Abe, You been busy!
Interesting path your going down.
Markvetnz,
Could be the original tubes were getting alittle tired and with a fresh pair your pre came back to life.
Yep the ECC-33s in another design other then Supratek would certainly raise your eyebrows.
I also tried them in my Chenin afew years ago,HO hum.
I had one really quiet pair of TungSol black glass oval plates which I used for a short while then sold, couldnt resist the going price.
Tried Western Electric 350Bs and metal base EL-34s, better kept for an investment also tried some early 1960s CCAs in the phonostage, save your money if your thinking of buying tubes like these.
If you bought tubes like these years ago and still have them sitting in a drawer or in a closet.
Put them in a safe....