Voltage Issues (2-3x values?) [resolved]

[Sixth.Gear]

Hello all! I've been patiently assembling my Crack over the past few nights and finally reached the resistance and voltage check and am getting some extremely odd voltage values.

Resistance check was passed successfully, with a minor difference of:

Terminal 7 2.9K (2.8K measured)
Terminal B3 2.9K (2.8K measured)
Terminal B6 2.9K (2.8K measured)

Voltage check yielded:
1 218
2 218
3 0
4 218
5 83
6 0
7 0
8 0
9 0
10 0
11 0
12 0
13 218
14 0
15 228
20 0
21 239

A1 82
A2 0
A4 0
A5 0
A6 218
A7 0
A9 0

B1 218
B2 218
B3 0
B4 82
B5 217
B6 0
B7 0
B8 0

Something is obviously wrong, but I have no idea where to start. The 12AU7 edit: 6080 (large) tube is also not glowing at all. The 12AU& has both LEDs lit and tube is lit. Here's a link to pictures of connections to help troubleshoot as I'm at a complete loss:

 

[mcandmar]

Your socket for the 6080 tube is in the wrong position, they key for the tube should be pointing towards the smaller tube.

 

[Sixth.Gear]

Your socket for the 6080 tube is in the wrong position, they key for the tube should be pointing towards the smaller tube.

I can't believe I missed that. At least this is a relatively easy fix. Many thanks!

 

[Paul Birkeland]

Once you get the octal socket reoriented, be sure to remeasure your voltages.  I suspect that terminal 1 will still be too high.  If it is, other voltages in the amplifier will also be higher than they should be, but you will want to focus on terminal 1 and ignore the rest of them until you see 70-90V there. 

High voltage at T1 on a stock Crack means that you should check to see that both halves of the 12AU7 are glowing, that both the LED's are properly installed, that the ground jumper is present on the volume pot, and reheat all the solder joints on the 9 pin socket and terminals 1-5.

-PB

 

[Sixth.Gear]

Got everything de-soldered and turned, and then resoldered. All voltages check within 10-15%, and terminal 1 coming in at a spot on 81. Both halves of the 12AU7 and 6080 are glowing happily away.

Not quite out of the woods however. Right channel has a very loud hum that does not change with volume. Left channel is not audible at lowest volume setting, and will come in with a slight hum as volume increases. As I continue to increase volume, not much volume is increased on the right channel and the hum does not change in volume level. Right channel sounds clear as day and absolutely spectacular. Any ideas as to where this hum would be coming from?

Edit: Tried powering the Crack off with headphones plugged in, hum goes away instantly. Powered up with headphones in, no buzz and both channels work perfectly. Slight and extremely faint static still remains on the right channel that comes and goes in intensity, not changing with volume.  Is this sign of a bad ground somewhere?

 

[Paul Birkeland]

This sounds like a flaky solder joint and/or a loose component in the amplifier.

 

[Sixth.Gear]

Just went through all the connections as well as re-seated both tubes. Noticed the 12AU7 had one pin slightly bent, gently straightened it and re-installed. No hum detectable, so I'm wondering if it was the bent pin or something else.

Long story short, thank you for the help!

Even after only a few listening hours, there is no comparison in the increase in audio quality from my E17. I can't get over the difference. Can't wait to see what the speedball does after a few weeks of burn in on the stock Crack!