denti alligator
New member
Big board
bA 0
bB 0
A +reg 310 and dropping
B + reg 305 steady
A1 384
B1 382
OA 303.8
OB 305
bA 0
bB 0
A +reg 310 and dropping
B + reg 305 steady
A1 384
B1 382
OA 303.8
OB 305
Right channel noisy. Help troubleshooting
- Thread starter denti alligator
- Start date
denti alligator
New member
Little board
OA 239.5
OB 301.5
1A 304.9
1B. 303.8
OA 239.5
OB 301.5
1A 304.9
1B. 303.8
Ok, that narrows things down a bit. The regulator seems to be doing its job, but the OB on the small board tells us that the driver half of one 12AT7 isn't drawing any current. This could be a loose resistor on pin 3 of the 9 pin socket under the small board, a bad solder joint on the small board (it doesn't matter if it has been working for x many months/years, it can still happen), a broken wire, or a loose resistor going to pin 2 on that same socket.
denti alligator
New member
OK, I reflowed 2 and 3 on the 9-pin. The LEDs for B on the small board are not lit up. What else can I try?
denti alligator
New member
I tried switching the 12AT7 tubes. Now the LEDs all light up. Maybe one of them wasn’t in right?
Voltages for small board are not even:
1A 354
1B 303.7
OA: 285.7
OB: 244.4
I also reflowed all connections on the small board
Voltages for small board are not even:
1A 354
1B 303.7
OA: 285.7
OB: 244.4
I also reflowed all connections on the small board
If plugging and unplugging the tubes is causing huge changes, you have loose socket connections (or something connected to a socket is not well connected at its other end).
denti alligator
New member
Sockets are very very tight.
It's not the sockets, it's that something connected to the socket pins is loose or not well soldered.
denti alligator
New member
I’ll reflow all the pins. But here’s something weird. I switched the tubes again and the LEDs, went out. So I switched them back and they’re back on. ??
denti alligator
New member
I reflowed all the pins. Can you tell me what readings I’m supposed to get on the boards? I’ve still got a discrepancy between A and B.
(And I’m starting to despair.)
(And I’m starting to despair.)
OA and OB on the big board should be just a bit over 300V.
OA and OB on the small board should be around 200V.
OA and OB on the small board should be around 200V.
denti alligator
New member
Readings on the big board have changed:
OA: 380
OB: 348
Small board
OA: 289
OB: 246
Does the odd reading at 14 not tell us anything?
Also, the consistency with which those B LEDs go out when I switch the tubes has me troubled. If it were a matter of something loose, wouldn’t it not be coinsistent? Again, the B LEDs only light up with one of the tubes—the same tube.
Could it be that one of the tubes is bad?
OA: 380
OB: 348
Small board
OA: 289
OB: 246
Does the odd reading at 14 not tell us anything?
Also, the consistency with which those B LEDs go out when I switch the tubes has me troubled. If it were a matter of something loose, wouldn’t it not be coinsistent? Again, the B LEDs only light up with one of the tubes—the same tube.
Could it be that one of the tubes is bad?
14 is wired to OB on the small board.
The pair of high voltages on the big board indicate loose connections and/or broken wires.
You have loose connections or broken wires.
The high voltage at OA on the small board are a different loose connection or broken wire that's likely unrelated to the bigger regulator board's issue.
The pair of high voltages on the big board indicate loose connections and/or broken wires.
You have loose connections or broken wires.
The high voltage at OA on the small board are a different loose connection or broken wire that's likely unrelated to the bigger regulator board's issue.
denti alligator
New member
OK, thanks. How would suggest trying to track this down? Systematically reflowing all connections on the left side? I did the board, but not the resistors and transistors on it. I guess I can reflow those, too.
Can you explain why switching the tubes makes the LEDs lights not light up?
Can you explain why switching the tubes makes the LEDs lights not light up?
denti alligator
New member
Well, I’m leaving town for a week and won’t be able to work on this till I return. A little tomorrow morning, if you have any last-minute suggestions.
Here’s what I’ve done:
Reflowed (and in some cases added new solder) to
- All 9 pins of left channel tube, including center pin.
- Terminals 14 (top), 16 (top and bottom), 36 (top and bottom), 12 (bottom), 11 (top), 34 (top and bottom), and probably more.
- All wire connections to small board
- reflowed transistor leads on B side of small board
- all wired connections to big board
Checked all wires and leads going to left 9-pin socket. No nicks or breaks or interferences.
I don’t know what else to do.
Note that I get different readings when I switch the tubes, and I also get LEDs lit up with ones but not the other. This goes *with the tube*, but doesn’t affect the LEDs when I move it to the other side. The readings, though, are consistent.
ONE WAY:
Small board:
No B LEDs
OA 233
1A 305
1B 304
OB 301
Big board:
OB 305
1B. 389
OA 303
1A 388
OTHER WAY:
Small board:
B LEDs are lit up
OA 291
1A. 347
OB 242
1B 304
Big board:
OB 325
1B 387
OA 303
1A 389
If I didn’t know better (and I don’t!) I’d say there’s a problem with one of these tubes.
Here’s what I’ve done:
Reflowed (and in some cases added new solder) to
- All 9 pins of left channel tube, including center pin.
- Terminals 14 (top), 16 (top and bottom), 36 (top and bottom), 12 (bottom), 11 (top), 34 (top and bottom), and probably more.
- All wire connections to small board
- reflowed transistor leads on B side of small board
- all wired connections to big board
Checked all wires and leads going to left 9-pin socket. No nicks or breaks or interferences.
I don’t know what else to do.
Note that I get different readings when I switch the tubes, and I also get LEDs lit up with ones but not the other. This goes *with the tube*, but doesn’t affect the LEDs when I move it to the other side. The readings, though, are consistent.
ONE WAY:
Small board:
No B LEDs
OA 233
1A 305
1B 304
OB 301
Big board:
OB 305
1B. 389
OA 303
1A 388
OTHER WAY:
Small board:
B LEDs are lit up
OA 291
1A. 347
OB 242
1B 304
Big board:
OB 325
1B 387
OA 303
1A 389
If I didn’t know better (and I don’t!) I’d say there’s a problem with one of these tubes.
You can certainly put a new pair of tubes on order, but I wouldn't be super convinced that this will take care of all the issues. Still, it would be helpful to reduce some variables in the process.
denti alligator
New member
Alright, I’ve ordered a new pair which should be here when I get back home in a week.
Assuming the problem persists in some fashion:
Is there anything I can do to narrow down the source? See the list of what I’ve done above.
Assuming the problem persists in some fashion:
Is there anything I can do to narrow down the source? See the list of what I’ve done above.
I may be way off base here, and I don't own a Stereomour II. But I seem to remember reading something PJ wrote about the 12AT7 in the amp. I think he said one triode in the tube was the voltage amplifier. So being the efficient engineer he is the left triode is used in the left tube and the right triode is used in the right tube, or visa versa. So on the base amp without shunt regulation when you wear out the 12AT7 you could swap left for right and start using the fresh triode in each tube.
If this really is the case maybe one triode in one of your 12AT7s is bad and swapping them put the working triode in the gain position. Of course if you do have the shunt regulation upgrade it would also mean the bad triode is now doing SR duty and that is not working properly. If that is the case a new tube or pair of tubes should fix the problem.
Paul, if this is totally wrong and would only confuse others who read it please delete this post.
If this really is the case maybe one triode in one of your 12AT7s is bad and swapping them put the working triode in the gain position. Of course if you do have the shunt regulation upgrade it would also mean the bad triode is now doing SR duty and that is not working properly. If that is the case a new tube or pair of tubes should fix the problem.
Paul, if this is totally wrong and would only confuse others who read it please delete this post.
Paul Joppa
Moderator
kgoss said:
I don't think that is totally wrong, though there are some indications of further issues. Trying some fresh tubes will help answer that question.
denti alligator
New member
Thanks, Ken. I do have the shunt regulator installed. I’m curious to see what happens when I try the new tubes. I’ll report back in about a week.
