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.
and Canadian English) or (thermionic) valve (outside North America) is a device generally used to amplify, or otherwise modify, a signal by controlling the movement of electrons in an evacuated space.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.Amps should only be serviced by a qualified technician.Model/Circuit Number: Years of Production: 1972 – 1982 Era: Silverface Configuration: Combo Controls: Silver forward facing w/ blue labels Knobs: Black skirted w/ chrome center, numbered 1 – 10 Faceplate: Comments: Some later Bassman 10’s had a MID control on the bass channel.Transformers are used to convert between high and low voltages, to change impedance, and to provide electrical isolation between circuits.This is useful in converting the voltage from a wall outlet, typically 120 or 240 volts, into a higher voltage required by tubes in tube amps .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.typically 400V or more, and a lower voltage for the tube filament, typically 6.3 or 12.6V. Dating Marshall Amps In 1969 Marshall introduced a date coding system.Some of the older Marshall amps have an inspection sticker on the top of the chassis which usually has the day, month and year the amp was actually made or inspected. Note, "A" Date Code ran for 18 months (July 1969 to December 1970) so the "B" date Code was never used and has been omitted. The serial number is generally located on the back of the chassis but from 79 to 80 it was on the front panel.