FUSE Question...Very Confused Please Help !

@rocky1313 The 250V thing is an arc-over rating and nothing else.

For US operation you'll want the higher amperage rating as opposed to overseas operation.

Typical line voltage spec is ±5%. 110 x 1.05 ≈ 115. 

120v has been the US standard since 1967 🙄

120 * 1.05 = 126. 

126 volts is  ≈30% power increase into 110v transformer resistance [which will increase a little from excess power dissipation]

Check your mains voltage and get written certification from the manufacturer that the unit is 120v nominal rated. Insurance companies can be sticklers.

@ieales 

The amplifier is designed in Germany.  EU has 230V AC mains power. As stated the amplifier is made to be fed by 230V or 110V. The odd thing, at least to me, is the 110V mains feed. Not sure how the designer arrived at 110/230V.

Usually for a dual primary voltage power transformer there are two primary windings. Example 115V/230V.

The specs for the amp says it has a Max 500VA power consumption. If we assume the 500VA, is for the power transformer VA rating for the AC mains rated voltage(s), then each of the two primary windings are rated for 250VA at 115V each.

For 115V mains feed the two windings are wired in a parallel.

(2 paralleled 250VA windings = 500VA / 115V = 4.35A) 

For 230V mains the windings are wired in series.

(250VA + 250VA = 500VA / 230V = 2.2A.

Just a word about the amp's 250V fuse holder. Because the amp is designed to be fed from 230V mains the minimum fuse holder than can be used is the standard size 250V. So beings the same fuse holder is used also for 110V then naturally the fuse would have to be a 250 volt fuse to fit the fuse holder properly. 

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Thanks all for your responses, IT help me alot,