BUR #3053 has been approved by @evazion.
mass update amplifier -> amplifier_(instrument)
The tag is almost exclusively used for electric instruments and the amount of posts that may contain different kinds of amplifiers (eg. Headphone amplifiers) is small enough to go and correct them manually.
Tagging it as guitar amplifier would be too exclusive as bass amplifiers are often visually distinctive from guitar amps, more commonly in terms of scale and height. Was considering naming it as instrument amplifier.
I'm also considering doing some more BURs to shine and fix up musical equipment tags but I'd rather go one step at a time rather than doing fast wrong steps.
EDIT: The bulk update request #3053 (forum #169608) has been approved by @evazion.
Updated by DanbooruBot