Two leds not lighting on c4s

Matt Rendall · 22121

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Offline Matt Rendall

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on: January 10, 2020, 03:38:56 PM
Hey, I need some help after my Integration upgrade. I actually potentially have two issues.

1. The two leds on the B side of the right channel c4s board aren't lighting and one of my voltages is off.
Voltages:
56 - 126v
29 - 108v
4 - 105v
26 - 74v
31 - 71v
2 - 90v
15 - 106v

I reflowed all the joints on that side of the c4s board, no change. Then I swapped tubes and the two B side leds on the left channel c4s board don't light, and the 106v has moved to 26. Right side seems fine. Maybe a tube is bad? I unfortunately don't have any spares to test with. Would a tube work before the upgrade but not after? No music comes out of the channel with the bum leds.

2. When I finished the Reduction, it sounded great but I had a bit of very low level static-y noise in the left channel. I attributed it to a bad ground somewhere (My Crack had the same sound which was fixed by fixing the grounds). I left it alone because it was low-level enough and I was planning on doing this upgrade after about a week anyway. As part of the upgrade, I reflowed and checked all my grounds. After the upgrade, the static is much louder, almost at music level. And when I switched tubes as part of troubleshooting the first issue, the static moved to the right channel. Any ideas on troubleshooting this one?

Thanks for the help.


Offline Paul Birkeland

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Reply #1 on: January 10, 2020, 05:10:28 PM
It sounds like it would be prudent to procure an extra tube.

Can you post photos of the build? 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Matt Rendall

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Reply #2 on: January 10, 2020, 06:08:55 PM
Hey, thanks for the response. I'll attach a few. Please let me know if you want to see any specific parts closer.


Offline Paul Birkeland

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Reply #3 on: January 10, 2020, 06:40:40 PM
Something you might find helpful is loosening the top nut on the ground post so those solder lugs are free floating, then reflow the solder joints on them.  They are tough to solder when the nut is torqued down, as the heat will tend to migrate into the chassis rather than sticking around to make the solder flow.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Matt Rendall

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Reply #4 on: January 11, 2020, 04:26:46 AM
Ah yeah that was much easier. I cleaned up that ground but it doesn't seem to have helped either issue. And the behavior switches channels when the tubes are swapped.


Offline Paul Birkeland

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Reply #5 on: January 11, 2020, 06:39:54 AM
I'd grab another Russian 6DJ8 and see if that helps. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Matt Rendall

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Reply #6 on: January 11, 2020, 11:33:22 AM
You mean buy one from eBay or something?


Offline Paul Birkeland

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Reply #7 on: January 11, 2020, 01:06:11 PM

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Matt Rendall

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Reply #8 on: January 11, 2020, 01:44:24 PM
Wow those are super cheap, yeah might as well get two. Will these sound "as good" as the ones originally provided? I don't know much about tube rolling.


Offline Matt Rendall

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Reply #9 on: January 12, 2020, 09:07:52 AM
Well yesterday I found a tube on Amazon with free 1 day shipping. It seems to fix everything. The one original tube I was having problems with just doesn't work at all, the other original works but is noisy, and the new one works perfectly, in either channel. Voltages and everything all look good.


Offline Paul Birkeland

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Reply #10 on: January 12, 2020, 09:20:48 AM
We have found that a lot of these old stock tubes that haven't been used in decades will quiet down if you let them run for 100 hours. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Matt Rendall

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Reply #11 on: February 07, 2020, 07:21:13 AM
Just wanted to follow up and say that the suggested cheap Russian eBay tubes solved the issues I was having. Both channels are dead silent and make identical gain as far as my ears can tell.

I did some reading for a few weeks and have a $40 pair of NOS Amperex 6DJ8s on the way, which I think will sound a bit nicer.


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