Pentode Power Tubes - Ultralinear vs Triode

DPHP user here.

Check out the KT77 is you like the EL34 sound. To my ears they are a little more dynamic overall. Look at KT88 for more on the bottom end at the expense of less midrange magic.

 I have been using the old RCA 6l6G coke bottle in my PL. They are a lower power(different from modern 6L6). They are a close enough combination of EL34 mid and KT88 dynamics.
One of the few NOS American power tubes still available for a reasonable cost.
https://www.ebay.com/itm/RCA-6L6G-Smoked-Glass-Tube-NOS-foil-twin-D-getter-copper-grid-posts-code-35...
They have a "dry"sound which to me is more convincing compared to the "lush" EL34 tone.

I prefer the triode setting most listening sessions. A flat recording sometimes sounds better in UL. You are aware of the 2 innermost preamp gain tube also will fine tune the sound? Subtle, but another tweaky option.

Be an early adopter and try the KT170
https://primalunablog.com/2020/10/30/tung-sol-kt170/
They should be like a supercharged KT150, which already is a powerful tube. I haven't tried them in my amp yet. 8=$$$$

I use a non PL amp triode wired pushpull in class A running a quad of KT-77's and it sounds fantastic.

i would concur with others that the modern russian kt77 labelled gold lion genelax (gold and red box) is pretty much the best sounding current el34 variant

good linearity and drive with a fair dose of tubey magic 

I have a PL Dialogue integrated. Hands down the KT150 is my favorite and my change of pace the 7581A. I am a Streamer using the Roon interface. I like Ultralinear for Radio and Triode for everything else. I have heard others mention they prefer the EL34-7581A tubes with the PL HP power tube array. It’s hard for me to imagine going to any other power tubes since I seem to have found exactly the sound I’m looking for

Thanks for chiming in. Like so many other things, it seems the devil's in the details. Someday I'll know better than to think I can come up with a simple rule of thumb without more exceptions than rule.
I suppose when you start getting into tube rolling and mode of operation the changes are subtle enough that everything else has as much or more influence. I'm surprised no one has mentioned changing modes with different cables yet.

KT77 were already next on my list of tubes to try. I got the 7581A because a lot of their described attributes were also appealing to me, and they are about $100/set cheaper than the KT77. For my speakers and listening habits I definitely don't need more power and I don't feel I'm missing any punch. I keep trying things and muddling through because "You can't get what you want, till you know what you want."