5B6 Bassman amplifiers had two 6SC7 or 6SL7GT pre-amp tubes, two 5881 power tubes and a single 5U4G rectifier tube.It was designed to generate 26 watts at an 8 ohm impedance load, and offered a cathode-based bias.While there have been periods of dramatic change—such as the transition periods between the Leo Fender years and the CBS years or the transition between the CBS years and the current ownership—most models are generally feature-specific and do not change from year to year.Serial numbers are also helpful in determining an instrument’s production year.
Hence during 1985 to 1987, production of Fender guitars was only done in Japan, while USA Fender created a new factory in California. BUT note that the "E" and "N" series does sometimes appear on "made in Japan" models. In any case, if it says "made in Japan", then it is... Fender has recently (in the last 20 years) introduced LOTS of different serial numbers schemes, depending on the country the Fender was made (USA, Mexico, Japan, Korea, etc). Sorry, since I do not collect new Fenders, I don't really keep track of these things.
Therefore, while helpful in determining a of production dates, a neck date is obviously not a precisely definitive reference.
Most specifications for a given Fender instrument model change little (if at all) throughout the lifetime of the model.
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.