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Blown fuse and its soldering to a PCB

I need competent advice:

I purchased a new amplifier (Dared MP-60, made in China). It is cheap and rather good sounding, but its left side got dead (left-side tubes stopped glowing) when I replaced the stock 5881 tubes with RFT EL-34 (everything was OK for 30 min. but next morning, when I was switching it on, the problem appeared), though it was permitted by the user manual and was authorized by the seller.

When I opened the cover, I saw four 125V 8A fuses covered with opaque plastic cases. The fuses have leads soldered to the PCB. We measured them and indeed one was blown.

What is strange that the seller says "you can use unsoldered fuse, but there is no place to place a unsoldered fuse on the PCB". I asked for explanations ("Does it mean that the whole PCB must be changed or that the unsoldered fuse should be replaced by another fuse which should be soldered to the PCB?, and she said "Yes, there is no place to place the unsoldered fuse on the PCB, it means the whole PCB must be changed".

Is this PCB a single-use dummy (if it is possible in principle)? How can it be that the blown fuse must be unsoldered but the new fuse cannot be soldered to the same place in the PCB?
transl
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stonedeaf
101 posts
 
When I serviced this stuff -always hated this.If it is possible -I would solder in fuse holders instead.BEFORE you do this -look at both sides of the board - is this going to even come close to touching another trace or component if you add holders? Something? blew this fuse - new tubes are definitely suspect - will be a real PIA if you solder a new fuse in and have to do it again in the next 2 min. or 2 days.I'm personally more than willing to desolder and solder components on a board BUT - pcb's are not really designed with this capability in mind.If you do this enough at one point on a board -you will pretty certainly have problems - the worst being the creation of a cracked intermittent foil trace.
Basically -if it's under warranty -I would return it for service and include the tubes you were trying to use.If the fault was caused by the tube - the importer will quit possibly charge you for the repairs.
timrhu
2,779 posts
 
Basically -if it's under warranty -I would return it for service and include the tubes you were trying to use.If the fault was caused by the tube - the importer will quit possibly charge you for the repairs.
Now that's good advice. I forgot we were discussing a new piece. Something I rarely own.
transl OP
156 posts
 
Given that the shipping cost was $270....+ $270 back with the amplifier price being $492...I'd rather repair it locally... I talked to a technician and he said that it's betteer to solder the leads to the fuse holder. I'll get the fuse first and then will try to figure it out.
transl OP
156 posts
 
Stonedeaf:

I don't believe the RFT EL-34 tube was a suspect - this set worked properly with Cary SLI-80 and another manually biased integrated amp. My technician insists that an auto-bias function may create problems when installing vintage tubes...
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stonedeaf
101 posts
 
Final note: Most service depts. will stock what are commonly referred to as "pigtail" fuses - these come from the factory with the wire already soldered to the end caps - much easier to use than trying to solder to the fuse without overheating it and blowing it before you ever get it installed.
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