Marc, is your board the original one that Kevin organized or the group buy that Tran did (not the more recent failed group buy) (or your own board but made from the original version)? From what I could tell, there were a few fixes that were incorporated in the Tran group buy that made it more stable out of the gate. Haven't tried Amperex 6dj8 but do recall someone saying it sent some of their transistors to an early grave (I recall they were bugle boys) - I have only used JAN Philips 6dj8 from the 80s and some german-made siemens from the 50s or 60s, all without issue.