Build done. Half-glow LED, wrong voltages, no 6080 glow

[pkb]

I can't say yet whether it has sound since the only pair of phones I have are HD650's and I'm afraid.

Here are my voltages (L) alongside the expected voltages (R) and the problem voltages in BOLD and UNDERLINED:

The voltages were measured grounded to T12. I tried to follow Doc's advice and measure from the terminal below the solder joint to test for continuity and wasn't able to find a joint that measured differently from lead, joint, or terminal.

Does anyone have any ideas? I'm going to continue looking for bad solder joints and hope. It'd be great if it was that rather than a bum tube or component.

Many thank-you's.
Patrick


1. 98 90
2. 210 170
3. 0 0
4. 210 170
5. 24 90
6. 0 0
7. 24 100
8. 0 0
9. 0 100
10. 0 0
11. 0 0
12. 0 0
13. 210 170
14. 0 0
15. 215 185

20. 0 0
21. 219 206

a1. 24 90
a2. 0 0
a3. 1.39 1.5
a4. 0 0
a5. 0 0
a6. 98 90
a7. 0 0
a8. 1.55 1.5
a9. 0 0

b1. 98 90
b2. 211 170
b3. 24 100
b4. 24 90
b5. 211 170
b6. 0 100
b7. 0 0
b8. 0 0

 

[pkb]

Addtional info as it continues to roll in:

The resistance between t4 and t5 moves slowly upwards, starting at negative 12k or so and creeping past positive 10k. I didn't wait around for the 5 minutes I'd guess it'd take to find its ceiling. On the other hand, t1 and t2 measure 22k solidly. No movement.

I pulled the 22k resistor between t4 and t5, measured it @ 22k, resoldered, and symptom is unchanged.

However, if I remove the 6080, the resistance between t4 and t5 measures correctly at 22k.

 

[pkb]

I may be fooling myself, but it looks like I share symptoms with this case: http://www.bottlehead.com/smf/index.php/topic,2001.msg15453.html#msg15453

I checked for a short between pins 3 and 4 on the actual tube, off the board, and lo--it appeared to be shorted.

 

[Grainger49]

I would suggest to go back to your first post and edit (modify) it so there is only the relevant information there.

You need only post the voltages that are more than 15% out of spec.  Post the voltage you read and what it was supposed to be as well as the point being measured.

That way the guys on the board helping you can address the problems and don't have to wade through 30+ voltages if just a few are off.

 

[pkb]

Completed. I kept the "in-spec" voltages to demonstrate that my line voltage is either high or whatever's going on is causing the voltage to be higher across the board.

Thanks

 

[pkb]

I borrowed a spare 6080 from a local electronics guy and replaced the "shorted" tube. Unless it, too, is shorted in the exact same way, I don't think the tube is the problem. The amp still has the same problems. The voltages haven't changed.

 

[Paul Joppa]

You said the tube doesn't glow, which means it is not getting heater voltage. None of the other voltages will make sense if that is the case.

You also found a short between pins 3 and 4, which seems unlikely since the connect to different triodes. Might you have made an error in the orientation of the socket? Pins 7 and 8 are 180 degrees rotated from 3 and 4, and 7-8 is the heater which has very low resistance.

 

[pkb]

HA!

The tube is wired 180 degrees backwards!

I'll rewire and report back.

Thank you!!!!

You said the tube doesn't glow, which means it is not getting heater voltage. None of the other voltages will make sense if that is the case.

You also found a short between pins 3 and 4, which seems unlikely since the connect to different triodes. Might you have made an error in the orientation of the socket? Pins 7 and 8 are 180 degrees rotated from 3 and 4, and 7-8 is the heater which has very low resistance.

 

[pkb]

The amp sounds good.

Really good.

 

[[email protected]]

Don't feel bad.  Done it a few times myself.  You're just sure that you are counting pins in the right direction and then, CRAP!  That just ain't quite right. 

Now-a-days I have to number the chassis with a felt tip pen and then go back and check to see if I did that right before I start anything.

I'm glad you got it worked out.  That Crack is one awesome amp.  Enjoy the fruits of your labor.

 

[Paul Joppa]

Dude - that was FAST! Glad it worked out.

 

[Grainger49]

If I told some of the bad mistakes I have made no one here would listen to me again.