Fuse blowing on start up

T

timbro52

New member
This is my 3rd Bottlehead kit and i've made my share of goofy mistakes. But for the life of me I can't figure out what I have or haven't done this time (and no I'm not on crack, yet). Checked all my solder joints, resistance test is fine, but when I flip the switch I blow the fuse. Anyone out there with suggestions would be greatly appreciated.

Thanks,

Tim
 
If the above is not the problem recheck the direction of the diodes.  Then check the power supply capacitors and be certain the stripe is on the side indicated in the pictures.  Doc puts excellent pictures in his manuals. 
 
Thanks Doc and Grainger, 

I have the newer manual and the diodes are correct and the caps as well.
I guess I'll check all my solder joint again.
Thanks,

Tim
 
The fuse blowing indicates high current.  That could also be a short in the power supply.  Possibly a piece of wire that was cut landed in the wrong place. 

If you find nothing try pulling the tubes and then turning it on.  You can leave it on for a few seconds and then check the fuse. 
 
Thanks Grainger,

I'll give it a try. By power supply do you mean the transformer? If that's the case I don't see any lose, stray, or miss placed wires.
If the fuse doesn't blow with the tubes out where does that leave me? I realize this is a process of elimination but I'm a newbie to this stuff.
I'm out of fuses, so it's off to the hardware store.

Thanks again,

Tim
 
By power supply I mean the transformer (not likely), the diodes, the capacitors or the heater circuit.

If the fuse doesn't blow with the tubes out it indicates a problem around or in the tube.  It could be a shorted tube or a problem with the plate or cathode circuit.
 
Hello Tim, did you double check the orientation of the power supply capacitors?  How are the resistance checks?
 
I am wondering where can I get these fuses?
I had the first one ever blow (and it really really freaked me out for a bit....I couldn't figure out what happened!)  Still not sure really, other than I was plugging/unplugging/rearranging things and it must have been a result of that somehow.
I was able to rob a fuse from one of my DJ lights (250v, slightly lower rating though) and I went and bought what I thought were the right ones @ Radio Shack, only to find they are too big!  I guess they are 1.5" and I need 1"? 

Where is a common place to find the right ones?

I need to use my DJ lights this weekend...
 
Hi Dan,

My local Radio Shack has the right fuses on and off. I usually have to dig through the fuse drawer to find what I need.
Now days I stock up and buy them from Amazon (what don't they sell!). If you just search for slow blow fuses it brings up about 4 pages.
I have Amazon Prime so I can get stuff shipped "2 day" to me for almost nothing.
Sign up for the free trial for Prime and you'll get like me. I buy my socks, underwear, tennis shoes, computer stuff ,.. well, you get the idea.
Now, all I need to do is figure out where I put things like fuses.
 
what are the full specs I should be looking for?

It occurred to me that the fuse that came with mine may not be "stock".
 
Here's the ones from Amazon (I don't know what's up with the price since they were under $2 for a pack of 5 when I bought some a while back).
They actually come from Parts Express where they're still $1.29 a pack but you'd have to pay extra for fast shipping.

http://www.amazon.com/Littelfuse-500mA-Type-20mm-Slo-Blo/dp/B000XPT21A/ref=sr_1_38?ie=UTF8&s=electronics&qid=1283379471&sr=8-38
 
Probably, but I didn't get a parts list with mine.  I bought the already-built Speedball prototype that was @ CanJam.
 
Grainger49 said:
If the fuse doesn't blow with the tubes out it indicates a problem around or in the tube.  It could be a shorted tube or a problem with the plate or cathode circuit.
Click to expand...

i am having the same issue as the op. checked my wiring 4 times and resoldered all wires to speedball boards twice. blew 4 fuses in the process. just tried turning on the amp without the tubes and left it on for 4 seconds. fuse blew again. will post pictures tomorrow but any specific areas i should look at? i had the amp working just fine without the speedball kit.
 
Blowing fuses without the tubes in can indicate that one or more of the diodes is reversed, one or more of the capacitors is reversed.  It could also indicate a short from a clipped lead landing in the wrong place.  Or none of the above.  But check these things first.  Best yet get someone else who hasn't been staring at it for days to check it for you.  Sometimes you just can't see the problem because you have been looking at it so long.
 
well the amp was running fine earlier without the speedball kit so i dont think the diodes are the issue or the caps for that matter. will ask someone else to take a look at the wiring tomorrow.

here is what the big speed board looks like. i wonder if the 2 deviations i took are causing the fuse to blow. instead of the two wires connecting the B+ and G pads on top of the board, i wired them under the board and instead of using a jumper, i created a solder bridge between the two G pads on top of the board and the same for the B+ pads.

is that where im going wrong?
mop9100517j
 
Since I don't own a Crack (Doc made me say that) much less the Speedball I can only conjecture from general electrical knowledge that you might remove the power from the Speedball and give it a try again.  It should hold.  If there is no power going to the Speedball and it blows the fuse, then there has been a problem created somewhere else.  But it shouldn't blow the fuse. 

If the fuse blows then the problem is very likely on the Speedball board.
 
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