Fender Bandmaster hum.

[Oddvar R]

I still have hum in the Bandmaster. I have changed all the capacitors, the filter caps, tried all different grounding locations, changed all the tubes, but still has hum, even with only one power tube installed. What could possibly be the cause of this? The only time I get a reaction in lowereing the bias. Could it be a fault in the transformer somehow? To high voltage somewhere? (I have taken away the ohm selector and I am using only two jacks, as in the Bandmaster layout.)

[sonicmojo]

You’ll definitely get hum with only one power tube installed. Have you tried a different pair of output tubes (hopefully closely matched) or do you have a bias probe to check the bias on each tube? Sounds a bit like mismatched output tubes to me but could be something else.

[Colossal]

This solder joint looks a bit dry

joint.png

[Oddvar R]

You’ll definitely get hum with only one power tube installed. Have you tried a different pair of output tubes (hopefully closely matched) or do you have a bias probe to check the bias on each tube? Sounds a bit like mismatched output tubes to me but could be something else.

I have tried all tube combinations I can think of. Nothin seems to influence the hum. Except when I pull out the v4. Very little hum.