I recently bought a UK version of the Hafler IRIS preamp to replace my dead IRIS preamp. I just rewired the supply to change the unit over to USA current. It was working beautifully. I added my IRIS tuner to the chain and after I plugged that into the preamp switched outlet the preamp went dark and quiet.
I found the preamp internal power fuse was blown. I replaced it with the fuse from my original USA preamp. And still nothing. A test with my DMM showed the replacement fuse was open. The sticker inside my old USA IRIS preamp states "use only direct replacement 3/16A 125 slow-blow MDL/3AG".
The two bad fuses don't match the sticker, and they don't match each other:
UK fuse: 1/10A 250V 313 (resistor inside it)
USA fuse: 3/16A 250V 313
So is this a 3 amp fuse? A 16 amp fuse?
How do I find the correct fuse? The big online vendors are no help at all.
I've been searching Mouser, Digikey and Newark for an hour, and I can't find anything with "3/16A" in the search fields. Oddly, if I do a web search for "MDL 3/16" I can find a reference to that type of fuse in the Eaton docs, but the fuse shows up as "obsolete". I found an updated version on their site, and searching for that part number via DDG takes me to a Digikey page for that very fuse, which can't be found by using their online search tool!
I've had trouble using these search engines before, especially when trying to find capacitors. If anyone could please explain to me the right way to search for this fuse I'd appreciate it.
I found the preamp internal power fuse was blown. I replaced it with the fuse from my original USA preamp. And still nothing. A test with my DMM showed the replacement fuse was open. The sticker inside my old USA IRIS preamp states "use only direct replacement 3/16A 125 slow-blow MDL/3AG".
The two bad fuses don't match the sticker, and they don't match each other:
UK fuse: 1/10A 250V 313 (resistor inside it)
USA fuse: 3/16A 250V 313
So is this a 3 amp fuse? A 16 amp fuse?
How do I find the correct fuse? The big online vendors are no help at all.
I've been searching Mouser, Digikey and Newark for an hour, and I can't find anything with "3/16A" in the search fields. Oddly, if I do a web search for "MDL 3/16" I can find a reference to that type of fuse in the Eaton docs, but the fuse shows up as "obsolete". I found an updated version on their site, and searching for that part number via DDG takes me to a Digikey page for that very fuse, which can't be found by using their online search tool!
I've had trouble using these search engines before, especially when trying to find capacitors. If anyone could please explain to me the right way to search for this fuse I'd appreciate it.
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For a preamp I would guess 1A Time Delay (anti surge) for UK 240V and 3A Time Delay for USA voltage.
Remember the power drawn will be the same whether on 240 or 115 but the current will be much lower on 240V.
Your comment on 'resistor inside' is a bit puzzling 🙂
Remember the power drawn will be the same whether on 240 or 115 but the current will be much lower on 240V.
Your comment on 'resistor inside' is a bit puzzling 🙂
There is a resistor inside the glass cartridge. I've never seen that before.
So the 3 in the "3/16A" refers to 3amp, slo-blo? What does the "16A" refer to then?
I can't say I've come across fuses with that marking on them or tbh ever had to delve that deep. Could it be the surge rating over x number of cycles?
Resistor... do you mean it looks like this. If its something totally different then maybe a picture would help.
Resistor... do you mean it looks like this. If its something totally different then maybe a picture would help.
Attachments
Its not totally different - replace that coil with a carbon resistor, that's what I have here.
Well it would figure that both of the fuses I have here bear little to no resemblance to that table.
The exact markings I have on each fuse-
UK fuse: 1/10A 250V 313
USA fuse: 3/16A 250V 313
There are no markings visible on the rest of the fuse, other than "LF" and "UL" on the ends. Manufacturer and certification marks. Nothing else.
That sounds very odd.
The coil in the image I posted is actually a spring and used to cleanly pull the blown fuse wire part cleanly away should that eventuality happen.
So yours has a carbon resistor visible in the glass cartridge?
Maybe we could do with seeing a good detailed picture of this part... I just can't visualise it tbh.
That said, if it all worked OK until you connected an external load to the switched outlet then it sounds just like a 'normal' kind of fuse.
It's going to be tomorrow before I look in again but I'm intrigued... and a good picture will help, also maybe one of its location in the unit as well... and hopefully someone else will probably pick this up and be able to identify it from that.
The coil in the image I posted is actually a spring and used to cleanly pull the blown fuse wire part cleanly away should that eventuality happen.
So yours has a carbon resistor visible in the glass cartridge?
Maybe we could do with seeing a good detailed picture of this part... I just can't visualise it tbh.
That said, if it all worked OK until you connected an external load to the switched outlet then it sounds just like a 'normal' kind of fuse.
It's going to be tomorrow before I look in again but I'm intrigued... and a good picture will help, also maybe one of its location in the unit as well... and hopefully someone else will probably pick this up and be able to identify it from that.
I'll do that. But in the meantime, that's not the fuse I'm trying to replace. I need to get that USA value fuse I mentioned above. Can you give me some pointers to finding that?
USA fuse: 3/16A 250V 313
It is a 3/16A (0.1875A) fuse.
In such small values it is hard to get a clean slow-blow action. I have seen sub-sub-Watt resistors inside to provide a cheap repeatable heating delay.
Mouser Part # 576-0313.187MXP
Mouser Part # 504-MDL-3-16-R
> I just rewired the supply to change the unit over to USA current. .... I added my IRIS tuner to the chain and after I plugged that into the preamp switched outlet the preamp went dark and quiet.
You did the "change over" wrong. I can't see it from here.
In such small values it is hard to get a clean slow-blow action. I have seen sub-sub-Watt resistors inside to provide a cheap repeatable heating delay.
Mouser Part # 576-0313.187MXP
Mouser Part # 504-MDL-3-16-R
> I just rewired the supply to change the unit over to USA current. .... I added my IRIS tuner to the chain and after I plugged that into the preamp switched outlet the preamp went dark and quiet.
You did the "change over" wrong. I can't see it from here.
I just found this:
Resistor inside a fuse? | Electronics Forums
@PRR thanks, I've never come across fuses rated that way in the UK/EU
Resistor inside a fuse? | Electronics Forums
@PRR thanks, I've never come across fuses rated that way in the UK/EU
Attachments
I just found the exact resistor thats was inside my USA preamp:
313 Series Slow Blow Type Fuses-3/16 Amps - 95998 | LawsonProducts.com
The pic may be a "representative image" but it happens to look exactly like what I have here on my desk. Unfortunately, its discontinued. The replacement seems identical, but where the old one was "Slow Blow Type" the new one states "Time Delay". Are those equivalent or is there a difference?
313 Series Slow Blow Type Fuses-3/16 Amps - 95998 | LawsonProducts.com
The pic may be a "representative image" but it happens to look exactly like what I have here on my desk. Unfortunately, its discontinued. The replacement seems identical, but where the old one was "Slow Blow Type" the new one states "Time Delay". Are those equivalent or is there a difference?
Just to add that any fuse for supplying a transformer is normally Anti Surge... now over here our nearest common value would be a T200ma
its a new one on me. I've never seen anything like that before in any equipment I've ever come across.I'll look in tomorrow, you're in good hands with PRR.
Yes, and use the original fuse type and rating to prevent a fire hazard.
Consider the possibility that at this age these fuses are blowing for a reason, namely that components in the pre-amp are failing and causing the fuse to blow.
The unit should probably have all of its electrolytic capacitors replaced, and be gone through for other defects.
I was going to say OMG, but PRR set the record straight before any harm was done. (Thanks PRR!)
Consider the possibility that at this age these fuses are blowing for a reason, namely that components in the pre-amp are failing and causing the fuse to blow.
The unit should probably have all of its electrolytic capacitors replaced, and be gone through for other defects.
I was going to say OMG, but PRR set the record straight before any harm was done. (Thanks PRR!)
I'll look in tomorrow, you're in good hands with PRR.
They are common here in very low current applications where the fuse action needs to be delayed.
Yes, thats why I posted the question, so I'd be sure to buy the exact right fuse.
I agree that is a possibility. However, the preamp worked perfectly and the only thing that changed is that I rewired the transformer for USA current without replacing the UK value fuse. The USA fuse is 3/16A, the UK fuse is 1/10 or roughly half the value of the USA fuse. Plugging the tuner into the switched power on the preamp might have been too much for that fuse. I'll start with replacing the fuse and see what's next.
I completely agree, and the perfectionist in me says to replace all the caps and the voltage regulators and whatnot. Then I recalled the wisdom of a person who has about 30 years in the hifi service business; he told me, "Repair any problem before you start upgrading things".
The proper first step was to check the fuse, and that turned out to be bad. Once thats replaced I'll see what happens next.
I don't understand what you mean.