Originally Posted by REVPOWER
Fuse direction matters. The difference is usually discernable without trying to listen too hard.
When inserted the wrong way, the sound will usually be a bit flatter and softer. Imaging not as good. It can still sound OK, just not "right".
On fuses with directional arrows - you should still experiment. Unless you are a circuit designer or tech, you may not know the true direction of flow in the circuit. Some boards have been known to be marked incorrectly.
In testing marked fuses here, it's been determined that the fuse manufacturers are marking them correctly for directionality.
Method to check correct installation directionality without being a Tech: Unplug AC cord, remove fuse. Using any cheap multi-tester set to resistance in ohms, connect one lead to to one of the two non-ground blades inside the IEC connector on your component that your AC cord's female connector plugs into. using the other lead, touch one of the sides of the fuse holder. Keep trying the combos, four in all (two IEC non-ground blades, two fuse holder sides) until resistance is zero; Three combos will show high resistance; one will show no resistance. The one with virtually no resistance is, of course, the side of the fuse holder into which the current flows from the IEC. That is the side of the holder that one will place the starting part of the IsoClean arrow or the HiFiTuning diode symbol (direction-wise, looks like an arrow anyway) such that the current flows in the same direction as the arrow. I cannot speak with certainty about the Furutech (writing from left to right, current from left to right?)
The above test can also be done with a continuity test on better multi-testers, my cheapo does not have one, but the resistance test is equal to it. Continuity simply means no resistance. The high resistance of the three high-resistance combos is because there is all that circuitry of the component beyond the other side of the fuse holder! The no-resistance side is simply directly connected to one side of the inlet IEC connector.
If you don't have a multitester, I advise getting one from say, Radio Shack, for almost nothing. A serviceable one costs less than a fuse! They are handy things to have anyhow!
Hope this helps.