Nobelium - tube bass preamp project

[Tassieviking]

Hmmmmm.......I have never seen a 12AX7 tube used for V1 neither, and I think the XLR PCB is back to front as well from what I can see.
If I had seen this on April 1st I would have thought it was a joke, come to think of it it is a joke since absolutely nothing is correct

 

[vigilante398]

Hmmmmm.......I have never seen a 12AX7 tube used for V1 neither, and I think the XLR PCB is back to front as well from what I can see.
If I had seen this on April 1st I would have thought it was a joke, come to think of it it is a joke since absolutely nothing is correct

Exactly. It's one of those "the longer you look, the worse it gets" things.

 

[Schmavirz]

Wondering if anyone can help me. This is my first project. both xlr and 1/4” out and tone controls work, tubes heat, everything is good except for the LED on the left board. When I measure voltage on the positive leg of both LEDs I get the same value, I can’t for the life of me figure out why led on the right lights and the left doesn’t.

Any suggestions on how to troubleshoot this?

 

[chongmagic]

Wondering if anyone can help me. This is my first project. both xlr and 1/4” out and tone controls work, tubes heat, everything is good except for the LED on the left board. When I measure voltage on the positive leg of both LEDs I get the same value, I can’t for the life of me figure out why led on the right lights and the left doesn’t.

Any suggestions on how to troubleshoot this?

I would first double check that the LED polarity is correct, and that the LED itself is actually good. If the LED is oriented correctly, try reflowing the pins from the tube board to the main board and confirm continuity between the boards.


If you're seeing voltage on the LED positive leg but it isn't lighting, it usually means either the LED is bad, installed backwards, or the ground leg doesn't have a good connection.

 

[Schmavirz]

I would first double check that the LED polarity is correct, and that the LED itself is actually good. If the LED is oriented correctly, try reflowing the pins from the tube board to the main board and confirm continuity between the boards.


If you're seeing voltage on the LED positive leg but it isn't lighting, it usually means either the LED is bad, installed backwards, or the ground leg doesn't have a good connection.

The ground legs both show the same reading too, (different from the +, but the same LED to LED), and this LED works when inserted into the right board.

 

[Schmavirz]

Nevermind, was measuring wrong, it gets no power. I have reseated everything on the board, but still nothing.

However the Tube heats up and the nobeliun functions as expected. Any advice? Should i try to get a new tube board, socket, snd 2x5 connector and redo everything? Is it insane to swap the left and right tube boards to see if that makes a difference on the left side?

 

[TillMack]

No. Just change the Led. Long leg to plus and shorter leg to minus.

Edit: sorry, don’t checked your second post.
Forget what I say.

 

[vigilante398]

Nevermind, was measuring wrong, it gets no power. I have reseated everything on the board, but still nothing.

However the Tube heats up and the nobeliun functions as expected. Any advice? Should i try to get a new tube board, socket, snd 2x5 connector and redo everything? Is it insane to swap the left and right tube boards to see if that makes a difference on the left side?

Check R4, the 1k CLR resistor next to the left tube board. Make sure it's a 1k and not something higher. Also check the solder joints on the pins and on the connections of the board itself.

 

[Tassieviking]

The top of R4 should be connected to ground on the PCB, then it goes from the bottom of R4 to the two right hand side pins of the tube risers to the Tube PCB, from there it goes to the round negative pad of the LED itself, the positive leg of the LED goes to pin 5 of the tube which is the positive leg of the tube heater.
The other tube is identical except it uses R6 to drop the voltage to the LED.
If you compare the bottom of R4 and R6 they should be approximately the same voltage, the top of R4 and R6 should be at 0V.
Check to see if the right side pin headers that hold the Tube PCB up connect to the round negative pad of the LED as well, there could be a track broken there, there could also be a track broken between the bottom of R4 and the pin header.