sonic frontiers sfl80 arcing problem

I have a sfl 80 amp that arced under one output tube. It happened a few months ago and recently at the same tube. After reseating the tube it seems to be fine. Should I have any concerns? Also the bias for the tubes is suggested at 50mA. I've set it just under that but when I turn off the amp, the meter jumps to 80mA then decays to 0,is this normal? Thanks for your input.
no. sounds like you may have a problem with a cap which is dying(or a resistor?). take it into your local tech and have him check it out. I had a similar problem with a SFM 160.