Speedball Troubleshooting - High OA/OB values

[Justin]

I appreciate the help.

[Paul Birkeland]

I would go back to the 22K resistors instead of the small PC board, then continue debugging the circuit.  The issue you're experiencing is likely something iffy with the underlying build.

[Justin]

Alright. I'll have to order some new ones and get back with you later on. Thanks

[Justin]

Oooookay. New 22.1K resistors in place of the small board. I retraced every step in the instructions from point to point (I'd be surprised if it were miswired at this point but foolish to rule it out), and carefully inspected and re-soldered any joint that I didn't like. During this process I found a couple of wires i'd attached to a lower terminal that i went ahead and corrected to the upper as the instructions called for or visa versa, but nothing that I think would affect the current. Right now my resistance and voltage terminal checks are as follows:

Resistance     Voltage
1. *                131.5V
2. *                186
3. 0                    0
4. *                184.5
5. *                124.7
6. 0                    0
7. Over Limit   144
8. 0                    0
9. Over Limit   140
10. 0                  0
12. 0
13. *
14. 0
20. 0
22. 0
B3. Over Limit
B6. Over Limit
RCAs in spec

I can provide any other measurements or pictures as necessary. Any ideas?

 

[Paul Birkeland]

I am going to guess that your LEDs on the 9 pin socket aren't lighting.  When you look at the 12AU7 with the amp on, do both halves of the tube glow?

[Justin]

No, both LEDs on the 9 pin light up fine and both halves of the tube glow.

[Paul Birkeland]

Can you post some new photos?  I suspect that one of the black wires that makes up the ground buss isn't well connected.

Can you also measure the voltage at A2 and A3 again carefully?

[Justin]

A2 is 0, A3 is still 1.58V.

[Justin]

Figured it better to give you too many than not enough

[Deke609]

What is that gray metallic wire crossing the amp that ends near the green heater wiring on the transformer? Is that your solder?  If so, and based solely on its diameter, it looks a lot like plumbing solder not electronics solder. 

[Paul Birkeland]

Plumbing solder would cause strange things like this to happen.  I'd also love to see a photo or two of your 12AU7, which sounds strange, but it's good to be sure.

[Justin]

No, the soldier is 60/40 rosin core for electronics. I'm not sure what you're needing to see with the 12UA7 pics but heres a few - let me know if you wanted to see a different angle. It came in an old RCA box with the amp, and I've tried a few others which will alter the high voltages slightly but not to within spec.

[Paul Birkeland]

Well, that's not a 12AU7...

If it came from us, it might've snuck into a 12AU7 box on accident.

(I feel less crazy now BTW)

[Justin]

Oh wow, okay. Then the others I swapped in were all 12AT7 equivalents as well maybe. The 5963, ECC83, and CV4024 I tried would just give me similar values to the 12AT7 I started with, right? I guess I don't have a true 12AU7 here to check if that fixes it. I'll let the forum know if that solves my issue when I get the right tube, but I gotta say it feels good to know you think that's it, Paul. I've got 98 extra 22.1k resistors with your name on them if you want them!

[Paul Birkeland]

The 5963

This is a 12AU7

, ECC83,

This is not a 12AU7

and CV4024

This is not a 12AU7

You need to run the amp with the 5963/12AU7.  The other tubes will destroy the amp.  The other tubes you are trying are absolutely not compatible with the Crack.