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July 08, 2020, 04:20:29 PM

Author Topic: Bad 6080 tube  (Read 328 times)

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Offline freejazz

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Bad 6080 tube
« on: June 18, 2020, 08:53:15 PM »
I believe that after only one week of use my 6080 tube has gone bad. I get the worst popcorn sound out of both channels. I can't use the amp. When I swap the tube with another from a friend the popping goes away. Is this typical of Cracks? Thanks, /d

Offline Paul Birkeland

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Re: Bad 6080 tube
« Reply #1 on: June 19, 2020, 04:58:41 AM »
That would not be normal, but what would be really abnormal with a problematic tube would be to have both channels do something like that, and to start doing it at the same time.  If you tap hard on the amp while it's running with that tube, does that change the nature of what you're hearing? 

Very, very often we see posts like this where a tube swap will change things, but eventually the new tube also exhibits the same symptoms, and it ends up being loose solder joints that are moved around by the tube swapping process.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline freejazz

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Re: Bad 6080 tube
« Reply #2 on: June 19, 2020, 07:48:59 AM »
I will try to tighten the physical connections and reflow all the solder joints at the tube sockets. A quick review doesn't show me any loose joints. You may see something different. I can add more photos if needed. Tapping on the tube produces sound in the headphones but doesn't appear to resolve the popcorn. Same with tapping on the top plate. Interestingly, to me any way, is that the sound start out like ticks on a record and then moves toward all-out popcorn as the amp gets continued use. Thanks, /d

Offline Paul Birkeland

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Re: Bad 6080 tube
« Reply #3 on: June 19, 2020, 08:03:20 AM »
That is what I would expect for an amp with a loose joint.  I would recommend reflowing all of the joints in the amp, and I would expect that to make a big difference.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline freejazz

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Re: Bad 6080 tube
« Reply #4 on: June 19, 2020, 08:20:48 AM »
i just powered up the amp again and... no popcorn. i'll reflow the joints and report back. Thanks,

/d

Offline tim273

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Re: Bad 6080 tube
« Reply #5 on: June 20, 2020, 07:38:59 AM »
I have a couple of socket savers, one for each tube similar to these: https://www.amazon.com/Yibuy-2-7x2-27cm-Bakelite-Socket-Amplifier/dp/B078WJ3H71  That way if you like to tube roll, you're not putting any pressure on the sockets.  Seems to help from what I can tell.

Offline freejazz

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Re: Bad 6080 tube
« Reply #6 on: June 27, 2020, 10:19:43 PM »
After reflowing the solder on the tabs of the tub socket i can't seem to get rid of the noise. What should be my next steps. I should note that noise is predominantly in the left channel, but can occur in both. Thanks,

Offline Paul Birkeland

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Re: Bad 6080 tube
« Reply #7 on: June 28, 2020, 05:04:38 AM »
Take a wood chopstick and a cheap pair of headphones, then poke around the bottom of the amp with the chopstick while wearing the headphones to see if you can poke anything to set off the noise. 
Paul "PB" Birkeland

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Offline freejazz

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Re: Bad 6080 tube
« Reply #8 on: June 28, 2020, 10:06:08 PM »
So only two things make noise when being tapped with the chopstick. The first is the 12au7 tube. That sucker is super microphonic and tapping makes the same sounds i'm hearing when I hear the popping/hissing. Tapping on the leads to the tube socket makes no sound so it appears to be the tube and not the wiring. I'll try to find a 12au7 tube to swap out.

The other thing that makes noise when being tapped is the black lead the goes from the headphone input to the terminal strip adjacent to the 12au7 tube. Since I have the Speedball upgrade installed I'll need to investigate this further when I have time to take the big speedball board off to access the terminal strip. The wire running from the terminal strip to the volume pot doesn't make noise when tapped so I'm guessing that the problem is on the headphone jack end.

Interestingly, the noise gets worse as the amp heats up. Is this more indicative of a bad solder joint? Or a bad tube?

Thanks,

/d

Offline Paul Birkeland

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Re: Bad 6080 tube
« Reply #9 on: June 29, 2020, 06:13:49 AM »
The solder joint where the black wires meet on the headphone jack is one that is tough for people to properly solder.  I often find that one wire will be soldered to the jack and the other wire will be loose and passing through.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline freejazz

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Re: Bad 6080 tube
« Reply #10 on: June 29, 2020, 06:26:09 PM »
That did it. That was a great lesson in how to check for bad solder joints. Many thanks. I am amazed that the noise would show in a way that appeared to be related to a tube.

That said, it is now clear that the volume pot needs to be replaced (the right channel is louder than the left throughout the listenable range). Also, I need a less microphonic 12au7. I have a few of both, although I’ll need to drill out the hole for the pot. I guess now would be the time to plan any other “upgrades.”

The amp sounds great. Thanks again for the help.

/d

Offline Paul Birkeland

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Re: Bad 6080 tube
« Reply #11 on: June 29, 2020, 07:32:28 PM »
Check out the Crack FAQ for a mod regarding channel imbalance in the volume pot.  That can be padded down with a couple of inexpensive resistors.  I do that to every Crack that I factory build.

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline freejazz

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Re: Bad 6080 tube
« Reply #12 on: June 29, 2020, 10:12:25 PM »
I will try that, but I think I'll preform the upgrade anyway. First, the pot is noisy when I turn it, and second, I have spare parts just sitting here. The spare I'm likely to use is an Audio Note, which is the right size and value (100k). I also have a Kozmo that didn't get used in another project, but that is likely a bit too much of an attenuator for this project (that is, cost to application). Goldpoint would be my first choice, but that is yet more expensive. I've got other random parts sitting around from old projects (caps - after the volume pot my most likely upgrade, Cree diodes - this one's a bit in the air, headphone jack - not likely do to this one since the one with the kit seem to be fairly high quality) that I may or may not implement at some point just to try it.

How does the resistor addition you're recommending work? is it pre-attenuation or something else?

Thanks,

Offline Doc B.

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Re: Bad 6080 tube
« Reply #13 on: June 30, 2020, 06:08:27 AM »
Quote
I am amazed that the noise would show in a way that appeared to be related to a tube.

Pretty much anyone but fairly experienced builders tends to assume that any problem with a tube amp is due to a "bad tube". I think it's a natural extension of the fact that tubes are plugged into sockets and therefore are the only thing that can fail and need to be replaced.

The reality is that the parts supplied with the kit are much less likely to be bad than the possibility of some glitch in the assembly of the kit. This is why I have repeated for years that the best thing to do with an intermittent problem is to reflow every solder joint in the kit. Unfortunately some users resist that notion, based solely upon a quick visual inspection that can't really tell you if a joint is conducting properly. I'm glad you took the advice to heart, found the issue and got it sorted.
Dan "Doc B." Schmalle
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Bottlehead Corp.

Offline freejazz

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Re: Bad 6080 tube
« Reply #14 on: June 30, 2020, 08:42:23 AM »
Yes. This has been a great learning experience for me. To date I have only done solid-state DIY projects. Pretty much entirely Pass. I wanted to build this kit for some time, I really enjoyed it, and I learned a lot. On top of that, I think it sounds great. I’m looking forward to my next Bottlehead kit. Also, I wanted to thank you for your patience and suggestions. Maybe with the minor mods I’ll have more questions.

About the resistor trick, is that pre attenuation or something else?

Thanks