Why does my amp keep blowing it's fuse?

[johnjm22]

My Mesa Boogie Single Recto blew its fuse today, so I replaced it with another, which proceeded to blow right after I took the amp off stand by. So then I replaced the fuse again and recieved the same result; another blow out.

Am I doing something wrong? Why would my amp be doing this?

[dementedchord]

try googling.... SHORT cause youve got one.....whatever you dont just put in a bigger one.... time to see the doctor...

[Geoff_T]

Originally Posted by johnjm22

My Mesa Boogie Single Recto blew its fuse today, so I replaced it with another, which proceeded to blow right after I took the amp off stand by. So then I replaced the fuse again and recieved the same result; another blow out.

Am I doing something wrong? Why would my amp be doing this?

Hi

What were you doing immediately prior to it blowing a fuse?

Did the room lights change in brightness?

[johnjm22]

Originally Posted by Geoff_T

Hi

What were you doing immediately prior to it blowing a fuse?

Did the room lights change in brightness?

Thanks for the reply.

I turn on the amp in standy by mode, wait for about a minute to let it warm up, then I flip the switch from stand by mode to playing mode.

As soon as I flip the switch the fuse blows. It happened three times in a row.

The lights in the room did not change.

[Geoff_T]

Originally Posted by johnjm22

Thanks for the reply.

I turn on the amp in standy by mode, wait for about a minute to let it warm up, then I flip the switch from stand by mode to playing mode.

As soon as I flip the switch the fuse blows. It happened three times in a row.

The lights in the room did not change.

Hi

I was trying to figure what would cause the fuse to blow the first time. Now the damage is done, it will continue to blow fuses until the cause of the short circuit is removed.

Are you sure you can't remember what was going on when the fuse blew the first time? Like unplugging a speaker load or something?

Whatever, it needs to be checked over by someone that understands the beast.

[johnjm22]

Originally Posted by Geoff_T

Hi

I was trying to figure what would cause the fuse to blow the first time. Now the damage is done, it will continue to blow fuses until the cause of the short circuit is removed.

Are you sure you can't remember what was going on when the fuse blew the first time? Like unplugging a speaker load or something?

Whatever, it needs to be checked over by someone that understands the beast.

Just prior to the fuse blowing the 1st time the amp was plugged into a bad outlet. My freind was shaking the power cord to get the amp to work. I could see the LED light on the front of the amp flickering on and off.

I figured that's what caused the fuse to blow. I didn't know it could cause other problems.

[Geoff_T]

Originally Posted by johnjm22

Just prior to the fuse blowing the 1st time the amp was plugged into a bad outlet. My friend was shaking the power cord to get the amp to work. I could see the LED light on the front of the amp flickering on and off.

I figured that's what caused the fuse to blow. I didn't know it could cause other problems.

Hi

Now you can see why I kept questioning you as to what you did prior to wrecking it!

"Shaking the power cord to get it to work".... Oh my Lord, there should be a law against such silly behaviour!

Think about it one moment... by shaking that cord you were switching the thing on and off repetitively... and where transformers are involved you can get surges and back emf from such tricks... and you have messed up the amp in the process.

The amp needs to go to a repair shop... your place needs a qualified electrician to check the power outlets and tighten up any loose screws.

You have just enrolled in the school of hard knocks.

[johnjm22]

Thanks.

I need to learn more about electronics.

[00420]

Originally Posted by johnjm22

Thanks.

I need to learn more about electronics.

Hey, at least you didn't try to solve the problem by replacing the fuse with a fuse rated for a higher amperage

That's more than can be said for some people.

[johnjm22]

Originally Posted by 00420

Hey, at least you didn't try to solve the problem by replacing the fuse with a fuse rated for a higher amperage

That's more than can be said for some people.

I feel better about myself already.

[brianroth]

Or worse yet, wrap the blown fuse with a piece of metalized paper from a stick of chewing gum. I call that a "Wrigley's 100 Amp No-Blow fuse".

Bri

[Matt Syson]

While the answers above are good and correct, you should make sure you are actually replacing it with the correct type of fuse. If it calls for an anti-surge type (Usually has a T written on the rating plate) it will need a T rated fuse otherwise it will blow when switched on. I looked at a Mesaboogie a while ago which was blowing 7 amp fuses virtually straight off each time. The correct antisurge 'fixed' it!
NEVER use a bigger fuse than rated, it gets expensive! If fuses are blowing then it is a cry for help so get it checked out properly.
Matt S

[Mixermend]

The clue here is that the fuse blows when the Standby switch is operated.

It sound like you have a short circuit on the HT supply after the standby switch.....

Could also be that the rectifier valve(s) - are defective.

Don't waste yet another fuse - but I bet that the rectifier valves flash when the switch is thrown!

Could also be the output valves - but as previous advice - time to seek knowledgeable assistance now.

[tmarra]

Pull all the output tubes, switch it on and see if the fuse holds. If all's well then put in one output tube at a time until it blows. More than likley it's a output tube.

Switch it to solid state rectifier and you can rule out the any of the tube rectifiers, or just remove them also.

If it still blows after removing the rectifiers and output tubes, take it to a tech.

-Tony

[DeeDrive]

Originally Posted by tmarra

Pull all the output tubes, switch it on and see if the fuse holds. If all's well then put in one output tube at a time until it blows. More than likley it's a output tube.

Switch it to solid state rectifier and you can rule out the any of the tube rectifiers, or just remove them also.

If it still blows after removing the rectifiers and output tubes, take it to a tech.

-Tony

I agree, my experience with tube amps has been, when you start blowing fuses, your power tubes are generally shot and need to be replaced. If one of them is shorted, it will blow fuses every time. Taking it to a tube amp tech is your only real option.

[2leod]

Originally Posted by brianroth

Or worse yet, wrap the blown fuse with a piece of metalized paper from a stick of chewing gum. I call that a "Wrigley's 100 Amp No-Blow fuse".

Bri

So you're saying this is a no-no?
Dang! - Cross that one off my list of handy MacGyver tricks.

I must admit that on Sunday I had the main fuse in one of my guitar amps jumpered with a piece of solder trying to verify that the puff of smoke wafting from the the back was indeed one of the electrolytic caps. Not the smartest thing I've ever done... Remember kids, don't do this at home, electricity kills!

[Matt Syson]

hi
If you are playing this game how about putting a mains lightbulb in series with your equipment while testing. If you have a short, the light comes on. You could even have a selection of bulb ratings for 'degrees of nervousness'.
Cheap, cheerful and possibly safer than a variac (used within it's limitations).
Matt S