Crack 1.1 Voltage/LED help [resolved]

[mobiusfun]

Hi,

I just wrapped up my Crack 1.1 kit tonight, and while the resistance checks were fine the voltage checks had the following inconsistencies (my values left, expected values in parentheses):

1. 165V (50-100V)
2. 115V (170V)
4. 115V (170V)
7. 147V (90-115V)

All other voltages were within spec.  Additionally, my A3 LED is much dimmer than A8.  Any ideas?

[Paul Birkeland]

Can you post all your voltages on terminals 1-10?

When I see a voltage at terminal 1 that's higher than the voltage at terminal 2, that would have me suggesting that one of the black wires in your amp is not well soldered.  Most commonly we find that where the two black wires meet on the headphone jack is a typical trouble spot, and I would be extra sure both of those wires are captured by solder.

If that is not the case, I would post some build photos when you get the chance.

[mobiusfun]

Thanks for the suggestion.  I reflowed the joint where the black wires meet at the headphone jack, but I'm still seeing the same voltages.  Here's the full list:
 
1.165.3V (50-100V)
2.115.2V (170V)
3.0V (0V)
4.114.8V (170V)
5.64.5V (50-100V)

6.0V (0V)
7.147.6V (90-115V)
8.0V (0V)
9.92.0V (90-115V)
10.0V (0V)

[Paul Birkeland]

The connection between B5 and B2 has not been correctly made.

Try fixing that, then recheck your voltages.

[mobiusfun]

You're absolutely right, I had mistakenly connected B5 to B1 instead of B2.  Fixing that made my voltages look much better:

1.84.7V
2.189.8V
3.0V
4.189.5V
5.0V

6.0V
7.61.6V
8.0V
9.115.7V
10.0V

T2 and T4 look a bit high, should I be worried? 

[Paul Birkeland]

You're absolutely right, I had mistakenly connected B5 to B1 instead of B2.  Fixing that made my voltages look much better:
5.0V
T2 and T4 look a bit high, should I be worried?

No, you should be worried about terminal 5 changing to 0V.

Other build observations:
1.  There's too much jacket stripped off the wire at B4. I would push more of the wire into B4 to prevent it from shorting to an adjacent terminal.
2.  There's too much jacket stripped off the red wire going into power transformer terminal 11.  If that wire touches the adjacent power transformer terminal, that will create a lot of problems.
3.  There's too much jacket stripped off several of the wires going to the volume pot.  Again, this can create shorts down the road that will cause your amp not to work.
4.  There's too much jacket stripped off the green wire going to A4/A5.  If this wire touches the chassis plate, it will destroy your power transformer.

[mobiusfun]

Sorry, that must have been a typo.  My voltage at T5 is 90V.  I'll make sure to rewire and/or insulate those connections that you mentioned.

Thanks a lot for the super responsive support!

[Paul Birkeland]

Can you recheck terminal 7?  Terminal 7 should have a higher voltage than terminal 5.

[mobiusfun]

I rechecked T7, and yes, it is still around 62V.  Interestingly the A8 led is now off, where before it was A3.

However, I messed up.  When I was rechecking the voltage, I accidentally caused a short with my probe between B2 and B1, I believe (possibly B3 and B2).  There was a spark, and now I'm seeing these voltages:

1. 0.2V
2. 189,9V
3. 0V
4. 190V
5. 89.4V

6. 0V
7. 62V
8. 0V
9. 115.8V
10. 0V

I'm pretty upset with  myself.  Any idea what I damaged?

[Paul Birkeland]

Can you pull the 6080 and recheck the voltages on terminals 1-5?  It's really weird to have 0V on terminal 5.  The 0V on terminal 5 will cause the LED to not be lit, but be aware that a defective LED can't cause this problem, so you can leave it alone.

Also can you post the voltages on terminals 1-5 with no tubes at all in the sockets?

[mobiusfun]

Sure, however I'm not currently seeing 0V at T5.  That was a typo - I should have reported 90V.  It was T1 that went to 0V after I shorted something in the octal socket.  Here are my voltages with just the 6080 tube pulled:

1. 0.2V
2. 238V
3. 0V
4. 238V
5. 101.3V

6. 0V
7. 0V
8. 0V
9. 0V
10. 0V

And with both tubes pulled:

1. 0V
2. 245.3V
3. 0V
4. 245.3V
5. 244.5V

6. 0V
7. 0V
8. 0V
9. 0V
10. 0V

[Paul Birkeland]

The 22.1K resistor between 1 and 2 is either loose on one end or it's open. 

[mobiusfun]

You're right.  In my desperation to fix this, I had apparently "trimmed a lose end" at T2 and completely cut off the lead of the resistor there.  It looks like I'm going to need to order a new resistor, but I was able to get solder the nub to a piece of bus wire, then to the terminal.  With that, I got these voltages, all apparently within spec:

1. 84.9V
2. 176.8V
3. 0V
4. 176.9V
5. 85.2V

6. 0V
7. 108.4V
8. 0V
9. 108.9V
10. 0V

Looks like I didn't break anything with my short, after all, but I'll certainly be more careful in the future.  And it does serve to drive home that point about needing to add more insulation.  I'll order a new resistor and clean up those connections you mentioned.

[Paul Birkeland]

Those look like good working voltages.

You can paint over those bare wires with liquid electrical tape or nail polish in a pinch if necessary. 

[mobiusfun]

Good to know, thanks.

Just did a listening test now that I'm finally able to plug some phones in and I'm impressed!  Hell of an amp you designed, Paul.  Thanks again for all the help you provided to get it working.