Help with Pricing of a Rebuilt Working Harman Kardon A50K Tube Amplifier

My Dad had rebuilt this HK Tube Amp. It works really well, although the power button sometimes sticks when turning it on or off. Also, it is missing the top but I think it makes it look more interesting.

Anyways, it says it is ’The Award Series A50K’ on it but I cannot find this particular model anywhere.

I am trying to figure out how to price this!!

Link to Image of Tube Amp