arc vt150se

Have you tried switching the tubes yet[one set at a time]?Could simply be a bad tube or dirty tube socket.You can clean the sockets with Deoxit and a pipe cleaner,be sure to unplug them the night before so they can discharge.Also you can try wiggling the speaker cables and interconnects to check for a bad connection.If there is an internal part beginning to fail,these remedies of course won't work and it's time for the repair shop.Not a good idea to poke around inside,the voltage can be lethal.

>> Not a good idea to poke around inside,the voltage can be lethal. <<

High voltage will not hurt you, high amperage will drop you dead...

-RW-

What about when there is no preamp connected to it?
Will it still emit that crackling noise ?
There might be a faint hum when nothing's connected but it will be a safe thing to try