Using autotransformers

I have read (and re-read) all of your posts - Thank you! Yes, Al, you were right. I was considering an autotransformer as defined in Wikpedia. The idea was not mine but someone who works on all forms of electronics. Now I am wondering if looking for something that would control the entire house might not be a better choice. We currently have voltage regulators on most large appliances, including the APC battery back-up but nothing on the amps.

All of the options look expensive, OTOH, paying 1,000 to repair an amp is not cheap either.

I will look harder at the Variac and see if that makes sense.

Thanks to each of you for the input.

Often as high as 130-135 Volts and on other occasions it would drop to below 110.
04-28-13: Puerto

Your profile says you live in the USA.

If you live in the USA contact your power company. Power companies here in the US are regulated by the state. Most if not all require a max voltage variation of + or - 5% average, RMS.
120V being the base line. + 5%) 126V - 5%) 114V.

Now if you are experiencing low voltage at times in some parts of the house and high voltage in other parts of the house at the same time that is a horse of a different colour.
That usually indicates a loose service entrance neutral conductor.

I do not live in the USA. I now live in Mexico.

I do not live in the USA. I now live in Mexico.
04-29-13: Puerto

Puerto,

You do have a few options.

* Sell the Krell mono blocks and buy amps with auto input voltage sensing.

* Install a Constant Voltage Transformer, CVT. Also known as a Ferroresonant transformer.

* Buy an Automatic Voltage Stabiliser, AVS.
Example of, http://www.monstercable.com/productdisplay.asp?pin=2137
.