Problem after biasing my friend's Herbert...

  • Thread starter Thread starter defpearlpilot
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defpearlpilot

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I was biasing the amp, the last pair actually, and as I powered it on, I heard a pop. After that when I turn on the power nothing lights up. I do see that one of the fuses is blown, but even if I remove it, like I would to bias, it doesn't light up. Did I damage the amp? The multimeter doesn't read any current across where the fuse was. This sucks!
 
Have You checked the main fuse underneath the power cord? There, on the little "drawer", should be a replacement fuse as well.

If the mains' fuse is OK, as far as I know, there should be couple fuses located in the board within the amp from which at least another is related to the power tubes. Thus, in order to be able to reach these fuses you need to open up the amp and turn it upside down on a table (Careful with the tubes! Lay the amp resting on its output transformers on e.g. pile of books). If you are uncertain what you are doing PLEASE do ask someone more qualified with electronics to do it in order not to cause any fatal injuries to yourself or to your beloved amp.
 
i.ak":7f470 said:
Have You checked the main fuse underneath the power cord? There, on the little "drawer", should be a replacement fuse as well.

If the mains' fuse is OK, as far as I know, there should be couple fuses located in the board within the amp from which at least another is related to the power tubes. Thus, in order to be able to reach these fuses you need to open up the amp and turn it upside down on a table (Careful with the tubes! Lay the amp resting on its output transformers on e.g. pile of books). If you are uncertain what you are doing PLEASE do ask someone more qualified with electronics to do it in order not to cause any fatal injuries to yourself or to your beloved amp.
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Well, I biased my own Herbert a couple of times before. So I figured it would be no problem biasing a friend's. I think the main fuse is the problem. I was looking for another one but couldn't find it.

BTW, do you know what kind of fuses these are? rating?
 
Hi Andrew, there's a spare mains fuse in the fuse holder (jack).

Those are 5x20mm euro-sized fuses (smaller than those typical Marshall things), rated 4A minimum, slo blo.
 
duesentrieb":da28d said:
Hi Andrew, there's a spare mains fuse in the fuse holder (jack).

Those are 5x20mm euro-sized fuses (smaller than those typical Marshall things), rated 4A minimum, slo blo.
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Thanks to both of you. I checked this morning under the jack and there was a blown fuse there! What a relief! Hopefully they have these fuses at GC or Sam Ash.
 
If you're blowing main fuses, I'd be careful about just replacing it and re-powering. I did precisely that with my VH4, and the actual issue was a shorted power tube, which apparently caused some damage when I re-powered with a new fuse. Of course, YMMV.
 
Just had a look at the back of my Herbert. 120V = 6.5 A Slo Blo.
 
madhouse":1ba23 said:
If you're blowing main fuses, I'd be careful about just replacing it and re-powering. I did precisely that with my VH4, and the actual issue was a shorted power tube, which apparently caused some damage when I re-powered with a new fuse. Of course, YMMV.
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Hmm, I fear you may be right. I keep blowing more fuses. I'll have to send it to a tech as I don't have a tester. This sucks.
 
Maybe one of the new power tubes is bad.
Pull the tubes and replace the fuse.
If the amp don´t blow the fuse You have
found the fault.
 
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