300B SE Hum

[billardhockey]

I am working on your standard SE 300B With DC heating and Potentiometer controlled input. It is very quiet at lower volume. As you turn it up it has a hum that gets louder and louder as you increase volume. Is this normal? It is quiet in actual use with 96db speakers. Using it with a pre amp means turning the 300b up just enough to get a good volume and using the pre for the rest of the amplification.

 

[Tjj226]

If you short the inputs to ground, and your hum level still goes up and down with volume it generally means you have an issue in your ground or wire layout.

 

[rayma]

Post a photo of the chassis, and a schematic.

 

[billardhockey]

My question: Is that normal?

 

[kevinkr]

No, it points to a problem in design or implementation.

 

[rayma]

If it's 60Hz, could be a layout problem. Post a photo of the chassis.

 

[Jazid]

My question: Is that normal?

No, I have several different implementations of 300b circuits here (by others) and none of them show this.