Fuses keep blowing out in Dual Rectifier Head

[Schizo]

Hello, the fuse on my Mesa Dual Rectifier solo head is blowing out every time I push the standby switch to ON position. The amp powers on properly but I already tried with 3 fuses by now in consecutive failure cause every time I turn the standby switch into ON position the fuse blows up! The amp is 1.5 years old and so are the tubes. I checked the tubes, they were lighting properly when I turn the Power ON, even I left them in standby mode for almost 10mins, they were still lighting properly and then I tried to turn on the standby switch but the fuse blows up Please help me finding what could be the problem. I live in Bangladesh and there's no proper tech. here to fix mesa amp heads.

Thanks

 

[scottieL]

sounds like some kind of short. sucks that you can't even get it to stay on long enough for a tube test. If it's 1.5 years old, it'll be under warranty. so take it to a mesa service center or just back to where u got it and have them sort it out.

 

[Schizo]

Sadly I don't have any mesa service center in my country, I live in Bangladesh and bought the amp from Bangkok, Thailand. ****, its getting tough for me, thanks for the advice anyways.

Does anyone else know about the problem please?

 

[fluff191]

you have a direct-to-ground short SOMEWHERE. That much is for sure. Also make sure you are using SLO-BLO fuses. Not Fast-BLO.

 

[thunda1216]

ditto on the slo-blo's. Try replacing the rectifier tube. They can develop shorts but still light up.

ty

 

[boxcarmonument]

I recently had the same problem. And my tubes looked fine. But looks can be deceiving. It was a tube problem for me that was causing my fuses to blow. Even though my tubes were glowing fine and looked Ok. Since it started blowing fuses Has your tone changed? When I replaced a blown fuse with a good one, My amp sounded like ***. So take that into consideration.


Good luck,
Dave

 

[anttman7788]

I know you said you checked the tubes, but i had the same exact problem the day after i bought my used triple rec. I knew nothing about tube amps and blew about 7 fuses. so I went in head first. I did some research and replaced all the power tubes and since my amp has worked perfectly. I would say give that a try. I got 6 new jj tubes for $100 so it aint that pricey. Give it a try

 

[mikey383]

ditto on the slo-blo's. Try replacing the rectifier tube. They can develop shorts but still light up.

ty

Not the problem. If the head powers on at all, the rectifier tube isn't the culprit.

You have a bad power tube. Case closed. Replace the power tubes and the fuse, then try again.

For future reference, if the fuse blows, replace it and power the head on (leave in standby). If it blows, a rectifier tube is bad. Replace. If the fuse doesn't blow upon power up but blows upon taking the amp out of standby, a power tube is bad. Power tubes can look good, but that does not mean they are.

Also, when a power tube blows, it's a safe bet to take it to a tech and have it checked out. A screen resistor is a common thing to need replaced after a power tube failure.

 

[fluff191]

Once again Mikey is dead on.

I had the same symptoms when my power tube blew. And thank goodness I can replace anything that might be destroyed as well.

 

[Avoletfo]

Ok, so I'm no amp expert, but I've been researching my issue and can't figure it out. I was playing my amp, sounded normal and then it went dead. I've had it for 4 years gigging aggressivley and no issues whatsoever. So I check, blown fuse... Radioshack, pack of 4 fuses. Replace fuse, and as soon as I turn the power on it blows. Pull and visually inspect all tubes and pots, nothing jumps out at me. Replace power tubes and fuse still blowes when I flip the switch on. Pull all (except the preamp) tubes and still, the fuse blows when I power it up. Nothing "looks" bad, nothing smells burnt, but no luck. I don't trust anyone in my local area to work on this thing. Any other thoughts on what it could be??? Thanks ahead of time for the help.

-Rob

 

[mansfieldguitars]

One more neat trick for troubleshooting blown fuses is to use a current limiter. You can easily make one of these for a few bucks. The idea is to place a 100 watt light bulb in series with the power cord. When you first tuen the amp on the light should glow bright but then dim down. If the light stays bright then there is a short of some kind however since the 100 watt light bulb is in series it limits the current thus you won't blow the fuse. You can then troubleshoot the same way by pulling tubes one at a time and so forth. Just watch the light bulb. When you pull a tube and the light dims, you found the culprit. If anyone wants to no more about the current limiter I can post pics and a schematic. One can be made easily for $10.00 to $20.00.

John

 

[shinodax]

I got this problem previously as well. I took the advice from mikey and replaced 1 rectifier tube and it's done! =)

 

[droptrd]

Thats sounds interesting. Please tell

One more neat trick for troubleshooting blown fuses is to use a current limiter. You can easily make one of these for a few bucks. The idea is to place a 100 watt light bulb in series with the power cord. When you first tuen the amp on the light should glow bright but then dim down. If the light stays bright then there is a short of some kind however since the 100 watt light bulb is in series it limits the current thus you won't blow the fuse. You can then troubleshoot the same way by pulling tubes one at a time and so forth. Just watch the light bulb. When you pull a tube and the light dims, you found the culprit. If anyone wants to no more about the current limiter I can post pics and a schematic. One can be made easily for $10.00 to $20.00.

John

 

[Metaghius]

One more neat trick for troubleshooting blown fuses is to use a current limiter. You can easily make one of these for a few bucks. The idea is to place a 100 watt light bulb in series with the power cord. When you first tuen the amp on the light should glow bright but then dim down. If the light stays bright then there is a short of some kind however since the 100 watt light bulb is in series it limits the current thus you won't blow the fuse. You can then troubleshoot the same way by pulling tubes one at a time and so forth. Just watch the light bulb. When you pull a tube and the light dims, you found the culprit. If anyone wants to no more about the current limiter I can post pics and a schematic. One can be made easily for $10.00 to $20.00.

John

would be interested in seeing the schematic and pics please.

 

[94Tremoverb]

Simplest: get any old power extension cord, and *carefully* open up the outer sheath halfway along its length, making sure you don't damage the plastic insulation on the inner cores. Now cut the white or black wire - it doesn't matter which, but only cut *one* of them - and connect the two ends to a standard lamp holder. (Blue or brown wire in Europe.) This is safe enough - just keep your hands away from the holder while it's in use.

As to why the amps are blowing fuses, it's been covered already but just to make it totally clear: 90% or more of the time, if a fuse blows it's a bad power tube or rectifier tube. If the fuses blows immediately on power up with the standby engaged (amp muted) it's a rectifier tube. If the fuse only blows when switching out of standby, it's a power tube. Bad preamp tubes don't blow fuses.

Also for reference, it's almost always safe to test an amp with no power tubes in it, and always safe with no rectifier (although it may not tell you where the fault is, because with the rectifier out the power tubes may not work either, in a non Dual rectifier), but *don't* pull all the preamp tubes and power up. This is maybe counter-intuitive, but running an amp with no preamp tubes in can risk damaging it, due to voltage rise at the far end of the filter cap chain. Pulling the power tubes only raises the voltage by a few volts.