Tube question

Just purchased an ARC D115 amp. Seller said the 6550s are all good, but said some of the output tubes may need replaced. But they all tested strong on my B&K tube tester -- except for the 12AT7 (bottom end of good). I have several old 12AT7s (RCA and Westinghouse) on hand that test quite strong. My question is: can I do a straight swap of 12AT7s without any biasing? My understanding is that the 6550's would need to be carefully biased and matched up, but that the 12AT7s can just be swapped? True?? TIA
Dave McNeilly
BTW has anyone tried to bi-amp with D115s? I'm going to give it a go...