Voltage check failure following Crack build [solved]

[casctu]

Hi guys,

I just finished the construction of my Bottlehead Crack, and the resistance check was fine, but the voltages are off.

In case it is useful, here are my resistance readings:

Terminal           Measured Resistance
1                      Not 0
2                      Not 0
3                      0
4                      Not 0
5                      Not 0
6                      2.48
7                      2.951
8                      0
9                      2.949
10                    2.482
12                    0
13                    Did not climb towards 270, but started at around 500 if I recall correctly, and continued dropping
14                    0
20                    0
22                    0

B3                    2.951
B6                    2.95

The RCA Ground Lug read 0, the Right Center pin read 102.4, and the left read 103.7.

Here are my voltage readings:

Terminal          Measured Voltage
1                     78.4
2                     159.99
3                     0
4                     159.99
5                     143.5
6                     -5 to 20 (jumps around, doesn't settle on one number)
7                     99.3
8                     0
9                     142.8
10                   0 to 30 (jumps around, doesn't settle on one number)
11                   0
12                   0.3
13                   159
14                   -0.5
15                   186.6
20                   -0.7
21                   214.7

A1                   159.2
A2                   0.6
A4                   -0.3
A5                   -0.3
A6                   77.1
A7                   0.3
A9                   -0.4

B1                   77.1
B2                   158.8
B3                   98.9
B4                   142.7
B5                   158.7
B6                   142.1
B7                   -0.3
B8                   -0.3

The unit powers on and both tubes light up. Before I powered it on for the first time, I double checked all the connections and soldering joints, and couldn't see anything that appeared out of place. Could anyone point me in the right direction?

Thanks in advance

[Paul Birkeland]

Are both halves of the 12AU7 glowing?  (I'm 99% sure that one of your LED's isn't lit also, just be sure it's in with the striped end toward the center lug of the 9 pin socket)

If 6 and 10 appear to be jumping around, your meter may be jumping around on the mV scale, it'd be worth double checking.

[casctu]

The bottom part of the 12AU7 is lit up, but the top part is only faintly lit near the front and the back doesn't appear to light up at all (or barely at all). Both of the LEDs light up when the unit is powered on, and I made certain when I soldered them that the stripe was towards the center. I did have to resolder a wire that connected to the center lug of the 9 pin socket during the build, so it is possible something changed, but I was able to resolder the wire without having to remove the LEDs, so they should still be soldered correctly.

Not sure if I should have or not, but I connected a backup pair of headphones and I'm not getting any audio from the left channel.

I have an autoranging multimeter (it's an Agilent U1232A), but I will try setting its range manually to see if there is any difference in the reading and will let you know if it reads correctly.

[Paul Birkeland]

A 12AU7 has a pair of vertical plate structures inside the tube.  You should be able to see a little bit of orange glowing from the top, bottom, or top and bottom of each of those plate structures.

If you only see glow on one side of the tube, that would narrow down what you're experiencing. 

[casctu]

I've attached a picture - only the section circled in red is lighting up - do I need a new tube?

[Paul Birkeland]

OK, both halves are lighting.

Can you post a photo of the 9 pin tube socket wiring?

[casctu]

Sure, no problem. Not sure why in hindsight, but I soldered the LEDs so they would be facing up. If necessary, I can resolder them and flip them over so it is clear which way the stripe is facing. If there's a specific area you need a better view of, let me know.

[Paul Birkeland]

The wire leaving A1 goes to terminal 5, not terminal 4. 

You should have sweet tunes after you move that wire.

-PB

[casctu]

Awesome, thanks for the help - sounds great

Can't wait to get the speedball upgrade installed