hum on BC30 in ClassA

[tinisa]

Hi all,

 

just played on my new BC30 for the first time, and... I get an aweful hum noise when I switch to ClassA (15W), even when I unplug my guitar and when I turn off all potential 50Hz sources (light bulbs, washing machine etc...)

 

Any idea where this comes from ? Could it be from the amp itself ?

 

any help would be welcome !!!!

 

Tinisa

[wiggy]

I know this is probably a stupid question but you're not mistaking the noise from the fan with a hum from the amp itself?

[jefrs]

Mine hums too but it is a slight mains hum and common to both 15W and 30W and both channels.

 

However if I have anything else earthing on the input shield, I get a massive earth loop hum. This the only amp that does this, it is so bad I cannot bi-amp with it. I conclude that it is being caused by the BC30. I am wondering about the wisdom of a fan motor on the heater circuit.

 

If anyone has a solution to this, please post.

[MikeRom]

Mine used to hum like mad too but after changing the output tubes, cleaning all the tube sockets, opening her up and making sure everything is tight, components not touching anything, wires free and clear, cleaning the pots and checking for bad solder joints (didn't find any) it's stopped. I don't which if any of those things did the trick. Still hisses a bit tho -

[jefrs]

Been there done that, changed all the valves bar the reverbs. The 5AR4 makes a big difference. Bright caps C3 C4 C5 C6 lifted. Tidied the wiring. Single star earth. I don't like the mains connections on the board but stuck with that for now. It's own mains hum is acceptable. Hissing cleared up after the 5AR4 and more so after squirting the pots and the standby switch. Still cannot explain the earth induction loop when I tie in another amp. I may re-earth the input to the chassis. Something is wobbling the ground up and down.