[en] The strong field-induced quantum beats observed in beam-foil studies of Ly-α radiation are obtained in a conventional metastable-hydrogen quenching experiment. The phase relation between the Stark shifted 2ssub(1/2)-2psub(1/2) Lamb-shift oscillations and the much more rapid 2ssub(1/2)-2psub(3/2) fine-structure oscillations depends on the detailed way in which the quenching field is switched on. Apart from a phaseshift, the results agree with a non-perturbative theoretical calculation which assumes that the field is applied suddenly. Various frequency components of the time-dependent radiation intensity are identified with specific hyperfine transitions or groups of transitions. No adjustable parameters are used for the initial state amplitudes. (author)