Changed Tubes in AMPEG J12R

A couple of days ago I finally changed the tubes in my little 15W Ampeg Jet12R, a 1997 reissue of the classic '60s combo.
I bought it used last May and, despite some crackling and humming noises at extremely high volume ( when gigging on stage) and some farting bass notes due to the stock Ampeg speaker it worked fine, I was particularly enamoured of the tone this little monster produces, so I hesitated changing the old tubes even if I knew sooner or later they had to go.

Last week when practicing at home I noticed the hissing noise was more constant at medium volume ,so I decided to change the tubes and after some researching I bought a pair of JJ Tesla 12ax7 and a pair of matched JJ Tesla El 84. The stock tubes were Sovteks , and when reasearching for the new tubes whenever I read reviews or comparisons the Sovteks were always refferred to as a poor product, flat sounding, cardboard tone,robust and cheap but nothing more, even if they're always stock tubes on Fenders, Mesa Boogie and other name brands.
After changing tubes I immediately noticed the amp quieted down: all the noises almost disappeared , no more background hummings rattling or hissings, this shows that the old tubes were probably well used and responsible of the noise issues.
Then I discovered a new improved sensibility in the EQ control knobs of the amp, now really very useful.
At first I didn't particularly like the changed tone these tubes produce :it's a bit harsher than before, it rocks and definitely has more gain and volume, more overtones ( this I like) and less clean headroom than before, now it begins to distort around volume 5.5 with Lollar P90s or Humbuckers. With Telecaster or Rickenbacker around 6.5.. It was kind of strange to get used to this tone , because the Sovteks actually had a very mellow, warm tone that I really loved, and the distortion was darker and more profund , thay had less gain but sounded more in control, anyway I liked the amp clean or crunched with natural distortion, it's a single channel amp and I manage to get distortion out of some good pedals.
When I plugged in through the pedalboard things were better and I started to apppreciate the best definition and versatility of the JJs, they react very well to minimum changes of pedals settings and with some compression thay are not that harsh as they sound when directly plugged. Still the warm tone of the Sovteks is what made me love this amp till last week.
I've decided to keep the JJs in for some weeks, play some gigs to see how they cut through the mix when played live, then decide if it's the case of changing just the first preamp tube ,the one that shapes the sound, and try a new Sovtek ( despite the bad reputation I loved that sound) or some other warm sounding or less gainy tube.
I'd like to hear from the experts here, any suggestion on brands...or about a great pre amp 12Ax7 tube to go for if I should change only that one.
I'm not very inclined to invest in expensive NOS tubes that here are rare to find and extremely expensive. Mullards nowdays seem to be produced by Sovtek as well, and reviews don't rave about them ,everybody agrees that old Mullards are exceptional and new Mullards are totally different and inferior.... I read good ireviews about Tung-Sol..I don't know...
Hopefully the more I'll play these JJs the more I'll be able to appreciate them

Hi Andy: I wish I could be of some help. As far as tone goes; adding or subtracting one or more pedals between the guitar and the amp adds another layer of variables. All I can suggest is the tubes that give me the tone I want ... old, grungy, brown, meaty ... in the guitars and amp I use. To me, the question is do I want to gamble on NOS or used tubes or new ones. Since I want a softer, less gainy, darker tone, I go after old stuff. The only recommendation I have is that I've never heard anyone complain about old RCA black plates that run $35-$50/ea on eBay US. If you see something there you want, let me know, I'd be happy to buy/ship for you. Good luck. John

Thank you very much John.
I appreciate your amp expert tip.
That's what I needed:in the enormous amount of reviews and opinions one finds and reads on the Web,I needed a trusty voice of somebody who knows and understands amps and shares more or less the same taste for the good old sounds and tones
I've always read about 12AX7 RCA Black Plates as a reference tube,and after you adviced that I checked the european and USA Ebay and more or less the prices are similar ( cheaper in the USA for the exchange rate,but once you add shipping expenses and Customs duties is more or less the same price) and cheaper than what I feared,so I might look for a single RCA 12AX7 for the V1 position.
On an old TONE QUEST number I also read an expert advising JAN ( joint Army and Navy) GE 12 ax7 as a quality ,but cheaper,alternative to the RCA with very similar tone...do you have any experience with 12AX7 GEs?

About my current situation:I have to report that for the last 3 evenings I made a point of trying to play the JJs equipped Ampeg every evening for 1-2 hours coming home from work, and I 'm under the impression that the tone is getting better for my taste:could it be that after about 10 hours of use the new tubes are kind of "warming up " and "sweetening" their tone ,and maybe will continue to do that the more they work ???
I still notice a tone that is somehow not so warm as before , but it varies using different guitars of course.
Being more gainy these JJs break up a little earlier than before ,but on the plus side the amp is louder now: at 2-3 volume is really loud. Pedals tone is totally enhanced too, I'm stunned at how the Electro Harmonix Pulsar tremolo I use is sounding:clearer and kind of "expanded",a lush tone I 've never heard before with this small amp.Phazer and distortion pedals are also bigger sounding.
I also had the chance to try all my electric guitars with the new tube configuration: The Guild Blues 90 with Lollars ,Les Paul, Telecaster ,Danelectro and Rickenbacker 360 sound superb. The good news is that the Guild T100D now sounds rather GOOD ,less boxy ,very warm distorted tone and with feedback more in control .Before the tube change the T100D ( my favourite and the one I prefer to play live since I got it) didn't match my AMPEG very much,sounding sterile, a bit cardboard like and flat ( while with my Fender amp it's really a killer guitar).
Rickenbacker 620 and Guild CE100D have a decent-good tone,the Guild hotter and rather alluring when distorted.
The Gretsch 6119 with single coils ( with very low output) it's nothing special ,weak and colorless unless aided by the pedals.

Anyway if I happen to see a bargain on an RCA 12AX7 I'll surely get it and I'm sure it's gonna be a small good investment tone wise,but till then I understand it's a matter of experimenting a lot with guitars and pedals ,a bit of patience,some live gigs to aquire an opinion on the field .

Hi Andy; no, don't have any experience with GE JAN 12AX7s but I think it's worth saying that if your rig doesn't mirror the test rig ... it's hard to know how much weight to give those kind of reviews. Yes; the tubes need some break-in time to find their voice ... the same way speakers do. But you're on the right track; put your money in V1 and high-grade workhorse 5963s/12AU7s in phase inverter/driver and reverb drive/recovery applications. I put JJ AX7 gold pins(?) in the GA18 I used to own; I thought they were very good; bright by my tastes but punchy and musical.