Can you do anything to make power tubes last longer ?

Yes, bias is adjusted individually for each tube, and I follow the manual. There is no range stated, there is a black dot you aligned the needle with, that's all.

Be sure you know what you are doing in setting bias on the low side.  If the measurement is in mA, the lower number means running the tube more gently.  If the bias is in mV, a higher number means lower current and gentler treatment of the tubes.

Be sure the voltage at your outlet is not too high.  I’ve seen 125 volts and higher from some outlets.  A variac, or even better, a stepdown transformer, can lower the voltage to something like 115 volts or lower.  Running tubes at, or slightly lower than recommended greatly improves life of tubes.

Be sure you know what you are doing in setting bias on the low side.  If the measurement is in mA, the lower number means running the tube more gently.  If the bias is in mV, a higher number means lower current and gentler treatment of the tubes.

Thanks for that, @larryi ; I was not aware.  I had read some stuff on bias before that had me confused.  However, my amp is biased using mA and I do run it a bit low.  

Lower voltage..

I use PS Audio regenerator that outputs 120V constantly, if you believe it.

But I noticed that, yes, input voltage is sometimes above that but never 125V.

1： do not turning on and off repeatedly 

2:   well-ventilated spot