Some individual lines of Tennyson's "Charge of the Heavy Brigade" are perfect amphibrachic pentameters, but he does not try to maintain that exact rhythm in the poem. Some lines lead off with dactyls, some become anapestic. Here is a series of amphibrachs, with the last truncated by catalexis:

   *     /     *  | *    /   *  |  *      /         * | *      /      * | *    /     (*)
The trumpet, the gallop, the charge, and the might of the fight!

This could also, of course, be scanned as anapestic pentameter: * / | * * / | * * / | * * / | * * /