2A3 tube problem in Stereomour II [resolved]

[Omegabuzz]

Hi,

I think I have a problem with one of the 2A3 tubes in my Stereomour II.

I received the kit on July 10, 2023. The order includes all the option for the Stereomour II, the Shunt Regulator, the DC filament and the MourQuiet Stepped Attenuator.
 
I build the Stereomour II first and everything was fine. I listened the amplifier for 3 days. After I added the DC filament and everything was fine. I listened the amplifier for 3 days. After I added the Shunt Regulator. I listened the amplifier for 5 days. Finally, I added the the MourQuiet Stepped Attenuator.

For me, each of the options added greatly improves the sounds.

Over time, I found that left channel was not at the same level as the right channel. The problem was more significant after 3 hours of listening.
I exchange the tube left-right, and the problem follows the defect tubes. Also, the elements of the tubes that has the problem is not as bright as the tube that works fine. The level could be fine when I turn on the Stereomour II, but after sometimes, the level drop now by 50%.

Is there any tests that I could do to confirm the problem with the tube?

I include photos of the inside of the Stereomour II.   

This is the result of the all of the verifications.

The resistance check was OK.

Hum adjustement OK.

Voltage check after building the Stereomour II
1. 371,1 VDC
2. 400,1 VDC
3. 0 VDC
4. 0 VDC
5. 0 VDC
6. 60,2 VDC
7. 211,8 VDC
8. 0 VDC
9. N/A
10. 0 VDC
11. 0 VDC
12. N/A
13.  0 VDC
14. 227,1 VDC
15. 58,9 VDC
16. 0 VDC
17. 0 VDC
18. 0 VDC
19. 398 VDC
20. 371,1 VDC
21. 60 VDC
22. 60,8 VDC
23. O VDC
24. 60,6 VDC
24. 60,2 VDC
25. 60,2
26. 0 VDC
27. 399,8 VDC
28. O VDC
29. O VDC
30. 406,3
31. 406,2
32. not check
33. not check
34. 392,2 VDC
35. O VDC
36. 58,7 VDC
37. 59,1 VDC
38. 0 VDC
39. 58,8 VDC
40. 58,6 VDC
41-45. not check

Voltage check after DC filament supply installation
A1-A4. 2,5 VDC
D1-D4. 2,55 VDC

Voltage check after Shunt Regulator installation
IA. 390 VDC
OA. 299 VDC
KregA. 3,8 VDC
IB. 391 VDC
OB. 303 VDC
KregB 3,5 VDC

Thanks for your help!
Yves

[Thermioniclife]

Did you try swapping the 2a3 tubes and see if the problem follows the tube? And also the driver tubes? Plus double check the resistors on the stepped attenuater.

[Omegabuzz]

Hi Lee,

Yes, I swapped the 2A3 and the problem follows the tube.

This morning, I turned on the amplifier and no sound from the left, the tube with the problem. I swapped again and the problem follows the tube. Now, the tube with the problem is completely dead, no light and no sound.


Thanks for your help.

Yves

[Paul Birkeland]

You would want to post the voltages at pins 1, 2, and 4 on each 4 pin socket once the difference in channels appears. 

[Omegabuzz]

Hi Paul,

This morning I turned on the amplifier and the defect 2A3 tube is now completely dead, no sound. I swapped the tube and the problem follows the defect 2A3.

One of my friend will lend me a matched pair of 2A3 Electro Harmonix for testing.

Thanks for your help.

Yves

[Paul Birkeland]

You may find that soldering the tips of the fatter pins on the tube may restore it to operation.  You'll want a very hot iron for this, and to add as little solder as possible to the very tip of each of those pins to get them hot enough for the solder to flow out a little more.

[Omegabuzz]

Hi Paul,

Is the warranty on the tube will be void if i’m trying to do that?

Just for your information, I received the Stereomour II on July 10 2023 and the tubes should be cover by the warranty of Bottlehead. The tubes, Pvane 2A3, played less than 100 hours.

Thanks again for your help.

Yves

[Paul Birkeland]

It won't hurt to attempt the soldering.  It's possible that the wire inside the pin is touching the solder but didn't get completely captured by it.  Reheating the fat pins will allow the solder in there to flow out again and may fix the issue.

[Omegabuzz]

Hi Paul,

If there no problem for the warranty, I will try to do that tomorrow morning. I just checked a video on YouTube on how to repair bad connections on tubes pins. I have a good desoldering station to remove the bad solder at the end of the pin and put new one my soldering station.

Also, my friend lend me tonight the match pair of Electro Harmonix 2A3 to test the amplifier and everything is working fine with these tubes.

Stay tune for the next post tomorrow.

Thanks again.

Yves

[2wo]

Don't try to remove the existing solder, just use a good hot iron to heat the pin then add a small amount of solder to the hole in the pin tip...John

[Omegabuzz]

Hi,

I followed Paul's advice and redid the contacts on the fatter pins of the defective 2A3 tube. I noticed that one of the contacts had hardly any solder. Before redoing the welds, I use the multimeter and compare the good tube with the bad one and there was no continuity between the fatter pins. Since the quality of the welds meant that the contact was not optimal, I decided to redo them for the 4 pins of the defective tube. I tested the tube and it worked perfectly. Based on this experience, I decided to redo the welds on the functional tube. The contacts were better, but there was still very little solder.

Now both tubes are illuminated with the same intensity. Also, after listening for one hour, I think the sound is greatly improve. To test the proper functioning of the tubes, I will let the amplifier run for the next 24 hours. But for now, I think the problem is solved.

Thanks to Paul and the Bottlehead community for helping me fix the issue.

Yves

[Paul Birkeland]

Excellent work!

[oztayls]

You may find that soldering the tips of the fatter pins on the tube may restore it to operation.  You'll want a very hot iron for this, and to add as little solder as possible to the very tip of each of those pins to get them hot enough for the solder to flow out a little more.

Wow, I've never heard of that little trick! Great advice to keep in mind. I've probably thrown out some good tubes in the past that had the same symptoms. Thank you.