300B amplifier loud AC noise ?

[santitrucco]

Why does my 300B amplifier make a relatively loud AC noise for the first 3 seconds after turning it on?

 

[grovergardner]

If it's using AC filaments, they will often hum until the high voltage kicks in. What is the amp? Pictures?

 

[santitrucco]

Schematic some similar. Interestage Transformer.

 

[grovergardner]

What is the power supply?

 

[as_audio]

Switch on noises are to be expected.

 

[grovergardner]

Not necessarily. I just worked on a pair of 300B monoblocks. There was no noise at switch-on. It might be normal or there might be something wrong.