Follow-Up on Packard Bell Hum Problem

[JacobsNova]

My previous thread..
http://ampgarage.com/forum/viewtopic.ph ... hlight=hum
I have done a couple of things to try and fix this hum problem. #1 I took out my input selector switch and I took out the hum balance pot so everything is original to specifications. The next thing I did I went to the geofex.com webpage and followed his tutorials on tracing down hum and the tutorial on checking the power transformer because one of the possible causes of hum is a leaky transformer. The transformer checks out okay. By the tutorial I am reading the only thing that might be the problem is that a bias supply with excessive ripple injects hum directly into the grids of the output tubes. So I did what he said and added another capacitor but the hum is still there. I'm just wondering if this is still a problem because if I ground my grids at all the output tubes pin 1 and 2 the hum goes away. I'm just wondering what I should do next. Any help is appreciated...

[M Fowler]

Do you have the cathode of V1 wired directly to the ground of the input jack, this reduces the first gain stage hum in PTP builds.

Mark

[20to20]

Your factory diagram specifies a 5U4 but the hand drawn PS shows a 5Y3 and a 300R resistor ahead of the first filter. Are you still working with a 5Y3 and the modified input components? Your 5Y3 is only good for half the current of a 5U4.

[20to20]

Any progress?

[drz400]

My previous thread..
http://ampgarage.com/forum/viewtopic.ph ... hlight=hum
I have done a couple of things to try and fix this hum problem. #1 I took out my input selector switch and I took out the hum balance pot so everything is original to specifications. The next thing I did I went to the geofex.com webpage and followed his tutorials on tracing down hum and the tutorial on checking the power transformer because one of the possible causes of hum is a leaky transformer. The transformer checks out okay. By the tutorial I am reading the only thing that might be the problem is that a bias supply with excessive ripple injects hum directly into the grids of the output tubes. So I did what he said and added another capacitor but the hum is still there. I'm just wondering if this is still a problem because if I ground my grids at all the output tubes pin 1 and 2 the hum goes away. I'm just wondering what I should do next. Any help is appreciated...

You can inject hum directly into the OT if they are not T and are too close. Since they have no end bells I would try and turn them 90 degrees to see what happens

[20to20]

My previous thread..
http://ampgarage.com/forum/viewtopic.ph ... hlight=hum
I have done a couple of things to try and fix this hum problem. #1 I took out my input selector switch and I took out the hum balance pot so everything is original to specifications. The next thing I did I went to the geofex.com webpage and followed his tutorials on tracing down hum and the tutorial on checking the power transformer because one of the possible causes of hum is a leaky transformer. The transformer checks out okay. By the tutorial I am reading the only thing that might be the problem is that a bias supply with excessive ripple injects hum directly into the grids of the output tubes. So I did what he said and added another capacitor but the hum is still there. I'm just wondering if this is still a problem because if I ground my grids at all the output tubes pin 1 and 2 the hum goes away. I'm just wondering what I should do next. Any help is appreciated...

Any Progress??