Help with voltage [resolved]

[kill_surf_city]

Do both halves of the 12AU7 still glow?  Your voltages tell me that one half is not conducting.

Do not listen to an amp that hasn't passed its voltage checks.  Those tell you whether or not the amp is working properly, and an amp that isn't working properly can destroy headphones.  (In fact having the 100uF cap in backwards will melt one headphone driver if you tried to listen to the amp like that, if you put a bulged cap back in and attempted to listen to the amp, you may have already caused some damage)

Do you think the cap needs replacing? That’s what I’m thinking since I seem to be having the voltage problem with the left side (Terminals 5 and 9). Also I only listened to it after I had put the bulged cap in properly. I’ve listened to my headphones since with my other amp and there doesn’t appear to be any damage.

 

[Jameson]

You could post more pictures of the cap and the rest of the build. If you don’t have a way to test its capacitance you could just buy a new one since they’re not super expensive.

 

[kill_surf_city]

You could post more pictures of the cap and the rest of the build. If you don’t have a way to test its capacitance you could just buy a new one since they’re not super expensive.

Here’s some pics

 

[Jameson]

I’m not an expert at this at all, so maybe PB disagrees, but I’d replace that cap before I ran electricity through the amp again.

 

[kill_surf_city]

I’m not an expert at this at all, so maybe PB disagrees, but I’d replace that cap before I ran electricity through the amp again.

That’s what I was thinking. Ordered a couple new ones last night from Mouser. Thanks!

 

[Paul Birkeland]

Yes, that cap is damaged.

 

[Paul Birkeland]

You can run the amp with no 100uF cap to continue debugging the issue you're having up front with those DC voltages that aren't correct.  Do both the LEDs on the 9 pin socket illuminate still?  At least one must be lit, but perhaps not both?

 

[kill_surf_city]

You can run the amp with no 100uF cap to continue debugging the issue you're having up front with those DC voltages that aren't correct.  Do both the LEDs on the 9 pin socket illuminate still?  At least one must be lit, but perhaps not both?

I have both the caps in right now. I’m gonna remove the bad one. But as of right now, neither LED comes on. I think one comes on initially then fades out.  But I’ll have to let you know for sure.

 

[kill_surf_city]

You can run the amp with no 100uF cap to continue debugging the issue you're having up front with those DC voltages that aren't correct.  Do both the LEDs on the 9 pin socket illuminate still?  At least one must be lit, but perhaps not both?

Okay, so as it stands with the cap damaged cap still in, the LED connected to A8 initially turns on when I plug it in then fades out. The other LED stays off. What should I look for?

 

[Paul Birkeland]

The LED should not turn on when you power up the amp.

Does this also happen with no tubes in the amp at all?

Can you post a fresh photo of just the 9 pin socket wiring?

 

[kill_surf_city]

The LED should not turn on when you power up the amp.

Does this also happen with no tubes in the amp at all?

Can you post a fresh photo of just the 9 pin socket wiring?

When I take the tubes out the LED doesn't turn on at all. Here’s pics of the sockets as well. I’m about to take out the bad capacitor.

 

[Paul Birkeland]

On the 9 pin socket, it looks like maybe the end of the LED going to A8 is touching the wire at A7. 

On the 8 pin socket, it looks like some of the ends of the green wires need to be trimmed that are sticking out. 

Do both halves of the 12AU7 still glow when the amp is running?

 

[kill_surf_city]

On the 9 pin socket, it looks like maybe the end of the LED going to A8 is touching the wire at A7. 

On the 8 pin socket, it looks like some of the ends of the green wires need to be trimmed that are sticking out. 

Do both halves of the 12AU7 still glow when the amp is running?

I’ll get to trimming! Also, yes both halves the the 12AU7 still glow. I have removed the bad cap.

 

[Paul Birkeland]

Can you also carefully measure the voltages at A3 and A8?

 

[kill_surf_city]

Can you also carefully measure the voltages at A3 and A8?

A3 - 02.7

A8 - 01.9

 

[kill_surf_city]

Can you also carefully measure the voltages at A3 and A8?

Also after doing the trimming I’ve gotten terminal 9 to come down to 115-116 and terminal 5 down to 92.1

 

[Paul Birkeland]

A3 - 02.7

A8 - 01.9

And they aren't glowing?!

I suspect that you have many cold solder joints.  If I had this amp on the bench for repair, I would reheat each one and let the solder flow out again. 

 

[kill_surf_city]

And they aren't glowing?!

I suspect that you have many cold solder joints.  If I had this amp on the bench for repair, I would reheat each one and let the solder flow out again.

The tube is glowing on both sides yes. But neither LED is lighting up. So are you saying i should re-solder the joints where the LEDs are connected?

 

[kill_surf_city]

And they aren't glowing?!

I suspect that you have many cold solder joints.  If I had this amp on the bench for repair, I would reheat each one and let the solder flow out again.

Ok I resoldered the joint on the LEDs and got A8 to light up but broke A3 in the process. Something tells me that the A3 LED wasn’t in there very well to begin with. So I’ll have to order a new LED for that joint unless there’s some kind of work around for that. Thanks Paul!

 

[Paul Birkeland]

You can install a wire jumper between A3 and A8.

I would resolder all of the joints in the amp, not just the ones where the LEDs connect.