Old design (2015) new build fail at voltage test (fuse blows) [resolved]

[goldencalves]

Hey, I bought this kit in late 2015 and finally carved some time out a couple months back to assemble it.  I got together, double and triple-checked, and the resistances check out pretty well.  Once I get to the voltage check the fuse blows whenever give it power.  I've gone through a handful of fuses.  I've re-melted any solider that looks suspect.

The only thing I did differently from the standard 2015 instructions was the page 19 "Revision 5/6/10:
Making this wire 3” long and connecting it to Terminal 14U instead of terminal 22L may yield more quiet operation."

Can anyone spot anything definitely out-of-place?  I am a moderate-nube at this sort of thing.

Thanks!

 

[Paul Birkeland]

Are the leads of the UF4007 diodes under the black wire in the red circle touching each other?  If so, you'll blow fuses indefinitely until you spread them apart.

You have one black wire on your headphone jack that doesn't look to be soldered.

 

[goldencalves]

Thank you for your response!  I just saw this now, I think I missed an email notification.

You are correct!  The UF4007 diode leads are touching each other.  I'll spread them and plug everything in soon and see how that changes the situation and update this post. 

The headphone jack wires appear to be soldered; it must be a bad pic.  Thanks again for looking at this and assessing! 

 

[goldencalves]

Spread those diode leads, triple checked all solders, plugged everything in, fuse still blew.  Any other possibilities? 

 

[Paul Birkeland]

What kind of fuses are you using?

 

[goldencalves]

500 ma, but I think I used a few 1 amp fuses as well

 

[Paul Birkeland]

500mA isn't going to do the job.  1A fast should hold, but there's no harm in getting a 2A fuse just to be sure.

-PB

 

[goldencalves]

Thats the ticket!  I was using .5 because I thought that was what they packaged with the Crack.  2 amp is holding fine.

The problem now: the large tube (6080/6AS7) is glowing well, but the smaller tube (12AU7) is not.  The 12AU7 is getting warm, but emanating no glow even after a couple of minutes.  One of the LEDs connected to its socket is lit up (A3), and the other is not (A8). 

I just took a few readings before disconnecting; most seemed normal, but Terminal 1 read at 153 (instead of 75-90). 

 

[Paul Birkeland]

If you have 153V at terminal 1 but a proper voltage at terminal 5, then at least half of the 12AU7 is heating.  To get to the root cause, it would help to know what the DC voltage is at pin A8.

 

[goldencalves]

81 @ terminal 5, 13 @ A8

 

[Paul Birkeland]

Your LED at A8 is damaged, which can happen if they are stored for a long time or resoldered after they have been sitting around.  A remedy for this particular issue is to connect a wire jumper between A3 and A8. 

-PB

 

[goldencalves]

Paul-

Big thanks!  I had some spare LEDs laying around, so resoldered one (actually two; I shorted the first replacement somehow) and they're both glowing, got all the voltages tested within the tolerances, everything is working great! I definitely would have been putzing around with this indefinitely without the assistance.  Thanks again so much! 

;D