i recently bought a laney lc15 amp as new threfore came with the standard cheapy tubes.

i wanted to put some decent tubes in it to get an even better sound out of it but tbh i dont have a clue.

what would you recommend changing? the preamp, the output tubes or both?

i've heard a lot about amps needing rebiased when changing but i dont know when this applies.

say if i bought a matched set of jj el84s could i just stick them in without a hitch or would this be an example of the amp needing rebiased, the instruction manual is pretty vague with its description.