Crack stopped working, low output on one ear and none on the other

[blyn]

Hi everyone,

After about half of year of enjoying my crack/speedball I've run into some issues.  I accidentally left it on overnight and when I came back to it i started having problems.  It ran fine for a few minutes, maybe outputting a little less than usual, and then suddenly switched to the state it's in now: very little output on the left side and none on the right. 

I ran through resistance checks, everything still seems fine.  Voltage is a different story - everything's low across the board and a few readings are very off. Here's what i got:

• 1: 7
• 2: 64
• 3: 0
• 4: 69
• 5: 65
• 6: 0
• 7: 0.1
• 8: 0
• 9: 56
• 10: 0
• 11: 0
• 12: 0
• 13: 62
• 14: 0
• 15: 128
• 20: 0
• 21: 196

I double checked the voltages when i was done, maybe about a 5 minute difference, and noted that i was getting some variable readings.  1 read 5V and 5 was 54V for example, I didn't check any more.

Any thoughts?  I'm looking forward to hearing your thoughts, I'm listening to music through my backup solid state amp right now and it feels like something is missing.  Thanks!

 

[Paul Birkeland]

Look for shorts between pins on the tube socket pins or adjacent terminals.

The 0V on T7 would make me think that you have a TIP50 touching the heatsink, but that doesn't explain the 7V at terminal 1.

Can you run the amp without the 6080 and remeasure the voltages at terminals 1-5?

-PB

 

[blyn]

Alright, some strange behaviour.

First i checked the voltages without the 6080, i got these: 71, 231, 0, 231, 68 (for 1 to 5).  I checked the TIP50s and the heatsinks, seems like nothing is touching there.

Then i noticed that some of the LEDs weren't lit: the one between the center terminal and A8, and two on the big speedball board at the back.  So i checked for shorts a bit, saw something maybe a bit suspicious between A8 and A9 so i moved A8 a touch (edit, A7 and A8 actually).  Powered the crack back on after this and i saw/heard a bit of a spark within the 6080 tube.  Checked voltages again after this and suddenly we're back to normal - from what i can tell all of the voltages are fine now.

 

[Strikkflypilot]

The spark may have come from a loose particle in the 6080. Scared the hell outta me once.

 

[blyn]

Strange.  I do hear something rattling inside my 6080.

Somehow it looks like my 12AU7 ended up cracked - the glass shattered near the top.  I suppose it could have been hit when i was flipping the chassis over.

Anyways, I was looking to get new tubes at some point anyways so i guess i'll look into replacing these.  But let me know if any of this still sounds concerning of being a fault in the circuit.