So, why *do* fuses blow?

[CoG]

I was just reading about rabies' hassles with his new Stiletto, and thought I'd ask. I blew a fuse on Saturday in my 20/20 (only a few months old.) It had been on standby for about 10 minutes, I turned it on, started playing, and then things got real quiet about two minutes in. :roll:

I'm plugged into a power conditioner, so in theory I shouldn't have gotten hit with a surge.

All four power tubes appear to be working just fine, so I didn't blow a tube.

My knowledge of fuses ends there, unfortunately. Why else might it have gone?

Seem to be a surprising number of "reliability" threads lately...

 

[Murphy Slaw]

I blew a fuse on a Peavey Deuce in 1982 in a club in a Louisiana swamp. My beer fell over and when the cold beer rolled down the back and hit the 6L6's that had been on for 3+ hours, the drummer, who was behind the amp got a light show he'll never forget. The tubes literally exploded, and the fuse blew.

Replaced the tubes, and the fuse, and finished the night.

Sorry I can't help, but that just reminded me of how funny that was.

Best of luck.

 

[phyrexia]

Just because a tube looks like it's working doesn't mean there's not a short in it. When a tube shorts it pulls too much juice, and it pops the fuse.

 

[CoG]

thanks guys!

Just because a tube looks like it's working doesn't mean there's not a short in it. When a tube shorts it pulls too much juice, and it pops the fuse.

and I guess it's possible for this to happen w/o the tube being immediately damaged? I popped in a new fuse an hour later and everything seems happy, I've played about ten hours since then with no problems. I'd just be happier having an idea of why it blew.

 

[azazelsmight]

I blew many fuses in my first hours with my Triple Rec. :evil:

 

[CoG]

the fuse blows to protect the rest of the circuit from damage. your situation is illogical unless it was a bad fuse???

well, yeah, that's what I figured... it didn't make sense to me either unless either the fuse was bad or the power conditioner isn't working as advertised.

 

[alongcameandroo]

so do any of you change fuses regularly as a preventative measure? do they wear out? is it better to put a new fuse in about once every 1 or 2 months?

 

[JerryFJA]

Fuses don't go bad or fail on their own. A fuse is here as a protection device to prevent major damage or fire when something shorts inside an amp. 99% of the time blown fuse are caused by a shorted power tube or rectifier tube.
When a fuse blows find out why, don't just keep throwing fuses in the amp, that's is not a repair. While many times the shorted tube could be an intermittent thing and a new fuse will work for a while, it will fail again. Everytime the fuse blows you're putting undue stress on the amp.
When a fuse blows find the problem and fix it. It was NEVER just a bad fuse.
Jerry

 

[CoG]

When a fuse blows find the problem and fix it. It was NEVER just a bad fuse.
Jerry

Well, that's just it. All my power tubes still seem to be working just fine, and there's no rectifier tubes in a 20/20, so I'm stumped.

Would you suggest changing out all four power tubes just on spec that one of them may be shorting?

I have no idea how to test my power conditioner...

 

[chedgeco]

When a fuse blows find the problem and fix it. It was NEVER just a bad fuse.
Jerry

Well, that's just it. All my power tubes still seem to be working just fine, and there's no rectifier tubes in a 20/20, so I'm stumped.

Would you suggest changing out all four power tubes just on spec that one of them may be shorting?

I have no idea how to test my power conditioner...

Jerry's right... replace the tubes. Intermittent means it will fail again and it will most likely happen when you least want it too.

If they are Mesa tubes, give them a call and explain to them what happened. They will most likely do right by you.

Chris

 

[JerryFJA]

EL84's are horrible power tubes and they fail much more often than the big boys. Change them. The JJ's seem to hold up the best these days. EL84's are notorious for making jingly rattling noises, pops, crackles, and blowing fuses. That's the trade off for a nice break up at low volumes.
Jerry

 

[Rocky]

EL84's are my fav power tube, I havent had issues like described above. In 20+ years of driving them hard I can count the issues that I have had on one hand.

 

[JerryFJA]

EL84's are my fav power tube, I havent had issues like described above. In 20+ years of driving them hard I can count the issues that I have had on one hand.

Consider yourself lucky! The EL84 was never designed to run as hard as it does in a guitar amp so they don't hold up well. They were designed for car radios.
Jerry

 

[CoG]

Well, this gives me an excuse to try some new tubes anyway