Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: timbro52 on July 31, 2010, 12:26:51 PM
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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
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If it's one of the first run of the kit there may be errors in the manual:
http://www.bottlehead.com/smf/index.php/topic,657.0.html (http://www.bottlehead.com/smf/index.php/topic,657.0.html)
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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.
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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
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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.
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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
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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.
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Hello Tim, did you double check the orientation of the power supply capacitors? How are the resistance checks?
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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...
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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.
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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".
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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
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local Radio Shack had what I needed, I just didn't look hard enough.
thank you!
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I bet that the parts list has a good description of the ratings and type fuse that is included.
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Probably, but I didn't get a parts list with mine. I bought the already-built Speedball prototype that was @ CanJam.
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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.
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.
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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.
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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? (https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fyfrog.com%2Fmop9100517j&hash=50545f93bc01c26d5d08a342ca012d306c17171e)
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for some reason i cant post the picture in the above picture...
here is a direct link.
http://img816.imageshack.us/img816/7381/p9100517.jpg
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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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What are the values of the resistors in the R1 position on the large board? I cant tell by the pict. but on mine the R1 positions on the large board has a smaller resistor (1/8? watt 31.6 x2). Parts may have changed, but that's what stood out for me.
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the resistors are 33ohms. the kit does come with 31.6ohm but long story short, i screwed something up and had to use the 33ohms. the 31.6 ohm resistors are otw. the only other thing i can think of i might have done incorrectly are the MJE350s on the smaller boards. i didnt get either with the metal backs (mine have all plastic enclosure) so i checked online to find out which the "back" side was. the way they are soldered in right now - the face that reads mje350 (and has 3 circles) faces away from the leds on both boards. did i get that backwards?
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Here is the proper orientation for the MJE 350's without a metal plate.
The great parts famine of 2010 has forced us to look for substitute parts for many of the kits we manufacture. These substitute parts are of equal or better quality, but some look rather different than the original parts we used in producing the assembly manual. The latest case is one that will cause some confusion -
For the past 14 or 15 years we have used MJE 350 transistors that have a "front" black plastic side with the MJE 350 designation printed on it. The other, "back" side of the transistor is metal.
The current batch of Fairchild transistors we purchased do not have a metal side. One side is printed with the MJE 350 designation, and this corresponds to the "front" side of older transistors. It can also be identified by the three small dots imprinted in the plastic around the center hole. The "back" side, that corresponds to the metal side on the old transistors, has a more matte finish with no printing except for one small dot impression.
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33 ohm should be close enough (4%) Everything looks good from the top side. I guess the best thing is to be sure that the wiring is correct. Are you using .5A fuses or 1A fuses? I had this problem with a early edition of the crack (see my previous thread http://www.bottlehead.com/smf/index.php/topic,677.0.html ) maybe that's it?
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hmm, i grabbed a handful of 1/2A fast blowing fuses from radio shack. should i get 1/2A slow blow or 1A slow blow now? wonder if that is all that is the issue...
also, the orientation of mje350s is correct in my build in accordance with the post. rechecked all the wires and solder joints again. everything is going where it is supposed to go.
thanks again for all the help guys.
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I would go 1A fast since .5 seems to be the intended fuse, and it dose not seem to be quite enough (forgive me if I'm wrong). The 1A gives more room, but the fast blow will die faster than slow, if something is REALLY wrong, which has to be a good thing.
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should be 1A slo blo
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running the amp with .5A slow blow. everything works and sounds great. dismantled and reassembled the whole thing 4 times for nothing >< hehe. the speedball kit really does help. moar impressions later :p need to spend the rest of the day listening to some toones. man this amp sounds great.