Sound faded away from one channel / High voltage readings on Crack [resolved]

[Tom-s]

On the small sockets. Check if pin 4 and 5 are still properly connected.

[kattjaevel]

What is a good way of testing that? Visually they look similar, not one that is pulled out further or anything. When I look at them from the top I can see both sockets look just like the others.

[Paul Birkeland]

OK, this is usually an indication that the solder joint at A4/A5 is not doing its job. 

[kattjaevel]

I redid the soldering on A4/A5, as well as B7/B8 (both from the transformer and from B to A). I can with confidence say that these connections shouldn't be an issue any longer. I made sure that they were solid and didn't move a millimeter before soldering and made sure to solder properly. Redid voltage readings. Still the "left" side of the board measure too high. Here are some outstanding values...

T1: 140V
T2: 160V
T4: 160V
T5: 95V

T7: 140V
T9: 108V

A6: 140V

B1: 140V
B3: 140V

[Paul Birkeland]

Do both halves of the 9 pin tube glow?  If not, and you're confident that your connections are good, I would replace the 12AU7.  If the new 12AU7 has one half that doesn't glow, then you will need to go back over those heater connections.

[kattjaevel]

No, still only the bottom half of the 9-pin tube glows. I'm quite certain that these connections are solid. They didn't budge at all no matter how much I tried moving them before soldering and the physical connection between the pin and wire was solid. I'll try with another 12AU7. Thanks.

In the meanwhile, is there anything else in the chain that could be causing these voltage issues or is it because the 12AU7 doesn't "draw" any current? Could for example my A-socket pins have been pulled out so that they don't connect to the tube any longer? Can I measure something like that? I tried shining a flashlight down the sockets and saw nothing apparent that would be the issue of the sort, but guess I might as well ask an expert. Appreciate all the help

[Paul Birkeland]

If only one half of the 12AU7 is heated, then only half the tube will operate, and you'll get flawed voltage measurements and no sound out of that channel.  That's the impetus for focusing only on that and not looking for problems elsewhere.

[kattjaevel]

Well, the 12AU7 finally arrived in the post. Swedish postal service at it's finest, 3 week delivery... anyways, I installed the new 12AU7 and redid resistance and voltage measurements, everything works now