Amp sound occasional momentary cut out


My Integrated Jolida Hybrid 1501RC occasionally has a momentary sound loss/cut out, no volume change just a pause on both channels.  How can I test, trouble shoot a problem like this?  I have tried different sources and inputs. 
bremner1
Thanks for the advice.  Lights stay on, so i'll check the connections.  I may also put back in some older tubes.  I put in new tubes a few months ago. I would guess if it was one tube it would be on one side only. 
Lights stay on so it is not the power cord or fuse. It would only be a power supply tube or tubes none of the others. I assume it does it with all your sources? Say turntable and CD player? A protection circuit could do that via a relay but you would probably hear a click when it happens. I have never seen a protection circuit in a tube unit. They are usually pretty hard to hurt. 
Thanks.  The amp is solid state, with two tubes in the pre circuit.  It may have a protection circuit.  I'll take a look for anything loose.  
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