Stock Crack Loud Buzz/Hum Left Channel
- Thread starter Troycnc
- Start date
Carefully measure the voltage at A3.
Can you post a photo of the top side of the amp that captures the glowing bits of the 12AU7?
Alright, how about some fresh build photos?
OV at A2 and A3 with 55V at A1 makes me moderately suspicious that pins A3 and A2 are touching each other, which would short them together, then you'd get the 55V on A1 because of this.
This should be visible from photos, and you could measure DC resistance between ground (terminal 3 or 12) and A2, then ground and A3.
OV at A2 and A3 with 55V at A1 makes me moderately suspicious that pins A3 and A2 are touching each other, which would short them together, then you'd get the 55V on A1 because of this.
This should be visible from photos, and you could measure DC resistance between ground (terminal 3 or 12) and A2, then ground and A3.
Yikes, OK, so a few more tests to really narrow things down.Troycnc said:
1. Pull the 12AU7, then recheck these resistance measurements.
2. Turn up the volume control all the way, then recheck these resistance measurements.
Troycnc said:
The prior resistance measurements needed to also be done with the power off.Troycnc said:
Is there any difference in the resistance at A3 with the volume control all the way up vs. all the way down?
With the 12AU7 pulled out, you can easily measure the DC resistance between pins 2 and 3 on the tube itself.
You either have debris in your tube socket (quite likely), or you have a grid to cathode short on the 12AU7 (much less likely).
You either have debris in your tube socket (quite likely), or you have a grid to cathode short on the 12AU7 (much less likely).
I would bet on debris in the tube socket. I'd plug it back in and fire the amp back up, then recheck your voltages again.
Recheck the voltages at A3 and A2.
-PB
-PB
Those would be accompanied most likely by yet another new voltage on terminal 5.Troycnc said:
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