Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: Justin on April 06, 2019, 04:55:32 AM
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Hi, forum. I'm currently putting a Speedball together and ran across a snag I'm hoping to get some help with. I previously built an tested the Crack which worked well, was in spec and sounded impressive. I installed the small board for the Speedball and after some troubleshooting I realized I installed the MJE350s the wrong way. Before fixing this I was getting readings of:
OA - 0
1A - 202
B-A/B - 0
1B - 203
OB - 0
After correcting the orientation of the MJEs I remeasured and am currently at:
OA - 144
1A - 162
B-A/B - 0
1B - 162
OB - 137
All LEDs light up. When I follow the diagnostic flow chart I'm hitting a dead end where it tells me to check voltages at A2 and A7 - both values in my kit are below 1 volt. I've re-soldered anything on the board that looked remotely sketchy. Anything obvious I'm missing that would explain the high OA/OB numbers?
Justin
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Would it be possible for you to post some photos of your board? If you can unscrew the screws that hold it down, you should be able to take a photo of the top and bottom without pulling it out of the circuit.
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Sure, see attached.
FYI the middle lead of one of the MJEs broke when I was removing them to fix the orientation but I feel like I was still able to get a decent connection when I re-soldered it to the board. I don't think that's causing my problem but who knows.
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I think I see some of the board trace that has come off in this photo. This can happen without the proper tools if you try to pull the transistors. To be honest, I would contact replacement parts about just getting a new small board plus parts, as this one is likely beyond being salvaged.
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10-4, hadn't noticed that. Thanks for the quick replies.
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Hi Paul. So I ordered a replacement board (got it lightning quick btw, like 3 days quick!) and after I reassembled and installed both boards I'm getting similar readings on the little board along with high readings at OA and OB on the bigger board.
Little Board:
OA - 155
1A - 184
B-A/B - 0
1B - 184
OB - 140
Big Board:
OA - 150
OB - 160
G - 0
B+ - 184
All LEDs light up although the ones on the little board are dim. The amp works and sounds incredible. These numbers are clearly out of range - any ideas what might be causing them? Just let me know if you need any more photos.
-Justin
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Please don't listen to an amp that doesn't pass its voltage checks, it can damage your headphones and potentially cause bodily harm.
Can you pull the 6080 tube and measure just the small board with the 12AU7 installed?
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Okay, thanks for the advicel.
The values on the small board with the 6080 pulled are:
OA – 150
1A – 228
B-A/B – 0
1B – 229
OB - 135
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Do the LEDs on the 9 pin socket light up when you perform this test?
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Yes, all LEDs light up on the 9 pin socket and the small board with the 6080 removed.
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Can you very carefully get DC voltage measurements for A2, A3, A7, and A8?
-PB
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Sure.
A2 - 0
A3 - 1.58
A7 - 0
A8 - 1.57
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And you have a 12AU7 plugged into the 9 pin socket, not some other type of tube?
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Yeah, its the one that came with it. I just substituted a different 12au7 from another amp and got 111V OA and 115V OB on the big board. You think that was it?
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No, there's a bigger underlying issue here.
Can you post some new photos of the top and bottom of the current small PC board?
Do you still have the 22K resistors that you removed when installing the small PC board?
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I appreciate the help.
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I would go back to the 22K resistors instead of the small PC board, then continue debugging the circuit. The issue you're experiencing is likely something iffy with the underlying build.
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Alright. I'll have to order some new ones and get back with you later on. Thanks
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Oooookay. New 22.1K resistors in place of the small board. I retraced every step in the instructions from point to point (I'd be surprised if it were miswired at this point but foolish to rule it out), and carefully inspected and re-soldered any joint that I didn't like. During this process I found a couple of wires i'd attached to a lower terminal that i went ahead and corrected to the upper as the instructions called for or visa versa, but nothing that I think would affect the current. Right now my resistance and voltage terminal checks are as follows:
Resistance Voltage
1. * 131.5V
2. * 186
3. 0 0
4. * 184.5
5. * 124.7
6. 0 0
7. Over Limit 144
8. 0 0
9. Over Limit 140
10. 0 0
12. 0
13. *
14. 0
20. 0
22. 0
B3. Over Limit
B6. Over Limit
RCAs in spec
I can provide any other measurements or pictures as necessary. Any ideas?
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I am going to guess that your LEDs on the 9 pin socket aren't lighting. When you look at the 12AU7 with the amp on, do both halves of the tube glow?
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No, both LEDs on the 9 pin light up fine and both halves of the tube glow.
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Can you post some new photos? I suspect that one of the black wires that makes up the ground buss isn't well connected.
Can you also measure the voltage at A2 and A3 again carefully?
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A2 is 0, A3 is still 1.58V.
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Figured it better to give you too many than not enough
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What is that gray metallic wire crossing the amp that ends near the green heater wiring on the transformer? Is that your solder? If so, and based solely on its diameter, it looks a lot like plumbing solder not electronics solder.
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Plumbing solder would cause strange things like this to happen. I'd also love to see a photo or two of your 12AU7, which sounds strange, but it's good to be sure.
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No, the soldier is 60/40 rosin core for electronics. I'm not sure what you're needing to see with the 12UA7 pics but heres a few - let me know if you wanted to see a different angle. It came in an old RCA box with the amp, and I've tried a few others which will alter the high voltages slightly but not to within spec.
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Well, that's not a 12AU7...
If it came from us, it might've snuck into a 12AU7 box on accident.
(I feel less crazy now BTW)
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Oh wow, okay. Then the others I swapped in were all 12AT7 equivalents as well maybe. The 5963, ECC83, and CV4024 I tried would just give me similar values to the 12AT7 I started with, right? I guess I don't have a true 12AU7 here to check if that fixes it. I'll let the forum know if that solves my issue when I get the right tube, but I gotta say it feels good to know you think that's it, Paul. I've got 98 extra 22.1k resistors with your name on them if you want them! ;D
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The 5963
This is a 12AU7
, ECC83,
This is not a 12AU7
and CV4024
This is not a 12AU7
You need to run the amp with the 5963/12AU7. The other tubes will destroy the amp. The other tubes you are trying are absolutely not compatible with the Crack.
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Success! It's running fine with the 5963 in it. Thanks for sharing your expertise with the community, Paul. It really is an invaluable resource. For anyone reading who might have been on the fence for some reason, these amps are amazing and the Bottlehead team really does run their business with customers in mind. Truly grateful.
Justin
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I'm glad you had a spare around to get it sorted!
-PB