Dating a fender twin reverb
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.
Vacuum tubes, or thermionic valves, are arrangements of electrodes in a vacuum within an insulating, temperature-resistant envelope.
Although the envelope was classically glass, power tubes often use ceramic and metal.
Fender switched back to the blackface era cosmetics some time in 1980.
Twin Reverbs produced between late 19 have a black control panel and silver sparkle grille cloth.
However, tubes are still used in several specialized applications such as guitar amplifiers (also called a valve amp outside the U.
An alternating current in one winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings.
From 1969 to 1983 the date code was after the serial number.
From 1984 to 1992 the model number was first, then the date code, then the serial number.
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.