@ghasley and @facten - many thanks for the comments. I've heard a lot about EL34s and other tubes, nothing about 6dn3, understanding the role it plays in the amp explains why it's not part of the tube rolling discussion. Good to know, too, about the KT66; the Leben has switches to change the cathode resistor and plate voltage setting to accommodate different tubes, along with a chart in the owners manual regarding the tubes and settings, I just need figure out what an X, O and triangle shape mean (see here: https://www.atconsumer.es/wp-content/uploads/CS600X_Manual.pdf)
Appreciate the link to audiotubes, I do find the subjective opinions about tube sound helpful before buying.
A final new-to-tubes question: for the sockets in the Leben (I assume other amps, too) labeled for example as "EL34", would any tube indicated as EL34 work? For example, the Sophia EL34 tube is labeled as "EL34-ST" - is an EL34 the same thing as an EL34-ST or is an EL34-ST not interchangeable with an EL34?
Tube Rolling Leben CS-600X
I acquired a previously owned Leben CS-600X a couple of years ago and have really come to enjoy its sound. It's my first tube amplifier, I'm interested in exploring what more the Leben has to offer by replacing the tubes, and welcome the experiences/recommendations of others. The amp is currently running:
1 Sylvania 6DN3
4 Electo-Harmonix EL34EH
Interestingly, amp is currently running a JJ ECC802-S in both 12AU7 sockets and one of the 12BH78 socket. The remaining 12BH78 has a JAN-6189W
This article was interesting (https://jeffsplace.positive-feedback.com/tube-rolling-in-the-new-leben-cs-600x-integrated-amplifier-sophia-electric-vacuum-tubes-nos-12bh7as/) but I am not sure I want to invest in Sophia tubes when the cover will not fit back on the amp.
Feedback/recommendations on tubes welcome!