What is the lowest voltage acceptable ?

I want to thank everyone for the valuable information. It's cooler today and the power is back to 120 volts. I use a Shunyata Venom PS8 with the plug in power filter, but I'm going to look into a Furman or Tripp Lite unit. 

I’ll also check out the PS Audio unit. 

Thank again.

Thanks again.

The older PS Audio Power Plant Premier works well with my 60 watt/ch tube integrated amp. It worked well with my previous SS 80 watt/ch amp as well. Dynamics is not compromised. Everything is significantly better than without it or with older Furman voltage stabilizer.

I would not, however, recommend this particular model. There were many reported reliability issues. I got lucky, my unit has been trouble free since new, that's more than a decade. And PS Audio stopped repairing this model, I think.