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amp broken? help!

snakeman1986

Member
Messages
243
Ok guys i just tried to plug my vox ac15c1 in the power outlet and didn't realize my amp had both the power on and stand by switch on. It popped and fizzed and then went dead silent. No hiss or buzz no matter how high i turn up the power. Can someone diagnose my problem?
 

snakeman1986

Member
Messages
243
That's awesome. I'm far from an amp tech so i was freaking out. This makes perfect sense though. Hopefully it won't be hard to find one around here. I don't know anything about fuses. thanks for the help guys
 

snakeman1986

Member
Messages
243
One thing that still concerns me is the fuse that blew was not the one by the power cord. It is one of them on the board.



Should i expect any problems once i actully get another fuse in that spot?
 
Messages
602
Quickest way to find out. Replace the fuse (with one of the same rating) and turn the amp on correctly. If it blows the fuse again, you've got a problem. If not, it was likely just a result of the awkward power-up.
 

snakeman1986

Member
Messages
243
Quickest way to find out. Replace the fuse (with one of the same rating) and turn the amp on correctly. If it blows the fuse again, you've got a problem. If not, it was likely just a result of the awkward power-up.
Ya that's the plan. Just a little worried because i need the amp for Wednesday, Thursday, Saturday and Sunday. Bad week for this to happen...
 

PBC

Member
Messages
607
That's awesome. I'm far from an amp tech so i was freaking out. This makes perfect sense though. Hopefully it won't be hard to find one around here. I don't know anything about fuses. thanks for the help guys

Saying you don't already know this, look on the side of the fuse for its power rating and match that (10A, 15A etc.) be sure to get the proper fuse type as well (slow vs, fast blow). These are available at all electronics stores and a lot of gas stations as well. I keep an extra couple of them taped to the inside panels of all my amps as a just in case measure. As it was mentioned earlier it likely blew because the circuit was overloaded at start up so the fuse did was it was supposed to do, interupt the current flow to protect the more valuable circuits in the chain after the fuse.
 

StompBoxBlues

Member
Messages
20,115
Saying you don't already know this, look on the side of the fuse for its power rating and match that (10A, 15A etc.) be sure to get the proper fuse type as well (slow vs, fast blow). These are available at all electronics stores and a lot of gas stations as well. I keep an extra couple of them taped to the inside panels of all my amps as a just in case measure. As it was mentioned earlier it likely blew because the circuit was overloaded at start up so the fuse did was it was supposed to do, interupt the current flow to protect the more valuable circuits in the chain after the fuse.
That was nice of you to check, I was going to do the same.
Just to mention too, when you buy fuses (especially when one has blown) always buy at least 5, even better 10. ONLY replace (as mentioned above) with the exact same amp rating,voltage rating, and type (Slo-Blo, or regular).

Five is minimum. If there is a problem, you blow fuse number one. You may want to try a small thing or two, but there may go fuse number 2, three left..etc. You can quickly go through a number of them...and they aren't expensive.
 

snakeman1986

Member
Messages
243
Ok cool. Thanks everyone. I don't know anything about fuses so this is all great info for me. I am hoping to go to radioshack on my lunch break. Surely they have some.
 

Kyle B

Silver Supporting Member
Messages
5,109
A new fuse isn't likely to fix your problem.

Get a new fuse, pull all the tubes, and plug it in. See if the fuse blows again. If it does, Stop now - you need to go to a tech. If it doesn't, unplug, wait several minutes for high-voltage to drain away, put in first tube. If fuse doesn't blow, repeat. If you find a tube which makes the fuse blow, you need to replace that tube.


BTW - I looked in Radio Shack online catalog. They don't appear to carry a 5x20mm 250mA Time delay (SloBlo) fuse. DO NOT SUBSTITUTE. Order a dozen from Digikey if you have to
 
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HawkeyeKane

Member
Messages
1,325
Well i called my radioshack in town and i guess I'm lucky because they have 20 of them.
Take your blown one in with you and make sure they are a dead match. I've gotten to RS before after calling about things like this, only to find what they told me they have wasn't what I really needed.
 

snakeman1986

Member
Messages
243
I was looking at radio shack online and found a 250mA 250v fuse but it says fast acting. I'm guessing this wouldnt work on this case. I need slo blow right? What's the difference?
 

Kyle B

Silver Supporting Member
Messages
5,109
Its the time delay characteristic. Basically how long the fuse can maintain the 'break' current before it pops. This time is measured in milliseconds -- It's not a big difference on human timescales, but it could mean the difference between melted circuit boards and a blown fuse.

The reason you need a 'slo blow' is because of the amps internal capacitors. When you first fire up the amp, these caps are completely empty. There's a sudden inrush of current as they fill up with juice. Once topped off, the current supply is reduced to a trickle.

If you use a fast-blow, it will probably pop during the inrush current stage. You won't damage anything, but you'll be blowing fuses for no reason. You need a slo-blow in virtually any type of amplifier application.
 

snakeman1986

Member
Messages
243
Great...I've called 9 or 10 places in town. None carry a 250mA fuse. They have a 200, 500 and even a 315 mA but no 250mA. Crazy.
 
Messages
602
Well, I think you've already got the idea that you shouldn't substitute a fuse with different characteristics in there, but just as a bot of education-
There are two reasons not to.
The first has already been mentioned - if you use an underrated fuse, it will pop even if the amp is working properly, so you're just wasting fuses.
The second is that, if there is a problem with the amp, and you sub in an overrated fuse, the fuse won't blow when the problem presents itself, won't protect the rest of the circuit from whatever the fault condition is, and you'll end up damaging an expensive part of the amp.

And now you know everything you need to know about fuses.
 

Kyle B

Silver Supporting Member
Messages
5,109
Great...I've called 9 or 10 places in town. None carry a 250mA fuse. They have a 200, 500 and even a 315 mA but no 250mA. Crazy.
If you're too impatient to wait for mailorder, the 200mA slo blow will probably work fine.

A dirty little secret from us electronics engineers --- we just kinda guess at the right value for a fuse, and keep putting in smaller ones until they start to pop. Then back off and say "use this one" :) Not anywhere near as much "science" behind the selection as you might think :tapedshut
 






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