Variac vs. Isolation vs. Balanced Transformer? ALL

I posted a similar question about 6 months ago on Audiogon, in reference to a high voltage problem I have at my location. I have been using an older tube amp that was not designed to run on higher voltages, and my lines are giving me a pretty consistent 124 volts. The voltages inside my amp run beyond the ratings on power supply caps. and other components, which can cause premature failures.
I needed to reduce my line voltage in order to extend the life of the amp, and tried a variac as the first affordable solution. I tried a good quality 10 amp unit, but unfortunately, it degraded the sound. I did not have the budget for some of the more expensive $1000+ line conditioners that could also regulate voltage, so I tried the following suggestion I had from a fellow Audiogon member: http://www.geocities.com/jonrisch/catch2.htm
It is a D.I.Y. high current transformer that can reduce output voltage AND be configured to output balanced power as well. It is a Signal DU-2 transformer, which can be purchased new for a bit over $300. I got mine on the used market for under $100 (E-Bay). I made my own enclosure for it, and wired it with a high quality AC outlet and power cord to the wall. I am now getting a constant 113 Volts for my tube amp, with the benefits of cleaner, balanced power. It works like a charm, and throws off very little heat and no hum. After re-biasing my tube amp for the lower voltage it puts out, it sounds fantastic with no loss of dynamics, and with a slightly deeper and more detailed soundstage. My amp runs cooler and all the new power supply caps, signal caps and other components installed from a recent re-build should last for decades.... Problem solved, and for well under $150!

Yes, a dedicated line is the first step, a good outlet, properly treated room, and correct speaker placement are often the least costly "tweaks" that all add up.
I am using the Signal DU-2 transformer. It is rated at 2Kv and 18 amps as an isolation transformer, and about half that when wired to produce balanced power. Mine ran warm and made an audible hum when wired as an isolation transformer. I did not notice any gains in sound quality running the amp through it this way, but it did reduce the voltage. When I wired it balanced, it runs extremely cool with no audible hum. There was a noticeable change for the better in detail and soundstage, but it was not not quite as dramatic as my previous BPT 3.5 Ultra power conditioner I was running. It sure was a LOT less money though, and my tube amp should last me a long time.
I can send you a diagram showing how to wire it if needed. It is not as difficult as you would think. It only took me an hour or so...

Mine had no wires coming off of it, just screw terminals with nuts to wire your primaries and secondaries to. You can just do a search for Signal DU-2 transformer and you will find some electronics dealers that either stock or order them for you. Last time I checked, new ones were around $350 plus another $50 for shipping. There is a smaller Signal DU-1 on E-Bay right now for around $150, and a HUGE Signal DU-10 (10kva) unit for $900+ ( this thing weighs 175lbs!). If you wait a while, you can find a used DU-2 on there for a sane price. If you view the picture of the big Signal DU-10 on there, my DU-2 looks very similar to it, but a smaller 65lb version.