I owned the Apollo 2's for a few year. I used 842's, and VV52B's, and KR 52BXLS's. All were fine. I lowered the filament voltage to that of the 1.5's so I could get a bit more tube life. This actually made tha amps sound better and eliminated any premature tubasides! I use a Gatekeeper with soft start and this also prolonged tube life. There were a batch of 842's and a batch of KR 52BX's that didn't last long. The last set of 842's sounded great and were reliable. I think each tube had it's own sonic strengths and weakness. I think I liked the 842's the best. I believe the AVVT has a tube that will run in the Apollos. Maybe a 520 or something like that.
Good luck
