Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: antjuneau on September 13, 2015, 05:26:43 PM
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I've assembled a Crack and all the resistances are accurate but when I plug in the tubes and fire her up most of my voltages are low and I'm not getting any sound in my headphones (not even a buzz). I've checked all the solder connections several times. Anybody know what the issue is? Here's what I'm getting:
1 - (-1.04)
2 - (-1.02)
3 - 0
4 - (-1.02)
5 - (-1.02)
6 - 0
7 - 0
8 - 0
9 - 0
10 - 0
11 - 0
12 - 0
13 - (-1.02)
14 - 0
15 - (-1.02)
16 - 0
17 - 0
18 - 78.2
19 - 75.7
20 - 0
21 - 235
22 - 0
A1 - (-0.9)
A2 - 0
A3 - (0.41)
A4 - 0
A5 - 0
A6 - (-1.04)
A7 - 0
A8 - (0.56)
A9 -0
B1 - (-1.04)
B2 - (-1.02)
B3 - 0
B4 - (-1.02)
B5 - (-1.02)
B6 - 0
B7 - 0
B8 - 0
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First things first, if your voltage checks are way off DO NOT PLUG IN YOUR HEADPHONES!!!
OK, now that we've gotten that out of the way, are the tubes glowing? (Is the fuse installed?)
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First things first, if your voltage checks are way off DO NOT PLUG IN YOUR HEADPHONES!!!
OK, now that we've gotten that out of the way, are the tubes glowing? (Is the fuse installed?)
Yes, fuse installed and tubes are glowing.
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The resistor between 15 and 21 is where the DC voltage interruption is. Carefully wiggle it with the amp off, I'd imagine it's not well soldered.
Be careful, it will take some time for the voltage at 21 to bleed off.
If that resistor isn't loose, it should be getting hot enough to start smoking, which I'm guessing it's not.
It's also possible that one of the black wires may be loose in the power supply, I'd suggest inspecting everything carefully.
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The resistor between 15 and 21 is where the DC voltage interruption is. Carefully wiggle it with the amp off, I'd imagine it's not well soldered.
Be careful, it will take some time for the voltage at 21 to bleed off.
If that resistor isn't loose, it should be getting hot enough to start smoking, which I'm guessing it's not.
It's also possible that one of the black wires may be loose in the power supply, I'd suggest inspecting everything carefully.
Great! Thanks! I'm not at home to try this fix right now but I will give it a shot tomorrow and report back.
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The resistor between 15 and 21 is where the DC voltage interruption is. Carefully wiggle it with the amp off, I'd imagine it's not well soldered.
Be careful, it will take some time for the voltage at 21 to bleed off.
If that resistor isn't loose, it should be getting hot enough to start smoking, which I'm guessing it's not.
It's also possible that one of the black wires may be loose in the power supply, I'd suggest inspecting everything carefully.
The resistor is connected and cool, and all the black wires in the power supply are connected well.
I did notice just now that I'm picking up infinite resistance across the black/grey resistor connecting terminals 19 & 21. Do I need a new one?
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The resistor is connected and cool, and all the black wires in the power supply are connected well.
I did notice just now that I'm picking up infinite resistance across the black/grey resistor connecting terminals 19 & 21. Do I need a new one?
Nevermind, thats a diode not a resisitor. I have checked every single connection multiple times and am still at a loss! Any other ideas?
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Any other ideas?
Post photos and maybe we can see something that isn't otherwise apparent. You are getting the high voltage that you should be, just not past the first 270 Ohm resistor. With the amp off, you can measure that resistor with your DVM just to check to be sure that it's still 270 Ohms (or thereabouts).
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Post photos and maybe we can see something that isn't otherwise apparent. You are getting the high voltage that you should be, just not past the first 270 Ohm resistor. With the amp off, you can measure that resistor with your DVM just to check to be sure that it's still 270 Ohms (or thereabouts).
My meter is showing that the resistance on the 270 ohm resistor is actually a few hundred thousand. It fluctuates so I can't give an exact value, but it's definitely way higher than 270 ohms. The other 270 ohm resistor between terminals 13 and 15 is reading 268 ohms.
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I'd give a replacement a shot. To check the rest of the circuit, you can solder a piece of wire across that resistor, but the amp will be noisy and can't be used until that resistor is replaced (replacement parts can send another one in the mail).
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Just got the replacement resistor in the mail. I checked the resistance across, and it checked out - 270 ohms. So I un-solder the old one and solder in the new one and check the resistance again - 270 ohms. Then I plug in tubes and fire her up... smoke! So I turn it off and check all parts around the power supply to make sure it's all still wired properly. It checks out. I turn it back on and don't see smoke so I decide to check voltages... same as before. Low voltage everywhere. Then I check the resistor I replaced and notice the leads look oxidized. I check it with the meter and the resistance is through the roof - over 2 million.
Apparently both resistors have been burnt up when I turn the amp on. I am extremely frustrated. What's causing me to burn up the 15/21 resistor? Any ideas? I can post pictures if nobody has any ideas off the top of their head.
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Recheck your resistaces, you have a short somewhere in the amplifier.
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A picture or three might help
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See photos
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More
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A couple of things:
1. You used the self-tapping #8 screw for the ground connection instead of the other #8 screw provided. If it hasn't gobbled up the threads on that nut, it shouldn't be the end of the world, but it must have been tough to get the nut to go on well.
2. You are missing a nut on one of your power transformer screws. If you're out of screw thread, double check that the insulating washers are all oriented properly (this is a common mistake).
3. You have a 220uF 250V capacitor in backwards. This is creating a short, which is burning up the 270 Ohm resistor that looks cooked. You can try flipping the cap around to be oriented properly, but you may need to replace it.
Hope this helps.
-PB
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Looking at the 4th photo you posted, it looks like both the nylon shoulder washers (white) and the fiber shoulder washers (black) are on the bottom of your plate, i.e. between the top plate and terminal strip. If you look at page 14 of the manual, you should place the white washers between the transformer and the top plate, and the black washers between the top plate and the terminal strip.
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Thanks guys ---^.
Not sure how I messed these things up, I normally pay pretty close attention to detail. As for the washers, I don't want to mess with those unless you think they'll cause grounding issues... what do you think?
As for the capacitor, I will go ahead and order a new one since I need a new 5W resistor anyway. I'll make sure to orient it properly this time.
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You are not grounding the strips with the washers in the way
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As for the washers, I don't want to mess with those unless you think they'll cause grounding issues... what do you think?
This is very important. Take the time to fix it.
-PB
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Thanks for all the help guys! I made the adjustments you all recommended and now she works.
However I just upgraded the amp with the Speedball and I'm having another issue. All of the LEDs are lighting up except for the one that connects A8 to the centerpin. I'm getting audio through the left channel but silence in the right. Also, the voltage across the A3-to-centerpin LED is 1.5 V whereas the voltage across the A8-to-centerpin LED is 12 V. Any ideas on what the problem could be?