Voltage regulation

I have noticed that my dedicated mains power slowly fluctuates between 124 and 127 volts. Nothing seems to correlate like furnace - refrigerator turning on and off - time - day of the week etc. I'm looking for something that would keep the output a steady 120V without constricting the current. I'm not looking to break the bank but would like any and all suggestions.

The reason I'm looking for this is because I have a tube integrated where the bias goes up and down with the voltage fluctuations.

Post removed 
10 volt swing per day WOW. As far as linear power supplies they are generally designed to work with +/- 10% of the standard 120v. So for me I would think 132v would be my upper limit. At any rate I have been trying to keep my bias down. I've lost 4 tubes in 4 months. All in different locations in my integrated. 2 tubes blew when no music was playing.
My personal measurements taken at my house rarely see over voltage . What I have seen however, especially in the summertime are very low voltages, as low as 90 volts. I don't think it's simply the utility company rolling a brown out, because my folks up the street never have the issue. In fact, anytime the compressor for my central AC kicks in, I've seen the street light dim, regardless of summertime demand conditions. I think the transformer on my street isn't rated high enough, or the lines feeding it don't have enough current behind them. During these extreme brownout periods, I turn off as many motors as I can, but I wonder if I'm doing any harm to my audio system.
I use tubed amp and a voltage regulator Exact Power EP15A...it holds the current at a constant 120 volts....good for tube life and also sound. there are others out there that do the same thing.

It could be the Single Impedance Output Transformer in your amp. Have you called the manufacturer or distributor and asked the question as to why this (blowing tubes) could happen?