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Understanding Ceramic Fuses ...

mzeitlin3348

mzeitlin3348

See it and Believe
I woke up this morning - went to turn on my preamp/stereo system - nothing.
I looked at the pre-amp and it is stone cold - no power whatsoever.

So I took the cover off and checked the fuse first. It is a Bussmann Ceramic 250V 1.25 MDA. I assume this is a slow blow 1.25 amp fuse.

I checked with my ohm meter and sure enough it had a lot of resistance.

I did not have a spare fuse so I decided to put in another ceramic I had laying around with a lower rating: 250V 0.5A (not a Bussmann) just to see if something is blowing the fuse.

I put the fuse in and my system came back to life playing music as before.

My question is can I just leave it this way? or do I need to find an exact replacement fuse and not use my pre-amp until I get it properly fused? And why did the original fuse blow in the first place? Can they just wear out? The pre-amp is 11 years old and original.
 
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I would guess that at the very least, the current handling of 1 1/4 amps should be used. A half amp fuse probably won't last very long.

As for wearing out, nothing lasts forever, so a fuse giving out after 11 years seems like a reasonable possiblity. You might want to check out your preamp just to be sure.
 
I agree it likely won't last as long or do any harm but whats puzzling is why it would blow when the amp wasn't turned on.
 
yamafan said:
I agree it likely won't last as long or do any harm but whats puzzling is why it would blow when the amp wasn't turned on.
Click to expand...

It probably blew on power up :scratch2:

Fuses fatigue and wear out, so can blow for no reason - but usually they DO blow for a reason.
 
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yamafan said:
I agree it likely won't last as long or do any harm but whats puzzling is why it would blow when the amp wasn't turned on.
Click to expand...

This is a Krell pre-amp. There is no on/off power switch. The unit is "on" all of the time (although in Standby). The power button in the front activates the speaker connects and status indicator lights and controls the connected power amplifier. So even when the pre-amp is "off", the heat sinks/metal case are quite warm to the touch - and stay that way. It is a feature of the unit.

I replaced the Bussman 1.25 MDA ceramic fuse with an ABC 0.5 ceramic fuse temporarily. I understand that MDA (OEM from the unit) is time delay and ABC is fast acting.
So is it o.k. to replace the MDA fuse with an ABC until I can get the proper MDA fuse? Why time delay anyway? When current exceeds the rated amount - wouldn't you want the fuse to open to protect the device? Just curious.
 
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mzeitlin3348 said:
This is a Krell pre-amp. There is no on/off power switch. The unit is "on" all of the time (although in Standby). The power button in the front activates the speaker connects and status indicator lights and controls the connected power amplifier. So even when the pre-amp is "off", the heat sinks/metal case are quite warm to the touch - and stay that way. It is a feature of the unit.

I replaced the Bussman 1.25 MDA ceramic fuse with an ABC 0.5 ceramic fuse temporarily. I understand that MDA (OEM from the unit) is time delay and ABC is fast acting.
So is it o.k. to replace the MDA fuse with an ABC until I can get the proper MDA fuse? Why time delay anyway? When current exceeds the rated amount - wouldn't you want the fuse to open to protect the device? Just curious.
Click to expand...

Time delay or slo-blo on the AC side is for start up " inrush surge" of the power transformer.
 
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