Blew a fuse

cobascis · Post by **cobascis** » Sun Jul 25, 2010 7:12 pm

So I was playing through my Bassman when the light went out. No sound. Turned it on, off, on. Waited 4 hours, etc. No change. I took the fuse out and it is clearly blown(?). Hardware stores sell fuses, correct? Anyway it says 250V 2.5A, should I be able to find a direct replacement? And I understand there are slow-blow fuses and other kinds...

Shaguar · Post by **Shaguar** » Sun Jul 25, 2010 7:29 pm

Just bring it to the store with you and ask the salesman.

Will · Post by **Will** » Sun Jul 25, 2010 7:34 pm

Hardware stores and such still have them. And yes, you want SLO-Blow so it doesn't break when the tube filaments first turn on.

Check your power tubes as well - something made that fuse blow.

cobascis · Post by **cobascis** » Sun Jul 25, 2010 7:38 pm

Will wrote:Hardware stores and such still have them. And yes, you want SLO-Blow so it doesn't break when the tube filaments first turn on.

Check your power tubes as well - something made that fuse blow.

I had new JJs put in and biased professionally a few months ago.

Billy3000 · Post by **Billy3000** » Sun Jul 25, 2010 8:18 pm

Will wrote:Hardware stores and such still have them. And yes, you want SLO-Blow so it doesn't break when the tube filaments first turn on.

Check your power tubes as well - something made that fuse blow.

The only times I've ever blown fuses it's been because of a power surge. It's not necessarily because of a tube problem.

With older amps, I would recommend checking the caps though. My guitar player's '79 Marshall JMP was blowing fuses and it just turned out to be some bad caps.

cobascis · Post by **cobascis** » Sun Jul 25, 2010 8:51 pm

Billy3000 wrote:
Will wrote:Hardware stores and such still have them. And yes, you want SLO-Blow so it doesn't break when the tube filaments first turn on.

Check your power tubes as well - something made that fuse blow.
The only times I've ever blown fuses it's been because of a power surge. It's not necessarily because of a tube problem.

With older amps, I would recommend checking the caps though. My guitar player's '79 Marshall JMP was blowing fuses and it just turned out to be some bad caps.

Already been recapped, but it was plugged into a surge protector, and nothing else that was plugged in got hit.

Will · Post by **Will** » Sun Jul 25, 2010 9:59 pm

6L6s can blow fuses sometimes if vibration causes the plates inside the tube to touch or get too close together and arc.

It can happen with any tube, but most often in 6L6s cause there are 7 big, heavy plates crammed inside.

There's also something just called fuse fatigue - if it's an old fuse, that's probably the culprit.

cobascis · Post by **cobascis** » Sun Jul 25, 2010 10:15 pm

Will wrote:6L6s can blow fuses sometimes if vibration causes the plates inside the tube to touch or get too close together and arc.

It can happen with any tube, but most often in 6L6s cause there are 7 big, heavy plates crammed inside.

There's also something just called fuse fatigue - if it's an old fuse, that's probably the culprit.

40+ years old, so that is likely.

Thanks.

cobascis · Post by **cobascis** » Mon Jul 26, 2010 6:03 pm

Bad news folks. Tried 2 different 2.5a fuses, both blew instantly, then I tried 2 amp slo blo ( printed on amp ) it booted up but emitted a terrible screeching sound and I saw one power tube light up with sparks inside. Fucks sake,".

George · Post by **George** » Mon Jul 26, 2010 6:05 pm

40+ year old tubes? Jeez mang.

Billy3000 · Post by **Billy3000** » Mon Jul 26, 2010 6:13 pm

You said you just got all the tubes changed out right? It's possible that it wasn't biased correctly or you just got a bad tube. Regardless, take it to a tech before doing anything else yourself. If you keep trying fuses and blowing fuses you can run the risk of damaging your transformers which will be much more costly to repair than tubes.

cobascis · Post by **cobascis** » Mon Jul 26, 2010 6:26 pm

GeorgeF wrote:40+ year old tubes? Jeez mang.

1 month old tubes. Old fuse

Will · Post by **Will** » Mon Jul 26, 2010 8:15 pm

Sounds like the plates inside the tubes got close or touched - it happens with 6L6s. One of the costs of getting 25W of power from a smallish tube.

If you can afford it, might want to swing by a tech and have them look to see that there are no loose wires in the chassis. Otherwise just pop in some new tubes. You shouldn't need to bias 6L6s in a bassman.

cobascis · Post by **cobascis** » Mon Jul 26, 2010 8:22 pm

Will wrote:Sounds like the plates inside the tubes got close or touched - it happens with 6L6s. One of the costs of getting 25W of power from a smallish tube.

If you can afford it, might want to swing by a tech and have them look to see that there are no loose wires in the chassis. Otherwise just pop in some new tubes. You shouldn't need to bias 6L6s in a bassman.

Email from my the said the power tube sparked, and he'd look for problems when putting em in

Sloan · Post by **Sloan** » Thu Aug 05, 2010 12:08 am

take the power tubes out and try to power it up without them, you won't hurt anything, but if the fuse stays good, then you know it's most likely a tube prob.

laterallateral · Post by **laterallateral** » Thu Aug 05, 2010 12:29 am

I had something very similar to this happen to me after a particularly bumpy van ride to a venue with my YBA-1...
Mine has a circuit breaker and not a fuse but no matter what I did, the breaker would trip after taking the amp off of standby and the whole thing would power right down. It'd be totally fine when idling, though...

Turns out my problem was that the tip of an ancient TRS cable that must have broken off inside an input, had rolled under the turret board and was shorting something out. I fixed (and diagnosed) this problem by simply turning my amp upside down.

You'd probably have to take the chassis out of your Bassman to do this but you might wanna give that a try cause christ knows how much time and money I would have sunk changing caps and tubes before I figured out what the problem was, otherwise.

Just saying, this is probably not a common issue and must admit I'd be more than a little surprised, if this turned out to be what your problem is, but... What have you got to lose?