Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: harrislp on March 01, 2013, 04:14:16 PM
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Hello,
I recently built my crack amp and I am having a problem with the last check (the headphone TRS voltage check). I can't seem to get the voltage to stay below 9V or go back to 0V. Whenever I test it on either the tip or ring the voltage jumps around wildly and won't go back to 0V, or at least won't stay there. I have re-flowed all the solder joints and tested all the other voltages (they all check out within the 10-15% range) and resistances too. SO I am a bit stumped and would appreciate some advice and/or help. Thanks in advance :)
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It could just be poor test lead contact with the test point. Try using clip leads to attach the test lead to the test point. The alligator clips will make a lot better contact than the test lead tip. You can buy a bag of them for a few bucks at Radio Shack. I consider them one of the most important tools we use.
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Okay I will give it a go. Thanks. Any other ideas in case it is not the test lead? All the other voltages seem to check out.
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There is a 2.49K (if i remember correctly) resistor across each output that serves to bleed of any potential that builds across the output at statrtup. Make sure it is properly connected.
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I tried to do some troubleshooting and went back and did the resistance checks with the alligator clips. Now numbers 6 and 10 are showing zero ohms resistance when they should be 2.4K, and I have no idea what I have done wrong. All the other resistances are fine, even b3 and b6. I'm getting frustrated now, as the resistances on 6 and 10 were correct when I first measured them. I did the mod and soldered the two unused headphone jack pins to the ground and carefully soldered the 2.49K resistors to the output terminals, and did another full check of my solder joints. So I am, yet again, stumped. I don't want to move on to voltage checks until this is sorted out.
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I did the mod and soldered the two unused headphone jack pins to the ground and carefully soldered the 2.49K resistors to the output terminals,
Yes, you did the mod that shorts 6 and 10 to ground, so they will measure 0 Ohms.
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Okay everything seems to be working, all the tests checked out and I am listening to music on it now. Thanks for your help Doc and PB. Now to build the case. :P
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Okay, new problem :)
I am not getting any sound at all, no buzzing, no crackling, nothing. The RCA 6080 tube is glowing brightly and giving off plenty of heat but the 12Au7A is lukewarm to the touch and the filament is only very faintly glowing in one spot. Is this a faulty tube or some other problem? I've tried several sources with the amp and rechecked my solder joints. I don't have any other tubes to test with and it was working fine a few days ago before I made the case. I seem to remember the 12au7 glowing more brightly and being at least hot to touch, but I could be imagining it. What could be the cause of this? Interestingly, when I have the unit plugged in but not switched on, I am getting a buzz when I pull the headphones halfway out of the jack. Could this be a ground issue?
Thanks in advance.
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It's possible that a bad or missed solder joint worked loose in moving the chassis around. Recheck all voltages and let us know any that are out of spec.
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Okay I checked the resitances and voltages and most of them are out of spec now. I found the red wire at 13U was loose and resoldered it but no change, which was weird as you'd think resoldering a loose wire would at least change something. Maybe I didn't resolder it correctly. Not sure, it's in there tight now though.
The problems I measured are:
RESISTANCE: Terminal 6 reads 0 ohms (should read 2.4K). Terminal 10 reads 0 ohms (should read 2.4K)
Terminals 1,2,4 and 5 all read OL (outside limits) where they should have a readable value (they did before when it was working).
Terminal 13 also reads OL even after I resoldered the wire from B5.
The Right (Red) RCA Jack centre pin reads OL. The left (white) RCA jack centre pin reads 97K ohms, within the expected range.
VOLTAGE: There is no voltage going to the B socket (i.e. B1, B2 etc.) and no voltage on Terminals 1-10 either. I didn't really go into it too much as I got a bit paranoid about it after that and switched it off. I didn't retest voltages after I soldered the wire as the resistances weren't checking out.
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Considering the number of OL readings it might be that some wire that is a ground connection has come loose. Take a close look at all of the black wire connections.
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Okay I've resoldered quite a few joints and now I'm getting the correct resistances on all terminals except for 6 and 10, which are still reading 0 insteadof 2.4K. Also I'm getting voltages to alterminals that should be getting them but some voltages are well over the spec. And the LED from A8 works intermittently when powered up, when i started testing voltages it did not work but then came on when i tested the octal socket and then went off again. What is my next stage of troubleshooting?
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Unless you undid the mod, as CB pointed out above, 6 and 10 should read 0 ohms now. So that isn't your problem.
Check the wiring into and out of the LED at A8. If it is intermittently getting voltage there is something wrong and should be a good starting point.
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I'd post the new voltages.
6 and 10 will still be 0 Ohms.
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NEW VOLTAGES (out of spec in RED)
Terminal 1: 150
2: 169
3: 0
4: 169
5: 84
6: 0
7: 152
8: 0
9: 107
10: 0
11: 0
12: 0
13: 169
14: 0
15: 193
20: 0
21: 219
A1: 84 A2: 0 A3: 1.54 A4: 0 A5: 0 A6: 154 A7: 0 A8: 0 (LED not on) A9: 0
B1: 154 B2: 169 B3: 154 B4: 84 B5: 169 B6: 108 B7: 0 B8: 0
I resoldered the LED on A8 but no dice. The led does work but not during normal operation.
Thanks,
Harris. :)
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I would start by rechecking the diode. I would probably just replace it. Then check that nothing is touching something it shouldn't be around T1, 2 and 7. And then that the connection at B3 is good.
I'm sure CB will have a more technical solution. He always seems to get me up and running.
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I'd touch up the solder joints on the LED that doesn't work.
Also touch up the joints on the 22K resistor between terminals 1 and 2.
All the high voltages are related to this, once that LED is glowing, things will drop into line.
-PB
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Looks to me like one side of the 12AU7 is not glowing. Could be a bad tube, but more likely a bad connection at A5. Check connections at A4 and A5 (and examine the tube closely while it is on).
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Thanks guys for all your helpful replies, they are much appreciated. I tried all the suggestions (apart from a new diode as I don't have one) and nothing worked. My readings are still the same after touching up all the joints on the A and B sockets and the terminals 1,2,7. I even did a few others that looked suspicious. The LED will not come on at all now, so I suspect I will need to ask for a replacement, correct? Then try a new tube? I've resoldered till I'm blue in the face :o
Where would I obtain a new LED from?
Any and all suggestions are welcome -- I will get this thing working before my birthday (April 26). I hope.
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You can give us a call and request some replacements, I'm guessing the voltage at T5 is now higher than it should be?
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I'm guessing the voltage at T5 is now higher than it should be?
No, it is still reading 84V, same as it was before. terminal 1 is still 154V though.
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I switched the diodes around and the same diode that wasn't working before is now not working in the other position, so I guess I have a dead diode. I have emailed Eileen asking for a couple of new ones, is this the correct protocol?
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Hello, I'm back again! 8)
Got the replacement LEDs (thanks Eileen for your excellent service) and soldered them in, they both lit up. Excellent. I measured all the voltages and they checked out, did the voltage check on the headphone jack and it was fine. Then I went back and checked the resistances and they all checked out, except the ones with the star in the manual (1,2,4,5 and 13) all showed O.L (outside limits). All the other resistances checked out.
Should I be worried about this, or is it okay? I need to be sure before I plug any headphones in, i'm paranoid after I burnt out a driver in my Beyers after not properly checking the output voltage of the headphone jacks after the initial build. :'(
Thanks,
harris.
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If the voltages on the tubes check out you should be fine.
Enjoy some tunes.
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I plugged in some headphones and it worked great for a bit but then it felt weird, like the headphones were getting voltage or something, the same as it did when I burnt out the driver. I turned it off and tried to turn it back on again but the LED has stopped working, on the A8 pin as it did before. I still have one spare LED but I don't want to put it in just so the whole thing happens again. Is it plugging in the headphones that is causing the LED to short out? It was working okay before I plugged in the headphones. The voltages are back to how they were before I replaced the faulty LED (see earlier post), so there's definitely something wrong. It's lucky I live on the ground floor or else this thing would be in many many pieces. What am I doing wrong that this thing will not work! Very frustrated. What should I try next?
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So terminal 1 now has high voltage again? Do both sides of the 12AU7 glow? If one of the LED's isn't lighting, then either that side of the tube isn't getting heat, the LED isn't properly soldered, or the 22K resistor between T1 and T2 isn't properly soldered.
Plugging in the headphones will have no influence on the LED's, the headphone output it on the opposite side of the circuit, isolated by the 6080 and coupling caps.
I wouldn't just replace the LED again, there is some evidence that this wasn't the problem to begin with. Check the connections and components that go to A4/5, A6, A7, and A9.
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I took a picture of the unit when it is on. I don't think the 12AU7 is working properly, there were two filaments that lit up before the LED blew out but now that doesn't seem to be the case. I'll try reflowing and resoldering again after work and see how that goes, but this one is the most puzzling to me of the myriad problems I've had with this thing. It seems to work for a bit and then get overloaded or something. Thanks for your help, hopefully it's just another soldering issue.
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Try pulling the 12AU7 tube and measuring resistance across pin 4 and pin 9, and then across pin 5 and pin 9. Those are the two halves of the heater. Each should read low ohms.
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I got around 6.5 ohms each for these two measurements, Doc. I assume that's normal?
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Yeah, that means the tube heater is OK. So if one half is not lighting there may be an issue with the tube socket or the wires connected to pins 4,5 and 9. Or the heater might be working OK and just looks odd. The next check should be to see if you measure 6 volts or so from B4 to B9 and from B5 to B9.