Occasional popping sound - pictures and initial troubleshooting [resolved]

Good to know. There is a tiny bit of solder on the white plastic socket between pins A4/A5. I’m wondering if that could be the cause of my problem? I tried to snag a photo of it but it’s nearly impossible to get an accurate looking shot of it. Is there a good way to try to clean that out without reheating the solder and trying to use a solder pump? As you’re aware, I don’t have a ton of real estate to work around in, so I don’t know how possible that attempt would be…

I may just try to suck as much solder out from A4/A5 pins and start that connection over again…
 
Should I have the actual pins be soldered together? I had it configured this way before I started this troubleshooting process, but removed that solder a few days back. It looked like the pins were separate in the instructions, but since I originally had them soldered together, it makes me think I read that somewhere in the instructions while I was initially working on my build… either that or I just made a mistake, which is most likely!  :)
 
It's also possible that you have some dirty tube pins that are giving intermittent contact, and these can be cleaned by simply pressing the tube into a piece of steel wool a few times.  There's a very remote chance that the 12AU7 has an intermittent internal connection, but this is extremely rare and typically comes up when we test the tubes prior to shipping.
 
This was something else I was considering, so I’m glad you mentioned it. The tube that gave me issues this morning is one I bought secondhand online for tube rolling, NOT the one y’all had sent me in my kit. I will try my amp again with the tube Bottlehead included. I’ll also clean the pins on both tubes, just to be safe.
 
I don't want to jinx it, but I think I may have found and fixed my issue. I was using a power cable from another amp that I was using while I worked on my Crack. That power cord sort of fit my Crack, so I didn't think anything of it at the time. But it was pretty loose. I ended up using the proper power cable that came with my Crack kit and it fit MUCH snugger. Since making that switch, I haven't had any issues and I'm now a couple hours into music playback. I also cleaned my tube pins for good measure, and am using the tubes that came with my Crack for now. So far so good! Fingers crossed! I'll probably send another follow-up in here later tonight after logging a few more listening hours while I work, but I am thinking this may be resolved!!  ;D
 
After ~5 hours or so of listening, I have had 0 issues with buzzing/popping. I think it’s probably safe (knock on wood) to mark this one as resolved. Thank you again so much for all of your guidance, Paul!
 
Argh, this is the never-ending problem apparently! After hours of consistently excellent playback, this morning after another “pop” I lost all audio from the left channel. The small 12AU7 tube stayed illuminated completely, leading me to believe this is an LED problem. Based on an earlier comment from you, Paul, and some searching around, I suspect I’ll need to remove that A3 LED and jumper A3 and A8 with a wire. Super newbie question incoming, but does it matter which color wire that came with the kit I use, or are they all created equal? Thanks!
 
White, black, or red would be a good idea.  There are voltage issues that would come with a dead LED that would confirm this is the issue.
 
Thanks for the quick response. What would be some troubling voltages to keep an eye out for - or are there too many possibilities to list them all? I tried powering on/off the amp a few times and was still not getting any audio out of the left channel, so I’m hoping the problem is constant enough to be replicated when I put my amp back on my work bench later tonight…
 
Based on your reply on page 2, I think my LED on A3 is no good. I think my voltages are in range off the top of my head, except for terminal 5 and A3 (which is right around 12 V):

1. 81.6 V
2. 166.6 V
3. 0 V
4. 166.1 V
5. 149.1 V
A3. 12.7 V

Also, I noted the following during testing. Prodding terminal 5 for the voltage check resulted in crackling in both channels (likely due to the high voltage? But maybe a sign of a bad solder joint). The A3 LED was dark. Still no sound in left channel, like earlier.
 
10-4. Any recommendations re: length of wire, amount stripped back at each end, clip off the dead LED I assume, etc.?
 
So the saga continues…  :) I jumpered A3 and A8 and am now registering expected voltages at both socket pins. All of my other voltages measured at terminals 1-10 also appear to be in range:

1. 84.1V
2. 172.6V
3. 0V
4. 172.6V
5. 81.9V
6. 0V
7. 104.7V
8. 0V
9. 105.5V
10. 0V

A3. 1.59V
A8. 1.59V

However, I am still having some occasional loss of sound in my left channel. This isn’t a consistent loss of sound like I was experiencing prior to this jumpering. The only thing I can think of is that the LED lead connected to A8 doesn’t go through the pin. Rather, it was sitting on top of the pin and then I soldered it on. I was having an extremely difficult time getting both the LED lead and the jumper wire through that small hole. If that was the cause of my issue, I’d expect the right channel to be impacted, but my issue still seems to just be exclusive to that left channel… but I may be wrong about that…

Edit: To add to that comment, I’ve never seen the A8 LED go dark during voltage measurement when I have the undercarriage of the chassis exposed. Not that this would necessarily mean anything, but if it was responsible for loss of sound/power, I’d expect to see it flickering some. Again, not sure how accurate my line of thinking is though.
 
Unfortunately we find that our customers really like to zero in on the LEDs when there's something amiss with a Crack kit, and often they will poke, prod, and resolder them until they break without achieving any meaningful results. 

A drop in sound should come with a change in voltage, and knowing what that is can more precisely direct your efforts.

Keep in mind that when you had a dark LED, we had to measure voltages to even understand what that meant.
 
I’ll try to measure different connections and look for drops during sound loss. Any terminals or pin connections that could be good candidates to start with, ya think?
 
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