Match the fuse that came out. Do not fit a larger one because a 2.5 A fuse opened. On this Sony HP-510A the speaker fuses are the 32 mm American size. A 5 by 20 mm fuse, which is what the first DigiKey part was, will not sit in the clips.
Both speaker fuses on this unit were intact when the right channel was crackling, so a fuse was not that fault. Spares still belong in the drawer before the first power-up after any transistor work. The order for that power-up is the dim bulb tester, then these fuses.
Read the fuse before you match it
| What you see | Buy | Do not buy | Shop |
|---|---|---|---|
| 32 mm long, cap says 2.5 A, element is one straight wire | Bussmann AGC-2-1/2, fast-blow 3AG | A 5x20 mm fuse, or any higher amp | View 32 mm long, cap says 2.5 A, element is one straight wire (affiliate) |
| Cap says T2.5A, or the element is a coil or a blob | A 3AG time-delay of that same amp | This fast-blow AGC | — |
| The two speaker fuses do not match each other | The SAMS list, Photofact MHF-44 | Whichever one looks newer | — |
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What was on the bench
The first candidate was an OptiFuse FSD-2.5A. Right amps, wrong body: 5 by 20 mm. The fuse in the holder is 32 mm. The Bel Fuse 3AG 2.5-R from DigiKey is that length, 2.5 A, fast-blow.
There is a small upside-down triangle near the marking that looks like it holds a T. That is not the time-delay prefix. Time-delay is the letters T2.5A printed in a row. The check that settles it is the wire you can see through the glass.
Look for a second fuse near the power cord. It is often a different amp, and it is often the time-delay one. Order that number separately. A fuse that blows a second time, with the rating matched, means stop. The bulb on the dim bulb tester is what keeps that short from taking the outputs.