Preamp tubes in power amps

I’m a tube rolling proponent , so I would say yes to both questions, but how much improvement you would hear or what brand of tubes would sound best to you, I can’t say.

If you go to tube dealer Brent Jessee’s website:

BRENT JESSEE RECORDING HOMEPAGE (audiotubes.com)

He has broad, general descriptions of the sound of various tubes. The only problem is that they may not sound that way in your gear, in your system.

You can call any of the people I mention and they will talk to you about what tubes you might like, and I have read many posts saying that all three have given the callers excellent advice.

Maybe people with the same components as you will chime in, but I also suggest calling the maker of the gear for advice. NOS tubes have gotten expensive, like everything else, so it’s hard to tell you to experiment till you find what you like.

Two other knowledgeable sources of tube advice are:

Andy Bouwman at Vintage Tube Services - Great to talk to, has great tubes, good prices, but can be slow. Many people love Andy.

Kevin Deal at Upscale Audio - Very knowledgeable but has a very no-nonsense style that some people don’t like. See the thread: Upscale Audio and Primaluna | Audiogon Discussion Forum for opinions and a couple of posts by the man himself.

Good Luck and Enjoy!

Thanks!  I’ve dealt with Kevin at Upscale.  They sold me a bunch of 7DJ8s that they promised were fine substitutes for 6922s but my BAT destroyed them, and Victor at BAT said he had no idea why someone would represent 7DJ8s as suitable.  I know the voltage is close.  But the BAT does not have a reputation as a tube destroyer,

what I’m asking is where would upgraded preamp tubes have the most impact?

Better 6922 for the preamp, but remember that the manufacturer designed your unit with modern sounding tubes in mind so you want something better in that direction meaning linear sounding tubes.
Believing that your pre has Sovteks or EH I would go with Siemens Halske E88CC and Cca up to 1967 production, for a classic tube tone, or their bigger brother E188CC same period, for more bass and treble. But definitely i would try to find some Voskhods 6N23p 74-79 production for their better flow and the info retrieval at a much lower cost.
Of course you can try anything from that family and you can get better results from the ones you already have as long your pre does not push them too much in which case your choices are limited.
A good move is the check with BAT if that is the case before spending your cash.
For the power amp I would check to put the best I could afford in the cathode follower position leaving everything else as is.
A new world.