. They were smaller and lighter. They took far less power to function. They had better reliability. And probably most importantly, their characteristics were far more linear and stable.
Early TV sets were large pieces of furniture with dozens of controls on them, front and back. Those controls, with odd labels such as horizontal hold and vertical linearity, were all needed in the course of an evening's viewing, since the capabilities of their components would drift with heat and time. Many a breaking news event had no video feed because it took 20 minutes to warm up and tune the cameras. In those years, TV took skill and patience, whether you were on the production side or just trying to watch.
Transistors and integrated circuits quickly replaced tubes in consumer electronics and industrial systems until recently when something unexpected happened; certain niches began to extol the virtues of tubes. The first group was musicians and audiophiles. They claimed that tube-based amplifiers provided a sound more to their liking. Upon closer analysis, it seemed that these people had fallen in love with certain characteristics that others would term distortion; that is, the amplifier signal out was not quite the same as signal in, but instead provided the overtones that they had come to expect and value in their listening experience.
There are other areas where tubes are coming back or never totally went away. In applications where high power output is required, tubes can usually be deployed more easily that semiconductors. In applications where high radiation is present, tubes have proven more rugged.
Perhaps the strangest argument in favor of tube-based apparatus is an aesthetic one. Tube equipment seems to have a distinct effect on certain technology professionals who work with them. When a vacuum tube-based chassis is in operation, its filaments produce a purposeful glow – they LOOK like they are working. There is also an unmistakable smell to such equipment (which is probably the odor of baking dust, but still charming to those who grew up with them). Whatever the reason, other factors being equal, many enjoy working on vacuum tube equipment.
It is hard to find reliable trend figures for vacuum tube sales, but it a modestly flourishing industry, especially in Asia. This upward trend in tube usage isn't going to scare the semiconductor industry. Their rosy outlooks based on Moore's Law won't be affected. It is certainly true however, that there is a future for this venerable technology that designers and techs should not ignore.
