Hi Stephen,

I just want to find a very very quiet replacement.

Try some NOS JAN Sylvania 6198W, which should neither
be too hard to find, nor be overly expensive. I recently
got a pair via (german) Ebay for less than 10 Euros
w/o shipping. These are the quietest and least microphonic
12AU7 family members I have in my drawer - way better/quieter
than for example current production JJ/Tesla and Svetlana
ones. And even cheaper than current production samples ...

I have some NOS JRC RCA 5814A, too, which are also very
quiet, but one out of four is way more microphonic than
the other three ones. The JAN Sylvania 6198W samples are
still quieter.

If you don't mind costs, hunt for legendary TFK ECC802S,
but I can't tell from personal experience how good these
actually are. At least the specs as layed down for the
whole TFK ECC80x family were extremely rigid.

Serpentine

--
A gleekzorp without a tornpee is like
a quap without a fertsneet (sort of).