Moving the 12AU7 Tube causes loud clipping/static in left channel

zbells · 1469

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Offline zbells

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I'm running stock and have to tilt the 12AU7 tube back to get sound out of the left and right channel.  I think the pin in A8 won't make solid contact unless I prop the tube back a bit.  This works fine, however when I fiddle the 12AU7 tube or move it around and place it flat, I get really loud clipping/noise (sorry I don't really know how to define correctly) in the left channel, then no sound out of the left channel after a few seconds usually.  When I turn the board over I also see that the LED closest to the front is not lit.  When building the crack, I had to mess around with A8 in order to get the front LED to work and to get the voltages right, so I think it's definitely A8 that's giving me issues.  I've tried to bend and manipulate the A8 socket to fix it, but I'm still having this problem.  Anyone have advice for how to go about fixing A8?  Is my work around OK for the 12AU7 not to make solid flat contact with the socket (a millimeter or 2 gap on the front side to that A8 pin makes better contact on the back side)?  Also, how difficult would it be to replace the 9-pin socket (maybe upgrade idk)?  Thank you!



Offline Paul Birkeland

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Reply #1 on: February 28, 2018, 07:36:32 AM
This is very, very typical of a flaky solder joint.  How is the joint where the LED connects to the center lug of the 9 pin socket?

I think I can remember one case of a 9 pin socket being flaky from the start maybe 10 years ago, but otherwise it's just a loose connection that needs to be cleaned up (or an LED that's damaged from too much soldering).

You are also welcome to wire in a jumper from A3 to A8 which would be a fix for a single damaged LED.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline zbells

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Reply #2 on: February 28, 2018, 03:54:55 PM
Thanks PB.  The joints look good.  I've tried resoldering all 3 the other day.  If anything I have maybe too much solder in the middle pin (might have busted the LED).  I had an issue during the build with bad joint causing popping when i tapped the crack, so i went through and resoldered the hell out of the joints.  Then that problem was fixed, but I have my current issue haha.  I'll try resoldering the middle pin and both LED joints once more.  If that doesn't work, how would I go about wiring in a jumper from A3 to A8 to see if that does the trick?



Offline Paul Birkeland

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how would I go about wiring in a jumper from A3 to A8 to see if that does the trick?
You connect A3 to A8 with a piece of wire...

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline zbells

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Well I'll be... thnx I'll give it a try.