Yes, when all is okay. Yours sound like the PSU caps are leaky and need replacement.
3 responses Add your response
Only some tube amps have an issue with no load when being turned on.
I believe the Model 5 is dc coupled, you need to monitor (with a meter) the dc offset on the amp.
It could also be the source giving dc offset into the input.
You could try to put shorting rca plugs on the input of the Model 5 to see if it's ok, if so then you may have a problem with the output stage of your pre or source.