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I think my CAL Alpha DAC is broken...

I've owned the 24/96 version for at least a dozen years. Lately, it has become very temperamental about what tubes it will accept. The left channel blows out anything other than a Sovtek 12AX7WB! I've had the following new-out-of-the-box tubes fail within the past year: Sovtek 12AX7LPS (3 of them!), TungSol ECC803 and Sovtek 12AX7LP. Typically, they last only a few hours.

I'm eventually going to take it for repair, but I'd appreciate any thoughts on:

a. why it might be doing this now?

b. why the Sovtek WB seems more robust?

Thanks.
mbailey
rodman99999
6,129 posts
 
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).
woodyandchristy
4 posts
 
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.
mike2015
2 posts
 
See here:https://forum.audiogon.com/discussions/tubes-for-cal-audio-labs-alpha-processor
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