Fast blow or slow blow fuse?

Borat

New Member
First I have to thank you guys for sharing your knowledge.

I initially came to this forum to ask about the possibility of converting my two MC275's voltage from 120V to 240V. Lots of members chipped in and told me that it's an easy thing to do - all I need to do is to switch a few tabs on the primary wirings of the transformer.

So I paid an electrician with over 20 years of experience of hi-fi repair to do the switch for me. He told me that he switched a few tabs of the primary wirings, and then tested his work by putting 220V through the primary wiring and then measure the output of the secondary wiring. Everything was looking good.

After I took the amp home, I went to Radioshack and bought some 2A fast-blow fuses. I switched out the original fuse which has a 4A rating (I don't know whether it's fast-blow or slow-blow)

But when I tried to start the amp by giving it 220V, the 2A fast-blow fuse blew immediately. A friend of mine told me that I shouldn't use a fast-blow fuse because the initial current surge would definitely blow it right away.

Does anyone know which fuse type is the right one to use? I must admit that the original 4A fuse supplied by Mac looks just like a fast-blow fuse. The slow-blow fuses I saw at Radioshack all have slightly thicker filaments. But my friends say some slow-blow fuse filaments are just as thin and it is difficult to tell the difference.
 
Borat.......I looked at a schematic I have on the original MC275. It shows F1 as a Slow-Blow fuse. The original MC275 calls for a 5A fuse at 105-130 volts, but that amp has a receptacle mounted on the amp that is powered through that fuse, as well as the amp. If your amp is labeled for a 4A fuse at 120 volts, the 2A slow-blow fuse at 240 volts should do the job.
 
Could I revive this thread? I also have an MC275, and have used fast-blo fuses because someone told me that I am less likely to damage the amp with a power surge, as the fuse will blow easily, and that there was no downside to a fast-blow fuse, other than the cost of replacing them from time to time. True?
 
The slow blow fuse is designed not to blow during the initial high current switch-on surge so I am very surprised if your fast blow fuses survive if they are the same rating as the slow blow - can I ask if you are using the same amp rating fast blow as you should slow blow ?
 
The slow blow fuse is designed not to blow during the initial high current switch-on surge so I am very surprised if your fast blow fuses survive if they are the same rating as the slow blow - can I ask if you are using the same amp rating fast blow as you should slow blow ?

Yes. The sticker above the fuse on the base of the MC275 says Slo-blo T5A 250V. So I have purchased regular 5A 250V fuses, and they seem to work ok, although I had a blow recently (nothing too violent - about 1/8" of filament was gone).
 
Normally I would advise you to replace your Quick-Blo fuses with Remington 22LR cartridges but with your switch to 240V it could get messy....
 
Hi, I have yamaha amplifier HTR-3065 USA model, using it in india. It has 125v 6A slow blow fuse which got blow away. So can I replaced with 250v 6A fast blow fuse or 250v 3A fast blow fuse?
(I couldn't find 125v 6A fuses in India)
 
Welcome to AKs McIntosh forum, we usually do not get Yamaha questions here though.

If you blew a fuse you need to find out why the fuse blew....a fuse is there to protect and most often they fail because something failed inside the unit. Replacing blown fuses without having a tech check out why the fuse went open could end up costing you much in repair costs as problems have a tendency to cascade.

The original question was about units designed and built in the USA for the USA market and being converted to use in Europe which runs on 240 volts not the 120 in the US.

Have you switched the voltage to 240 volts or are you using a step down transformer?

If you have switched the transformer to run on 240 in India..... a proper fuse would be 1/2 the USA rated amperage, 3 amps at 250 volts. If you are using a external step down transformer to feed it 120 a 6 amp 250 volt would be OK.
 
Welcome to AKs McIntosh forum, we usually do not get Yamaha questions here though.

If you blew a fuse you need to find out why the fuse blew....a fuse is there to protect and most often they fail because something failed inside the unit. Replacing blown fuses without having a tech check out why the fuse went open could end up costing you much in repair costs as problems have a tendency to cascade.

The original question was about units designed and built in the USA for the USA market and being converted to use in Europe which runs on 240 volts not the 120 in the US.

Have you switched the voltage to 240 volts or are you using a step down transformer?

If you have switched the transformer to run on 240 in India..... a proper fuse would be 1/2 the USA rated amperage, 3 amps at 250 volts. If you are using a external step down transformer to feed it 120 a 6 amp 250 volt would be OK.
I used step-down transformer. Can I go with 6A 250V Fast-bow fuse?
 
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