Any Vintage tube Gurus around? ID this?

[LeadedEL84]

I recently got my hands on some NOS and used vintage tubes. I usually buy modern tubes such as Electro Harmonix,JJ/Tesla,or Tung Sol reissues to replace the Groove tube/Sovteks that my amps have come with. A friend of mine has been trying to get me to try vintage tubes for years. He uses only the finest NOS tubes for his vintage amps and high end modern production tubes in his modern Marshall. I am happy with my current combination of Tung Sol 12ax7s and EH EL84s in my USA Crate V30. No reason to change.
-However-
I have been working on a Crate V5 practice amp project that I upgraded to a 10" celestion speaker and have planned to try some tube swapping experiments for fun and in search of better tone. My plan was to try a 12AT7preamp tube to lower gain,increase clean headroom,and hopefully get rid of the garbled distortion my V5 has at volumes above the halfway mark. ( more on these results later ) I discovered that the modern production tubes (in the brands I usually buy )want a few bucks more for the 12AT7 versions than their 12AX7s. While 12ax7s and power tubes of the popular vintage brands are pricey I discovered there are deals to be had on vintage 12at7s. So I bought a couple lots of vintage tubes. I over bought knowing I could try some different brands,find out what I like,and put a few back for future use. Then turn the rest around to get a few bucks back. This also helped me get a better price per tube of course. All the tubes are tested (with results provided ) and guaranteed.Some are NOS some used. Here is a list of what I have: 12AT7s-1 GE,3 Sylvania,3 RCA w/grey plate,1 RCA black plate,1 Tung Sol,1 Phillips,1 Magnavox,1 unidentified with writing worn/wiped. 12AX7s-1 Silvertone, 1 HP,1 Sylvania. EL84s-2 RCA (matched set).

I immediatly put the RCA black plate,Tung Sol,and RCA EL84s aside as keepers. Then I looked at the rest and tried to decide what to try first in my V5. The next thing was to test the others to verify they work(I have no tube tester). Also want to witness the different sound and characteristics. I realize some on the list will be better for an amp and some better for radio/audio use. I decided to try the Magnavox first.
Question: Who made this tube? I know that some of these tubes like the Silvertone and Magnavox are manufactured by someone(such as RCA or GE) and relabeled. The writing on this Magnavox tube is worn but looking closely I can see "magnavox"and some numbers:512-239-JBT
Meter readings for this double triode tube is as follows:
#1 Tested...............72/68
Tested on Heathkit tube tester

I decided to try this tube first out of curiousity and I had to start somewhere. It has been in the V5 for two days. It sounds great and I'm in no hurry to swap it out.
The first thing I noticed was a great low volume clean tone that reminds me of a vintage Fender type tone. Warm and good highs. It stayed clean even at half volume. 2/3rds volume put it at the point of break up.Pick soft for clean/pick hard for overdrive. I was expecting a little volume loss from the reduced gain but in reality this amp sounds louder now. It has more useable volume now. It used to get garbled sounding overdrive at anything above 1/2 volume. Now it stays clean and clear much longer. When I turned it to 3/4s volume I got this great vintage sounding overdrive. It reminds me of Creedence Clearwater Revival type overdrive from the late 60s/early 70s. A little EQ and volume adjustment on the guitar and pulling the EQ back to 12 o'clock on the amp gave me good blues tone with my Les Paul.
Then I plugged in the Marshall Guv'Nor pedal and played at low and moderate volumes. The tone I got after doing this is what is keeping me from swapping this tube out to try the others just yet. I can't believe the harmonics and touch sensitivity of this combination. There is so much there than before the swap. I have been playing this the last two nights and can't put it down. I am finding sounds that I never thought this cheap china Crate would ever get. It has so much detail and character. It is almost 3 D sounding. I am just floored.
So who made this old Magnavox tube? I didn't think a preamp tube would make THAT much difference in sound. I always thought the power tube made the big difference in sound where the preamp made the difference in the feel and reaction to picking and gain. I still have the stock Sovtek EL84 in there. Can't wait to try one of these vintage RCAs. ????