Replacing a fuse for a beginner

[ParkerLudwig]

Hey all, first post here. I just got an old JCM2000 DSL401 (Clean-OD1-OD2, 4x EL84, Marshall Gold Back speaker) combo from my drummer. He said that the amp turns on, but no sound comes out, so I could keep it and try to fix it if I wanted to. I figure at the very least I could try and salvage the cabinet and speaker for my other amps, but if possible I'd like to get it working since I've played various eras of the DSL amps and have liked them.
I tested the speaker with my Valvestate VS100H head, and the speaker works perfectly fine. The dust cap is peeling off, but it's useable for now. Not opposed to a speaker upgrade later. The main point though is that the amp lights turn on, the switches work, none of the pots feel loose or broken, but there's obviously no output. I tried every single volume, gain, and tone control. I tried going straight into the effects loop, as well as with a preamp. I tried using the emulated line out, thinking it might be a power amp issue. Nothing. All of the tubes still glow. I know it's not the safest, but I checked each one with my hand after a few minutes and it felt like a pretty standard temperature for a working tube amp. Pretty hot, but not alarmingly so.
I took out the HT fuse and tested for continuity, and got nothing. I took out the mains fuse (which I knew worked, but just to make sure I did it right), and that one gave me a signal. So I'm fairly confident that I can at least try a new HT fuse and go from there. They seem fairly cheap, and all of the other things seem to indicate that the amp would work. I'm just asking if there's any general advice for changing a fuse. I have basic pedal electronics knowledge but amplifiers are still very new to me so I'd rather ask than hurt myself or the amp.
On the back panel, right next to the fuse it says "T400mA". I assume I need a 400mA fuse, but which brands do you recommend? If I can't find exactly 400mA, would something like 500mA be suitable (the Marshall website sells 0.5A and 630mA, but no 400mA)? Are all 400mA fuses (or any fuse of any given measurement really) the same size? Is it fine to just go to a hardware store and find a fuse there, or do I need something specifically for guitar amps?
And finally, let's say the fuse is the issue, and I get the right replacement. Do I just change it out, power the amp up and use it as normal after that? Or is there anything I need to tweak before using it? I apologise for the absolute barrage of questions, I just figured I could ask some more knowledgeable people instead of sketchy Google searches for questions that don't match up with mine

 

[Jon Snell]

Always fit a like for like as this is a safety component.
You require a T400mA 250v fuse.
Do not buy from fleabay because you will not know the quality. Some 1Amp fuses from fleabay won't blow at 3Amps!
Shurter, Littlefuse etc are known good brands. Ceramic are expensive but extremely reliable and minimise any damage to the fuse holder in case of catastrophic issues.
I would suspect an output valve has caused the fuse to blow. A new set of output valves may be a good option.
Don't know whether you require 20mm or 1 1/4" so here is a known good supplier for you to browse and gain information.

Cartridge Fuses | Glass Fuses | 13 Amp Fuses | RS

Browse our latest Cartridge Fuses offer. Place your order today for our Cartridge Fuses. Fast Delivery.

uk.rs-online.com

Hope that helps.

 

[Matthews Guitars]

Pull the power tubes out before installing the new fuse.

Then turn the amp on. If the amp powers up, good. Now turn it back off and reinstall the power tubes.

Now turn it on again. If it blows the fuse, you've likely got a bad power tube. (Or two.)

When you buy the fuse, buy several. A five pack at least.

Never think the fuse is the problem. It is a safety device. When it blows, it is telling you that there is something
else in the amp that is the problem.

 

[macanoodough]

So does the amp value of the fuse matter? What are the differences, if any, between the 1, 3 or whatever? I need one myself but I'm getting way too many options and want to buy the correct fuse the amp came with, if not a better option. I can't buy from the link posted because they don't ship out of Englandland.

 

[Dogs of Doom]

So does the amp value of the fuse matter? What are the differences, if any, between the 1, 3 or whatever? I need one myself but I'm getting way too many options and want to buy the correct fuse the amp came with, if not a better option. I can't buy from the link posted because they don't ship out of Englandland.

yes...

if you get too light of a fuse, it will constantly pop & you'll have to replace it. If you get too high of rated, it might not do it's job when something goes south, & things in the amp fry, as a consequence...

better to just get the proper fuse, as recommended by spec, & the mfgr.

What amp? & what does it say? Which fuse?

 

[paul-e-mann]

Hey all, first post here. I just got an old JCM2000 DSL401 (Clean-OD1-OD2, 4x EL84, Marshall Gold Back speaker) combo from my drummer. He said that the amp turns on, but no sound comes out, so I could keep it and try to fix it if I wanted to. I figure at the very least I could try and salvage the cabinet and speaker for my other amps, but if possible I'd like to get it working since I've played various eras of the DSL amps and have liked them.
I tested the speaker with my Valvestate VS100H head, and the speaker works perfectly fine. The dust cap is peeling off, but it's useable for now. Not opposed to a speaker upgrade later. The main point though is that the amp lights turn on, the switches work, none of the pots feel loose or broken, but there's obviously no output. I tried every single volume, gain, and tone control. I tried going straight into the effects loop, as well as with a preamp. I tried using the emulated line out, thinking it might be a power amp issue. Nothing. All of the tubes still glow. I know it's not the safest, but I checked each one with my hand after a few minutes and it felt like a pretty standard temperature for a working tube amp. Pretty hot, but not alarmingly so.
I took out the HT fuse and tested for continuity, and got nothing. I took out the mains fuse (which I knew worked, but just to make sure I did it right), and that one gave me a signal. So I'm fairly confident that I can at least try a new HT fuse and go from there. They seem fairly cheap, and all of the other things seem to indicate that the amp would work. I'm just asking if there's any general advice for changing a fuse. I have basic pedal electronics knowledge but amplifiers are still very new to me so I'd rather ask than hurt myself or the amp.
On the back panel, right next to the fuse it says "T400mA". I assume I need a 400mA fuse, but which brands do you recommend? If I can't find exactly 400mA, would something like 500mA be suitable (the Marshall website sells 0.5A and 630mA, but no 400mA)? Are all 400mA fuses (or any fuse of any given measurement really) the same size? Is it fine to just go to a hardware store and find a fuse there, or do I need something specifically for guitar amps?
And finally, let's say the fuse is the issue, and I get the right replacement. Do I just change it out, power the amp up and use it as normal after that? Or is there anything I need to tweak before using it? I apologise for the absolute barrage of questions, I just figured I could ask some more knowledgeable people instead of sketchy Google searches for questions that don't match up with mine

T means slow blow, make sure to get T400mA slow blow fuses. Never put anything other than what is printed on the amp. Pop it in and see what happens, if it blows again pull the power tubes and try again to see if it holds without them, if so get new power tubes. Not sure about this amp but you might have to set the bias.