I think my CAL Alpha DAC is broken...

Sounds like some bad caps in the power supply.

I had my Alpha repaired by the guys at approved audio service a few years ago. CAL had long since closed there doors. Approved was the east coast service provider for CAL. The cost of my repairs were worth it to me. Funny after they opened mine up they called me and asked where I got it. It turned out to be kind of special. see the link below to my old thread on the issue. Yes I still have it but do not use it often.

http://forum.audiogon.com/cgi-bin/fr.pl?ddgtl&1158371576&openmine&zzVegasears&4&5#Vegasears

www.approvedaudioservice.com

I bought a spare LASER unit from Approved Audio when I owned my ALPHA/DELTA combo and Icon MkII. They seemed very knowledgeable and trustworthy. If I were going to have one rebuilt: I'd buy another pair of NOS Telefunken ECC803S's to pop in there(VERY transparent and extended).

I had a similar experience, i had read the supposed merits of the russian reissue tungsol 12ax7 so i bought a pair and they didn't even last four hours so i popped my trusty 1955 GE 3mica blackplates back in and felt better immediately, i find the military specific tubes superior in my 24/96 alpha, the mullard 12at7wa [wa is english designation for military as i believe wb is for russian military] pair that i have have at least 1000 hours on them with no trouble, 500-600 hrs on the 5751's - no trouble. If you do need svc. on a CAL product don't hesitate to call Approved Audio in Conneticut, fast turn around, reasonably priced, very knowledgeable about the product and has parts stock, he just repaired an Icon cdp i use in my system at the shop and it works like new.

See here:https://forum.audiogon.com/discussions/tubes-for-cal-audio-labs-alpha-processor