I am looking at some new output tubes to try in my latest idea. The 1626 looks good. A low mu and lower power output tube so if the amp is transformer coupled I will get a good half to three quarter of a watt. Not to much .... not to little and only $5 a piece. I have a lot of 6S4A's and 6P14P-EV's but I want a cool looking coke bottle shaped tube. I have some coke bottle shaped pentodes like the 6Y6G .... and they have the advantage that they have the same pinout as a bunch of other pentodes. But the 1626 is a true triode like the 6S4A and will likely sound better; although you never know.

But do I need to break the mold and start using a true pentode .... or atleast use a triode strapped pentode. I was thinking of the 6AR6 or 3D21WB but they would have so much power. I dont want to use these tubes and then have to barely turn them on so I dont fry my phones. Any suggestions? Dont you use 1626's Aerius?

Nope, I use 1633's, the 25V version of the 6SN7. The only pentodes I have are 12 & 6W6's, they sound quite nice in triode mode, but I haven't fiddled with them in a while and the circuits are still in the proof of concept stage. Personally I don't worry much about the power of the tubes, as long as you keep the gain down you can run them wide open in Class A with no issues.