mcullinan--
I think you may be seeking the CBS-Hytron 5814wa tube, not 12Au7.
I think they are different tubes.
The 5814 is generally considered the desirable CBS-Hytron 12au7 variant to get.
Someone may correct me here.
Check Ebay. They do show up fairly regularly for about $40 a pair or so for very good used or NOS.
I use a pair in my Audio Mirror PP1 and enjoy them a lot.
If they are early 50's they may be Hytron 5814's
If they are mid fifties they are usually CBS-Hytron 5814's.
If they are late 50's they are usually labled CBS 5814.
Allegedly they all sound the same.
Allegedly the Raytheon double mica 1950's black plate is rumored to be maybe the same tube by some accounts.
I have a 1957 pair of these and I am not sure I could distinguish the two in my setup if blindfolded.
As noted-maybe a 1950's Raytheon black plate 5814 can be found easier.
Good luck.
I do believe LKdog is correct in his summary of the various designations. At least, that is what I remember when researching these several years ago.
I actually have the CBS-Hytron 5814A, not the 12au7 as I stated earlier. It has black ladder plates, double mica, D getter. Red print on glass is:
JHY 5814A
CBS - HYTRON
Made IN USA
Not 100% sure of the exact date, but apparently, mid-50's. I got my NOS pair over 5 years ago from MachMat.com for $65. Very nice sounding tube. I would describe it as rich and musical, with good tone and nice mids.
Sorry for the small and blurry pic...best I could do.
