Thanks. I actually found it here (www.head-fi.org/threads/price-drop-western-electric-421as-nos-nib.907974/#post-15063367). I read about the 421A and did a search. Luckily the seller still had one of the five available and I grabbed it.
How hard are they to find these days? And is 250 USD/EUR pretty much the expected price for an NOS specimen?
The other 4 tubes are with me