CAL Alpha DAC: Stock vs. 24/96 upgrade

I have an integrated CDP from norh which is a clone of the CAL Delta - Alpha (w/ upgrade) in one box. It used to be made (already discontinued) by the same Thai manufacturer that CAL used to outsource the Delta-Alpha.

I've had this player since Y2000 and have done mods on it (replaced the cheap opamps) plus tube rolled. I tried these tubes - Telefunken 12AX7 (both ribbed and smooth plate), Svetlana 12ax7 (supposed to be very similar to the Mullard CV4004), GE 1960s 5751 3Mica Black Plates, Sylvania 1950s Gold Brand 5751 Grey Plates, Sylvania 1950s Gold Brand 5751 Black Plates. The Black Plates Sylvania gave the best balance and most textured presentation. Mids are just to die for. 2nd place is the GE 3mica black plate, which I believe is cheaper and easier to source. All the 12aX7s I tried are way below these two in performance.

Either the Sylvania or GE tube brings this player up a level in performance. If you wish to go another level or two replace the opamps with decent ones. I've done these many years ago and recall using OPA627s and OPA2111. My tech told me the original opamps were really el cheapo crappy variety.

Noelpastor, Thanks for your input.
Kevin

There are three CAL DACs in our house right now. A beloved Alpha (non-24/96)in the bedroom system; a Sigma II (non-24/96) in the TV room, doing great things hanging off a DVD player; and a 24/96 Sigma II that is in a cupboard gathering dust. The regular Sigma II sounds more musical to these ears, regardless of which system I A-B them in--fuller, warmer. I don't know if this experience is mirrored in the Alpha realm because I've never heard a 24/96 Alpha, but I can say that the Alpha is very tube sensitive (more so than the Sigma II) and you can get a lot out of it, as others have observed here, by putting in favorable tubes. Telefunken 12ax7s and Mullards CV2004's didn't do it for me--too flabby--and they had me wondering if I had made a mistake in buying the darned thing. Thankfully, I get experimenting. I agree that the Sylvania 5751 blackplates make this unit sing. Raytheon 5751 blackplates are really good in it too, and can be found for less $.

The following webpage contains a chart that will tell you what to expect from some popular 12AX7 varients (https://www.tubeworld.com/12ax7.htm). I don't like the Btitish coloration of the Mullard CV4004 personally. My favorite was the Telefunken ribbed plate(NOS) in the Alpha and Sigma. I owned both for a number of years to go with my Delta. I'd also suggest tube rolling and trying a cable like the the Kimber Orchid before the upgrade. If you do get an Orchid: be certain to get one of at least 1m. For some reason the shorter lengths don't get it(personal experience). (http://www.kimber.com/Products/DigitalCables/Orchid/Orchid.aspx)

Hello Kevin, Goto The Tube Store, The heading "Tube Type" on the main page, click "12AX7". Scroll down in alphabetical order till you get to
"M" There you will see this Tube under "Mullard 12AX7", it of course is not a "real" vintage Mullard, but the New Sensor Clone made in Russia.

Great Tube, I really like them in my Alpha, and as I said previously, won't break the bank, and will hopefully stop your search, and desire for futher money being spent on your Alpha. Mark