Uh oh. Load buzzing from headphones

[CORedhawk]

All has gone well with my new C2A until I came back to listen after the unit was on for a couple of hours. Now there is a loud buzzing coming from the headphones - both left and right. I'd appreciate any guideance.

Thanks!

[Doc B.]

Most likely a bad ground connection. Pull your headphones and recheck your voltages first. Post any reading that is off spec here. Also inspect your solder joints and reflow any that look suspect.

[CORedhawk]

Here are the readings Doc. OB on the low current board and OB on the left high current board are now lower than originally tested.

Low Current C4S

IA 149.9
OA 72.4
KregA 4.1
bRegA 149.9
iB 149
OB 45.3
KregB 4.8
bRegB 149

High Current C4S - right, left

IA 187.7        188.2
OA 149.9        149
bA .4              .2

IB .4               .2
OB 95.4          76
bB 149.8          148.9

[Paul Birkeland]

There's something not right with the 12AU7 portion of the amp.  Typically when I see 45V at one of those output terminals, that would be a backwards transistor.  Still, does that voltage move with no 6080 and 6AQ5 tubes in the other sockets?

[CORedhawk]

There's something not right with the 12AU7 portion of the amp.  Typically when I see 45V at one of those output terminals, that would be a backwards transistor.  Still, does that voltage move with no 6080 and 6AQ5 tubes in the other sockets?

Removed all buth the 12AU7 and tested voltages:
 Low current OB is 74
High current OB is 1.38

[Paul Birkeland]

Now return the 6080 to the amp and recheck.

[CORedhawk]

Now return the 6080 to the amp and recheck.

Paul:

Low voltage board 75
High voltage 112.2

[Paul Birkeland]

See if the problem comes back with the 6AQ5s now.  (It would be odd if it did)

[CORedhawk]

See if the problem comes back with the 6AQ5s now.  (It would be odd if it did)

Paul - put the 6AQ5s in now and it play beautifully. Can you help me understand what happened? Thanks! Doug

[Paul Birkeland]

Either you have a loose connection in the amp that you haven't found, or a dirty pin on a tube that is now clean from being pulled out an reinserted.

[CORedhawk]

Thanks Paul.

[Mucker]

Nice troubleshooting. I'll add that if you are getting even low hum or other noises, IME it's always a good idea to start at the pins. I've had tubes where the pins look ok, but after giving them a good cleaning, the noise disappears. Getting rid of a transparent layer does indeed help.

[CORedhawk]

Nice troubleshooting. I'll add that if you are getting even low hum or other noises, IME it's always a good idea to start at the pins. I've had tubes where the pins look ok, but after giving them a good cleaning, the noise disappears. Getting rid of a transparent layer does indeed help.

Thanks, I'll remember that. - never gave it a thought!