tube rolling first-timer

So I bought some NOS tubes to try in my preamp. It is my first piece of tubed equipment, and this is my first time switching out the tubes for something different. The pre is a Nagra PL-L. It comes with some Sovtek tubes. The tube complement is two 12AX7's and one 12AT7.

So, I've done a fair amount of reading about different tubes, and decided to start with some Telefunkens. I found a good deal on a matched pair of Telefunken smooth plate 12AX7's and a Telefunken 12AT7.

Here are my questions:

(1) when you are first learning about tube characteristics and your preferences in your system, is it best to stick with all one kind of tube and swap them all out, or should I first switch out the AX7's (leaving in the Sovtek AT7)... I'm just curious if people think there is a "right" way to go about it.

(2) Does one generally switch to all of the same brand tube, or do people tend to mix and match brands to their preference? Of course I recognize you need to use the same brand (and closely matched) tubes for the L/R channels, so I would stick with the same brand for the AX7's.

(3) Do folks have particular preferences or combinations of tubes that they have like for the Nagra PL-L and would recommend?

Thanks for your advice and recommendations.
I would always keep your pairs the same as they usually effect each channel (one tube operating in each channel's circuit)and you want the same tone or signature sound from each channel. Change out the 12AX7 to the Tele. pair you have and leave in the Sovtek pair of 12at7 and listen to see if you like the change. That is what tube rolling is about. Find another 12at7 Tele to match up with your single.

Hey Rick, thanks very much. The PL-L only takes a single 12at7. Maybe that means it's not in the signal path and is just used for for volume attenuation? So I can switch all of the tubes to the Telefunkens (the two ax7s and the one at7) or I could try just switching the pair of ax7's first, and then try all three or try just the single at7 first....

any thoughts?

Thanks again,

Sorry for not investigating the curcuit first. I would still roll the 12ax7s first and note the change. Possibly trplace the original 12ax7s back in and then change the 12a7t. This way you can hear what affect each one can have. Finally roll all and again listen at each stage for a while. Possibly use a familiar album or set of music and repeat with each change. Its fun to listen to the changes.

Thanks again Rick. Much appreciated.

usually #2... for me.

Closely matched tubes are needs for a non self biasing unit.

Be a purist or suit yourself with the tonality NOS tubes offer. 'spensive. Frustrating. time consuming. In the end, I've found it rewarding though.

Look up substitutions for your tubes. It will either open new doors for you or outright confuse you altogether.

Number one deal with tubes though, especially if you don't get a tube tester for yourself, is to get a very reliable and knowledgeable tube vendor. Andy B at Vintage Tubes has always done right by me and I highly recommend him.

My pre uses both 12AT7 & 12AX7. I use RCA on the AT side, and Amperex Bugle Boys on the AX side. tele's would also be fine by me on the AT side too.

it's all a mix however, front to back, it's all about the mix and synergy and your preffs of course in the end. you may find too that it's not always just the tubes, but the design in which this tube or that is employed.

Roll 'em Roll 'em Roll 'em Keep them doggies rollin'...

Thanks Jim. Very helpful. I am going to try some Mullards at some point. Just doing this gradually.
Given that Nagra is extremely diligent about component choice, sound, precision, why mess with it at all? I'm sure that if there were better sounding alternatives out there with commensurate reliability, Nagra would have chosen them.
Lenny -- that's a quite reasonable thought, and where I was initially. I guess from what I've seen the Sovtek tubes aren't that highly regarded, but also, to get new ones Nagra charges quite a bit (they specially select them) Then there's curiosity at play too. But I am half expecting to swap in new tubes and decide that things sounded better with the stock tubes.
I am sure that Nagra has to live with tubes that are readily available and make their best choice among them. I my opinion, 50s-70s tubes are far superior to what you can buy today.

I know my Reimyo 300B amp came with new production Westrex 300Bs that were made with the same equipment as my 1960s WE 300Bs, but in the amp the60s tubes were quite superior.

All that I can really tell you is to experiment. Telefunken 12AX7s are still sought.
Tbg is right about the current tube selection in designs. Be it whomever... amp makers gotta choose which ones are avialable now and in good supply.

otherwise they'd say which NOS ones to use and not supply tubes with their amps, right? Leaving it up to us to feret out them still strong as new, non noisey, non fonic NOS tubes to fill it out with.

But that dog just won't hunt. At all.

Again, the true key in tube substitution is the vendor and the testing equipment they have and the measures with which they test them... and how well they support waht they sell.

I'll not mention names here either in terms of those who don't support well what they sell... but that part is integral IMHO. Knowing who is as good as knowing which.

I found not much difference from the Tele to the RCA. Some for sure, but not lots. RCAs have more lower end definition and weight IMO. tele top ends are super but that's about it IMO. both their mids were similar.
Blindjim, that still does not rule out the possibility that NOS tubes might be better in the Nagra. Trying them is the only real test.
Yes certainly sseems I'm on the right track to experiment here and will do so with interest. Plenty of agreement on that score. Intersting, Jim that you prefer RCAs to Telefunken. I've got a lot of listening to do....
How's the tube rolling going?
Hi Samhar. I have settled on Mullards and RCAs as my favorites which I prefer over the stock tubes. I also have some Bugle Boys to try. The Telefunkens and Genelex were not my cup of tea.
Thanks for the response. I'll bet you'll like the BB 12AX7"s. You might also try Amperex 7025's or Mullard 7025's, just a tighter spec'd 12AX7. Which Mullards did you try, CV 4004's or 12AX7's?
Interesting on the 7025's and thanks for the recommendations. I tried RCA 5751s and thought them not as good in my system as the RCA long black plate 12AX7s. The Mullards I tried were both short plate 12AX7s from the 60s (nice) but also the long plate O-getters from the late 50s (nicer).

Between the RCAs and the Mullards (12AX7s) the RCAs are a bit more balanced and dynamic, but the Mullards have a wonderful midrange that is really enticing. I am using the Mullard 12AX7s and RCA black plate 12AT7 -- seemed to be the best combo, although it started to get pretty subtle in trying the different combinations. The 12AT7 tube (single) does not seem to have as much affect on the sound, although I did not check this very scientifically.