Tubes for Herron's Preamp

I recently bought the Herron Audio's Line Preamp and finds the sound lovely. With a view to improving the performance, I am thinking of using 6922 of other brands to replace the Sovtek. Does anybody have any idea or experience as to which 6922 can do the job? Thanks.

I guess the obvious choices certainly are Mullard/Amperex/Telefunken. I have the Mullards in my Rogue 66 preamp and like their bassy warmth, if that is what you are into. Just a suggestion.
I would call Keith Herron about what he thinks of changing tubes .I also own the Herron pre-amp and he was pretty firm about leaving the tubes in the pre- amp alone. He designed the pre- amp with them and he feels they are the ones to stick with . Changing the power cord will give you better results in my opinion.
I agree with Tweety, Keith spoke to our audio society about the preamp a few years ago and said the same thing about the tubes. Felt the Sovteks were very strong tubes and worked best in his circuit.

Thanks for all the advice. In fact, I have learnt from other sources it is better to keep the original Sovtek and to buy matched ones from Herron in case of replacement. Regarding Tweety's advice, I will use the Van Dan Hul's Mainsstream AC cord to see if there is any improvement.

By the way, I am matching the Herron with a pair of Passlabs Aleph 0 monoblock and the combination works wonderful. What I am thinking of is to replace the speaker with the JMLab Micro Utopia.

Any opinion or advice is welcome.

What speakers do you have now, and what are your listening preferences, room size, etc.? The Micro Utopias and Mezzo Utopias are my favorites in that line, as they work better in more rooms because they don't have the deep bass and size of the bigger speakers, but there are a lot of choices in that price range. The electronics you have will certainly not be embarrassed by any speakers you use, that's for sure.