However, tubes are still used in several specialized applications such as guitar amplifiers (also called a valve amp outside the U.
S.) and high power RF transmitters, as a display device in television sets and in microwave ovens.
Eventually, I thought, I'll get a rough idea what the highest and lowest s/ns were.
Replacement tubes and transformers are readily available for these amps however there are many boutique amp manufacturers making new tube amps with a vintage sound.
A transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling with no moving parts.
The result is a current of electrons flowing from filament to plate.
This cannot work in the reverse direction because the plate is not heated and cannot emit electrons.
It consists of a minimum of two coils, the primary and the secondary, wound on the same core.
An alternating current in one winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings.
The simplest vacuum tubes resemble incandescent light bulbs in that they have a filament sealed in a glass envelope which has been evacuated of all air.
When hot, the filament releases electrons into the vacuum: a process called thermionic emission.
From 1969 to 1983 the date code was after the serial number.