Krell KAV-3001 left-channel cut-out

While moving this amp with the power on I noticed that the left speaker cable connection was loose - after tightening the connection the left-channel of the amp went dead! For every input there is no left channel output. Diagnosed the problem by switching the speaker outputs and the right channel works fine. It's definately a problem with the left output.

I presume this is caused by a blown tube inside the amp, but as I have practically no experience with high-end amps can anybody else offer diagnosis/assistance with fixing this?

My main concern is where I can have this fixed and the cost. Does the entire unit need to be shipped to manufacturer or can a shop open this up to replace a tube?

Any help is appreciated, thanks.
Ken M.