Originally Posted by Chula Vista

Everyone knows what a transformer does, right? You put a certain level of voltage in one end and can then get various different levels of voltage out of the other end. In the case of a tube guitar amplifier you plug it into the wall so that one end of the transformer sees 110-120 volts. That's way too much voltage for tubes and other components so the transformer steps it down to the appropriate amounts needed.

One of the most critical aspects of a transformer is the steel core. Different grades of steel will have different points at which they begin to saturate - distort, and not in a desirable way like say a distortion pedal. First thing to happen when the steel saturates is the low end impedance goes up and your low end tone starts to fart out.

Eddie discovered this by accident early on by experimenting with a variac and finding out that his 100 watt Marshall head sounded much better with only ~90 volts going into it instead of the 110-120 volts coming out of the wall. The transformer was no longer saturating. Voila! His legendary "brown sound".

One of the first things a transformer manufacturer will do to reduce theirs costs is to switch over to lower grades of steel which is often times very hard to detect. The changes in tone are very slight, especially if you play with lots of overdrive and effects.

TLDR: We talked about how to do QC tests to insure that transformers are consistent and the same as the approved standard.

Originally Posted by J.R.R. Tolkien

There is only one bright spot and that is the growing habit of disgruntled men of dynamiting factories and power-stations; I hope that, encouraged now as ‘patriotism’, may remain a habit! But it won’t do any good, if it is not universal.