Hey all,

I have a Blockhead 100w that keeps blowing the main 3amp fuse.

Could an overdrive pedal cause the amp to get pushed too hard and then blow the fuse?

Or maybe the tubes too old?
I've had them about a year and play out twice a week.

Thanks
Bill

hey Bill,
How long does it take to blow the fuse?? If it blows right away or fairly quickly then try this.
Usually the main culprit is the power tube(s)if the amp has been running fine and you know the tubes are old.
Insert a new fuse, then remove the power tubes. If the fuse still blows then we will go from there. Lets hope its the tubes :-)
Don't run the amp for a long time without the tubes in it though.

Best of luck~!!

I had an amp do this and my bass player had an amp do this too. My amp had something blown in the rectifier circuit. My bass player though had a blown transformer....hopefully it's something simple like power tubes or in the rectifier circuit like mine. My bass players new transformer is going to cost him a bundle.

The overdrive pedal wouldn't do this, as the output of the preamp tube will is limited by its own clipping. It is probably one of the tubes. It could, however, be a transformer starting to go. It may be that as the output transformer is heating up, its electrical characteristics start to change from thermal drift and thus, it starts to pull too much current. Try yanking out the preamp tubes and letting the thing run for about 5 minutes longer than it usually takes for it to pop a fuse. If the problem goes away, then it may be one of the preamp tubes is partially shorted. If it doesn't go away, try replacing the preamp tubes and running it without the power tubes for the same amount of time. If this doesn't work, try disconnecting the center tap of the output transformer from the power rail. If this doesn't work, reconnect this and put the tubes back in. At this point, get a tech to look at it. It may be the power transformer is going. Oh, it could also be arcing in the tube sockets. Check to see if you have carbon burns on any of them. And make sure that the tube pins on the inside aren't able to brush one another. It may be that as you play, the vibration is ratting a couple of these into each other.

If new tubes doesn't cure the problem I would let an experienced tech check the amp. For one thing there are lethal voltages inside there and another reason is that it is a very expensive amp with custom transformers. You could risk increasing the repair cost if you short out the wrong part.

Just my $.02 but I am an electronics tech and I know something about it.

You can never have too many toys

Rectifier circuit failure or OT tranny issues.

Bb

Have you tried replacing with a 5 amp fuse?

I kid.

quote:

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Originally posted by ceterisparibus:
Have you tried replacing with a 5 amp fuse?

I kid.

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5 amp? just wrap the blown one in tin foil (seriously don't do this)

I had a similar problem a few years ago and it was a bum power tube.

Emailed the guys at Blockhead. Ozzie said to just replace the 3 amp fuse with a 5 amp fuse. At first I was concerned about doing this, but he assured me that it wouldn't hurt anything.

After replacing the main 3 amp fuse with a 5 amp fuse, it works just fine.

Thanks yall.

Hey Bill,
while I have no doubt the guys at Blockhead know what they are doing I still have to say that you should try some new tubes. Something caused the amp to keep blowing fuses and if the amp came with a 3 amp fuse then it shouldn't blow it unless a problem exists. The 5 amp fuse may work fine but it also may be letting tooo much current to parts that may fail due to the larger fuse. Fuses don't blow for no reason and I would hate to see the amp blow up on you.

I would call the guys at Blockhead and ask for some tech info for the amp/tubes to see where they are biased and check the voltages in the amp.
I also have to add that tubes don't last as long nowadays. If you have had them in the amp for a year and play out twice a week you should change them anyway. Also after a year of working those tubes you should check the bias voltages anyway. As the tubes wear they don't always carry the same voltage as when they were new.

Well there is my $.02 as well.

I hope everything works out for you Bill.

Peace
NUKLHED

Are you using a slo-blo fuse? My fender amp specifies those types to be used, otherwise they burn out also.

Bill,

there is a bunch of good info right here in the replies, at least 4-5 possible reasons why the 3 amp fuse is blowin. I know you moved to a 5 amp fuse but I would still be a little cautious. I had a Hiwatt 100 doing the same thing for over a year and finally i gave up and took it to my valve amp guru. Somebody else on here hit the nail on the head in my sceanrio. It was the tube sockets. In my absence some beer got spilled into the top heat vent of the head and i was not informed of this (go figure right? So what ended up happening was that the sugar from the dried up beer had coated the power tube pin sockets and would blow the 3 amp fuse religiously after the amp got warmed up. My tech installed porcelin sockets and it has worked fine for the last ten years, same fuse no problems. You might take a look at he sockets and at least clean them or look for carbon burn marks like the earlier poster described. The rectifiers and transformers are very expensive to repair/replace and that can be painful. good luck ... lots of good info here on these posts!!! cheers