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Fuses For Small Amps....slow-blow Or Quick-blow?


djhollowman
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Hey all,

I have recently been helping a fella with his amp. It's a Marshall 15w combo. He says it kept cutting out, then went permanently dead. I checked the plug fuse...OK, checked the speaker...OK, checked the glass fuse on the PCB....dead. I've replaced it with another one, which made me realise I need to buy more fuses of the same rating, but do I need slow-blow or quick-blow ones?

On a side note, having inserted the replacement fuse, the amp no longer cuts out, but it only wants to make noise when the master volume is turned up to 10!! Now, I realise it's only 15w but it's bloody loud at 10, and the pot is acting more like a switch than a gradual change! Any ideas? The pot isn't scratchy. I know Marshalls wanna run at 10 all the time, but this is ridiculous!! :D Apparently it didn't do that before it died.

DJ

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Not sure what the master volume quirkiness is about, but on tube amps, they usually use a slo-blo fuse so they can handle the inrush current of the tube filmaments without blowing right away.

Edited by Paul Marossy
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The pot is probably broken and only making contact at the end of its rotation. Pots do funny things when they break.

As to the fuse... I'm guessing this is a solid-state amp, in which case I don't know. But I agree with Paul, tube amps generally use slo-blow.

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The pot is probably broken and only making contact at the end of its rotation. Pots do funny things when they break.

As to the fuse... I'm guessing this is a solid-state amp, in which case I don't know. But I agree with Paul, tube amps generally use slo-blow.

Its slow blow in both solid and valve they both produce spikes during switch on don't know why maybe capacitors loading or something fancy like that. god i need sleep.

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Not sure what the master volume quirkiness is about, but on tube amps, they usually use a slo-blo fuse so they can handle the inrush current of the tube filmaments without blowing right away.

That's what I kinda suspected, thank you!

The pot is probably broken and only making contact at the end of its rotation. Pots do funny things when they break.

Hmm, it's possible yes. So, if that was the case, I'd just have to unsolder the pot, source a suitable replacement and fit it?

DJ

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Not sure what the master volume quirkiness is about, but on tube amps, they usually use a slo-blo fuse so they can handle the inrush current of the tube filmaments without blowing right away.

That's what I kinda suspected, thank you!

The pot is probably broken and only making contact at the end of its rotation. Pots do funny things when they break.

Hmm, it's possible yes. So, if that was the case, I'd just have to unsolder the pot, source a suitable replacement and fit it?

DJ

Yes.

How many of the pots leads are being used? 2 or all 3? Guessing all three and that the wiper isn't making contact until it touches one of the end contacts.

But with solid state amps, things sometimes get funny after a power spike. There might be more wrong than just the pot. After all, something made the fuse blow . . .

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After all, something made the fuse blow . . .

That's right... you gotta find the root problem, or you'll just keep blowing fuses.

Look over the PCB for burn marks, goo, melted stuff, broken connections, etc.

I hate troubleshooting amps. :D

its not that hard...

if it causes trouble shoot it!

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