Altis Reference DAC problem and Repair

Dear Goners:

I like to seek your advice and help on my Altis Reference DAC model with 2 tubes. Although I had already replaced the 2 tubes in the DAC, after 1 hour continuous playing (I connect my TLO transport or another CD player to the DAC ),  the volume starts to fade and becomes  completely inaudible despite turning preamp volume high. (This is not the transport or preamp problem because I had connected  CD player to the preamp or TLO to another CD player  and there is no problem with the volume). After I turn off the Altis for 24 hours and when  I turned on the system again, the volume  comes back but again within an hour, the volume would fade away and repeatedly do so each time I tested it.  I hope you can help on the following:

1.     What do you think is the problem? And what can be done?

2.     From reading past Audiogon Forum, the creator of the DAC as well as Jerry Ozment who could repair this DAC had all passed away. Do you know of anyone familiar with this DAC and can repair/recondition this DAC?

3.     Is there a way or anyone who has a schematic and user manual I can purchase? I would really appreciate any information to  contact me at msschow@hotmail.com

Thank you very much.

Moses189