Blowing Amp Fuses!

[John Price]

Hello,

So my 2 channel c amp just blew a fuse! It was one of the main fuses that are located in the slot with the power chord.I pulled it out and found a matching replacement fuse and that one also blew on me. I looked at the manual and back of the amp both indicate to use 3 amp 250 volt, but when I checked the blown fuse and the other fuse in the slot, both of them are marked as 2amp. Could this be the problem? I just brought this one home Yesterday.....

 

[Danerada]

Yes it could. I would get the 3 amp fuse if that is what it calls for. I had an amp that was blowing fuses and it turned out to be a problem with the trasformer...

 

[Em7]

An amp that blows fuses the moment one applies power has a short. I would start by checking the power tubes for an internal short.

Power Tube Short Test Procedure

1.) With the amp off, pull the power tubes
2.) Install a new properly-rated fuse
3.) Apply power and take the amp off of standby

If the amp blows another fuse, the problem is more than likely in the power supply. If the amp does not blow a fuse, install a new pair of power tubes and reapply power. If the amp blows a fuse, you more than likely have a short in the output transformer. If the amp does not blow a fuse, you will need to bias the power tubes before using the amp. If the amp runs for a while before blowing a fuse after biasing the power tubes, one of the screen grid resistors may be out of spec.

You need to ensure that you are using "slow-blow" fuses. Slow-blow fuses are designed to handle the inductive surge that occurs when one applies power to a tube amp.

One last thing: it helps to have access to an autotransformer (a.k.a. a variac) that has built-in voltage and current meters when testing for shorts. A metered autotransformer allows one to monitor current draw as one raises the supply voltage. I built my metered autotransformer.

 

[Shawn@PRS]

Hi John,

If you would, please take the amp back to your dealer and ask them to call PRS. We'll issue a Return Authorization number for the amp and have it brought back to the factory for a repair. Once the work has been done, we can ship it directly to you or back to the dealer, it's your call.

I'm sorry for he inconvenience.

Shawn

 

[John Price]

Thanks for all the replies!
All the info was greatly appreciated.

I was able to get the proper 3 amp slow blow fuses and put them into the amp. Fired right up for me. I'm hoping that this was the cause of the problem.

Thanks again for the great replies.
John

PS: I don't why I'm not receiving a replied email to this thread when I'm already subscribed...?