What to replace CAL ALPHA dac

Agree with Buconero. Hard to beat in your budget unless you are prepared to have a SS DAC. The type of tubes you use in this unit can produce a wide range of tonal response. If you like 'warm' try some JJ ECC 83's. Since there are only 2 of them, splurge on the 'gold pin' edition. FWIW, if you are up to ss sound the Marantz 8004 is not only very good it is also a CDP and has input from other digital sources. It has gotten good reviews.

"The type of tubes you use in this unit can produce a wide range of tonal response."

The bias is set for the original tube and is not user adjustable. The original tube will usually give the most neutral sound. If my memory serves me well the Delta, in its original form, is already on the warm side. The transport makes a big difference on this one.

Rrog, What was the 'original' tube? Mine came with X brand 12AX7A's which is essentially the same tube I recommended is it not? The manual did not designate which brand of tube to use.

FWIW, while I agree with you regarding the warmth of the Delta (an ideal transport for the Alpha I think) I used a different transport for a number of years and in my system then a little added warmth was a good thing. Perhaps IF the OP is using a Delta he might not need more warmth, but I inferred from his post that he did not use a Delta.

Thanks for the responses.
I use a rotel player as a transport. And I use 5751 for the tubes, I think they're Mullards or Sylvanias.
I was hoping the current crop of DACs might sound more analog, since this Cal originated in the 90's.
I've read some positive reviews on PS nuwave, Schitt,
do they lack the warmth of the tubed Cal?

IMHO rarely does the SS equivalent of any tubed component, including DAC's, equal the latter in fluidity and, potentially, warmth. Warmth is however an additive usually depending on tube selection. Some tubed stuff is not warm at all. Usually, if you are fortunate enough to have very resolving speakers etc and are willing to pay the price you can find some SS components that can be both fluid and revealing, but rarely warmish in tone. To make the equasion more complex you must add into the mix the synergy between your DAC and transport, which as in the case of the Cal Alpha/Delta vs other transports is very important.

In your place, I would find a Delta to replace your transport before I would just buy a new DAC in your budget, especially if warmth of tone is a big priority. Actually, I would do neither, I would buy the Marantz I mentioned. I have its big brother in my system along with another tubed CDP and it is, in many respects, better than the tubed unit, and I easily live with it (but the tubed unit is still connected and is used for 'relaxed' listening sessions). Don't discount the value of having a transport matched by the manufacturer in the same unit. It can make a huge difference. The principle reason I believe for the current promotion of DAC's is the demand for something that can use other imputs by folks who no longer rely so much, if at all, on CD's for sources.

So while your Alpha can be improved in resolution etc, it is IMHO unlikely to be found in your budget range without some serious compromises you may not be able to accept.