Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Will a 1.6amp 250v fuse work safely in place of a 1.6a rated at 100-117v?

Yes

They did not have that size...2a 250v should be alright?

The voltage rating of a fuse is what it is rated to withstand once it has blown open.  This mainly has to do with the internal spacing, so a fuse rated for a higher voltage will generally work just fine on a lower voltage.

The current rating is the same no matter what the operating voltage.

The basic consideration with any fuse is the implicit power, so a 2 amp fuse will blow in a 110 volt circuit when 2 * 110 = 220 watts is being drawn by the load, and in a 240V circuit when 2 * 240 = 480 watts is being drawn (and this is determined by the circuit voltage, not the fuse voltage rating).

The key question in any fusing is if the fuse will actually blow under fault conditions - will the circuit allow a blowing current to flow?  This is mainly important when fusing the primary of a power transformer because the transformer itself will limit the primary current to some value if there is a short on the secondary, such as a shorted rectifier.  If a short on the secondary won't draw enough current in the primary to blow the fuse in use then the tranny itself will simply cook until it too fails and draws a high fault current.  This is mainly a concern with small transformers.

Increasing a fuse from 1.6 to 2 amps generally speaking will be okay, but there may be some situations, say with a small transformer, or when the original fuse specification was a bit too generous, where you may get a non-blowing problem.  One way to test this is to fit a much higher value, say 5 amps, and momentarily short the transformer secondary while measuring the primary current, and fitting a fuse that is higher than the highest expected service current, but lower than the momentary short value measured.

HTH

Thanks, I thought I was on track...Been 12 years since doing any electronics theory so I'm rusty. I figured the xtra 400mA would be ok, but you are right, If they were generous with the rating in could just cook the PS xformer.