I am making a “Vintage Voltage” unit that supplies drop-down voltage through a bucking transformer to supply the user with three optional voltages to an amp: Line voltage (125 VAC), minus 6 V (119 VAC) and minus 12 V (113 VAC).
Because our vintage amps were designed for voltages from 110 to 117 VAC, it is important to supply it with the correct voltage. Voltage that is too high can shorten tube and capacitor life, and also change the tone of the amp.
This device also provides EMI filtration and spike protection, as well as setting an alarm if the ground is missing or the polarity is reversed, an all-too-common occurrence with wall power in questionable venues.
It is ground issues and reversed polarity that has shocked many musicians, and in some cases has resulted in death.