OB Pad Voltage Changing Over Time

[Quiet_Storm]

I recently changed out the power supply boards on my 2A3 v1.1 Paramounts. When I rechecked all the voltages, I noticed that my OB pad voltage had increased significantly. Instead of being 151 volts like when I originally built them, they read ~180 volts. Everything else looked fine, and I went ahead and adjusted the potentiometer to set the values back to 153 volts. Is it normal for the values to change over time?

Also, I solved a multi-year issue related to some white noise on my left channel during startup! Apparently, one of the diodes had a cold solder joint, so the startup voltage on B6 was high. Once the regulator kicked in it would drop and the white noise went away. I'm not sure how I missed that before, but I'm so glad that's finally resolved.

[Paul Joppa]

No, it's not normal. It does change if you change tubes though, and it will drift over a long usage time. Check again after 100 hours or so, just in case the tube is a little flakey.

But then, sometimes things happen for which you have no explanation. If it's stable and working right you don't always have time to figure out why it was different before...