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Do fuses make a noise when they blow?

S

Supa Scoopa

Nov 23, 2007
190
2
Hobart, Australia
#1
My Marshall JCM800 keeps blowing fuses, it started today. Not sure whats causing it, but each time the fuse goes it makes a crackling sound (not from the speakers) and then a really weird smell. Is this what normally happens when you blow a fuse or is it something else going with it.

I have searched.
 
#8
Hi.

First of all, JCM800 is not a particular amp or a cab or even a combo. It's the Marshall line to follow JTM and JMP. The XXXX number, 1959, 2303, 1992 etc. is the model number.

Supa Scoopa said:
It's all good guys, I'm gonna take it to a tech on monday. Probably the output transformer he says.
Click to expand...

Good call, tech time is always advisable when something blows. Epecially when ever there's smell/smoke/sparks/flames involved.

However, I wouldn't say the most likely cause is the OT, but a shorted (output) tube. Fortunately there's a user friendly and a safe way to test whether the tubes are the most likely culprit or not.

Just mark the location of each tube ON THE BASE, NOT ON THE GLASS and gently remove each. The power tubes have to be removed as a set, the pre-amp tubes can be pulled individually to pinpoint the troubleshooting.

If the fuse(s) doesn't blow with all the tubes removed or just the pre-amp tubes installed, the power tubes or the OT are the most likely causes of the malfunction, the tubes being more likely. IME anyway.

Regards
Sam
 
#11
T-Bird said:
Hi.

First of all, JCM800 is not a particular amp or a cab or even a combo. It's the Marshall line to follow JTM and JMP. The XXXX number, 1959, 2303, 1992 etc. is the model number.



Good call, tech time is always advisable when something blows. Epecially when ever there's smell/smoke/sparks/flames involved.

However, I wouldn't say the most likely cause is the OT, but a shorted (output) tube. Fortunately there's a user friendly and a safe way to test whether the tubes are the most likely culprit or not.

Just mark the location of each tube ON THE BASE, NOT ON THE GLASS and gently remove each. The power tubes have to be removed as a set, the pre-amp tubes can be pulled individually to pinpoint the troubleshooting.

If the fuse(s) doesn't blow with all the tubes removed or just the pre-amp tubes installed, the power tubes or the OT are the most likely causes of the malfunction, the tubes being more likely. IME anyway.

Regards
Sam
Click to expand...
agreed. it could also be a rectifier tube. my fender super reverb's rec tube went out on me recently. usually they last forever but now and then they do go. so i'd do your test, but i'd try it with just the rec tube in there before proceeding to the power tubes.
 
#14
^ This. In rare occasions fuses may fail by themselves for no apparent reason, or at least without any reason relating to amplifier fault. But if after a fuse failure the replacement fuse fails as well then it's because the amplifier is damaged and fuses are doing their job. BUT the job of fuses is not so much protecting your amp is it is preventing hazards caused by heat effect of high current flow, that is hazards like component meltdowns or even house fires. So, throwing in fuse after fuse, while hoping the problem miracly fixes itself, is pretty much just pouring gasoline to the fire: from each moment you power up the amp to following fuse failure the fault gets to do further damage inside the amp. The noises and smell are a symptom of that; something's frying or arcing inside and something is burning or melting.

Take it to a tech.
 
#15
Hi.

Jim C said:
Sam, why can't you write on the glass?
Click to expand...

With correct ink, You can. Writing and labeling the base, and the base only has been the standard advice for as long as I can remember.

5881's, etc. and pre-amp tube markings have to be written on glass, obviously. There's tales of incorrect ink and even fingerprints shattering the glass, but in the 25 years I've been around tubes, I haven't personally witnessed such a thing to happen.
I do wipe the glass after installing, and I don't write on the glass though. Just in case ;).

And then there's the people who insist on using duct tape or painters tape for the labels... Perfectly safe they say.

Regards
Sam
 
#16
I was thinking a Sharpie marker
Ironically, there are a 1/2 dozen 12ax7's on the dining room table that I wanted to either date code or add a note about performance; have not done this before adn was regretting thinks like tube test data
Think that this potential to shatter glass would only be applied to power tubes?
Never heard this theory before but who knows?
 
#17
A (mechanical) crackling sound on a high voltage product along with a fuse that blows usually points to a failure of the high voltage insulating system (tube socket, wiring, output or power transformer) and should be serviced ASAP. Continuingto replace fuses will likely increase the amount of damage.
 

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