How can I tell?

I bought a 112RP 100 and the seller had EL34 tubes in it, saying the amp may have been modified to use them instead of 6L6 tubes. How can I tell if the amp has been modded? If it has NOT been modified, is it safe to just use 6L6 tubes and set the bias? Did ANY 112RP 100's ever come from the factory with EL34's?
Thanks.
LRMars

Larry,first look for the little sticker inside the cab this should tell you what this amp at least was sent out with.depending on the year ,yes your amp could have been made to use el34s.you didn't mention the year of this amp ,if its got the black logo/silver background one it probally did use el34s,thing is 6l6 and el34 are not what i'd call direct replacements,so yes if that amp called one and you got the other i'd just be getting new tubes forget the biasing most latter models of these amps were self biasing anyway.meaning wrong tubes will either burn out quick or sound bad.