That is very interesting. I often wonder from day to day if its my amp or my ears that are the problem when the amp seems to handle differntly. I will have to check mains on a good day and on a bad day to compare voltage difference.
In the US alot of people are using Furman power conditioners, Not sure if they make 220-240volt but I believe they keep the power at the right level as well. Have you tried anything like that?

I think the short answer is anything that can keep the voltage constant and at the voltage the amp was designed is the ideal situation. I've been wanting to get a real AC regulator (Furman) for quite a while now. It's just that the true regulators are a bit pricey.

While the US's mains voltage can vary the issue I find is that it runs a bit higher 125v instead of 120v. And this is something I've been just now pondering with recent completion of my amp. My mains voltage is constant at 124v-125v. So I biased it based on this. Now that I've been checking all the voltages and see what different mains voltage will do to the overall measurements, it makes me want to get a regulator even more.

Like Todd has mentioned I know I have had my other amp feel different from place to place. Although I'm usually more concerned and dealing with dirty AC, which is something else most of regulator/conditioners will help.

I would think that while the voltage difference that the individual components see when the mains is not ideal, it would be the difference in bias that would produce the biggest effect of tone and feel.

Sounds like a good idea, Nik.

Furman Voltage regulator are available in 230/240V AC but they are no good for tube amps. They won't harm them but they can't keep the voltage within +/- 2 VAC of the specified 230/240V. They have a +/- 10% so that means if the voltage is within the range of 240V you will still get a varying voltage until the voltage either exceeds 240V by 10V or drops 10V below.  Obviously 240 is not what you are going to get from your socket all the time. I find with tube amps especially if the internal/plate DC voltages are high. My custom buily Barwatt "Super P.A"100W 1968 circuit amp runs at an internal 475 VAC. Even small fluctuations in AC voltage, I'm talking 2 VAC, you can here the difference. The builder set the tubes bias with a outlet voltage of 240VAC. If the voltage is running high, say 245 V the amp sounds brighter, harsher and not so good.

When the voltage drops below 240V to around 238V it sounds excellent, further drop in voltage to around 232 V it again starts to sound bad.

Bands/Musicians like AC/DC and Joe Bonamassa and many more use Kikusui (Japan) voltage regulators. They are quite expensive but they can be used anywhere in the world, you can set the voltage to just about any voltage you desire and it will keep it within +/- 2 VAC of your desired setting( on the 200V setting) and +/- 1 V on the 100V setting. They can store  up to 4 voltage programmes and you can select between 50/60hZ. There is a whole range. I think the smallest  is 500 KVA which I think is enough to power a 100W tube amp.

AC/DC (Angus Young) uses the largest which can power up to 12 x 100W amp heads. His amp tech swears by them. They are essential to maintain a consistent tone worldwide.

There is a Youtube video, a rig rundown either of AC/DC or Angus Young's gear.

I am going to get one when I can afford it as I am getting so frustrated by inconsistent tone from my amps.

I'm in Australia and we have a nominal voltage of 240V at 50 hZ.  I have a plug in voltmeter and it shows that the voltage here is constantly varying. The highest I've seen is 250.8 VAC and the lowest 231 VAV.

I don't bother playing if the meter reads over 245V as the amp just doesn't sound great.  You can actually hear the change in tone when you are playing when the voltage changes by just a few volts.

Furmans' will protect your gear and correct the voltage if it is 10 V either side of 230/240V. I had one and I'm not really sure it did anything to keep the tone consistent. They can be set to 230 or 240V AC.

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The issue of mains voltage and its potential impact on audio equipment like amps is an interesting one. While the EU did aim for voltage harmonization, it's true that there's still some variability across different regions and even within the same region due to factors like demand fluctuations.

Changing your house voltage to 220V using a product like the one you mentioned could potentially have some effects on the performance of amps from other countries and UK-made amps. Lower voltage might slightly reduce the output power and affect the tone, potentially making it sound slightly different. However, whether this change is noticeable or preferred is subjective and depends on your personal taste.

Consistency in voltage throughout the day can be an advantage for sensitive equipment, but om production's modern amplifiers often have built-in voltage regulation to handle minor fluctuations.

Ultimately, the decision to invest in a product like the one you mentioned should be based on your specific needs and preferences, and it might be worth experimenting to see how it affects your equipment and your perception of tone.

The EU harmonization of voltage was indeed more about legal alignment than actual change in supply. Most UK homes still get around 240V, and European homes around 220V. If you install a device to regulate voltage to a constant 220V, amps designed for 220V might perform more consistently, potentially improving tone. However, UK amps designed for 240V could see a slight change in performance.

hubert