Found this info over on a JVM forum. the 11th post down here http://jvmforum.com/phpBB3/viewtopic.php?f=21&t=4409
Here is important information I´ve got from New Sensor in reply to my latest inquiry:
"The Electro-Harmonix 12AX7EH has a spiral filament and should not be used in cathode follower circuits. The Tung-Sol 12AX7, Mullard 12AX7, and Sovtek 12AX7LPS also have spiral filaments."
That would explain reported failures in V3.
The guy from New Sensor recommends Sovtek 12AX7 WA and WB:
"The most rugged 12AX7 types for cathode follower service are the Sovtek 12AX7WA and WB."
I will give the Svetlana a chance and eventually report its failure, incremental noise or any other symptom.