Questions about RCA 5751tubes

3. There is a reason the Sylvania's are higher I would imagine. They sound beter but that can be subjective? I had some RCA black plates and liked them ok but preferred GE black plates. I am talking about triple mica.

1. JRC is just the military designation for RCA. Tyey are IMHO just as good if not better than the white letter RCA branded tubes. These are not like getting a JAN Phillips tube instead of an RCA.
2, They are close enough values I find to call it a match. The difference that you would note if any is a difference in volume from one channel. The number refers to filament draw and is a better estimate of the life left in a tube than a striaght gain or Mu reading. I don't know it as well as I should. My testers are Hickoks and use GM. The Filament is what causes the tube to boil off electron from the anode to the cathode. If it is shot, the tube is virtually useless.Typical NOS is given as 1.9 but is dependent on whose testing and which tester thyey didn't callibrate.
Sylvania which may come as JHS if triple Mica Blackplates are considered by most a better tube than the RCA or GE. The Sylvania is hard to find and is a full tone tube with good extension and a sweet mid. I also like them the most. I have a pair in my rig now.
The mystique surrounding the GE grey plates that have been hawked here is myterious indeed they have the least defined and least refined sound of any even 2 mica RCA blacks like the Commands.
The green red tips are a dealer's grading scheme. It is not mlitary standard and can mean anything. Red is the Top grade in some dealer schemes.
The poor print is par for a 5751 which are uncommon as NOS.
The tube you ordered is exactly what you got.
If anything the military name like VT-231 for a 6SN7 is preferred. White print was used on the 50s tubes so you have a preferred tube early vs later when red was employed.
The Sound you have to judge for yourself. I think it is just less of the same overall presentation the Sylvania provides. Typically a littlle leaner but very clean.
If you can scare up a few bucks try the JAN 70s and 80s , get some grey plates beg for Sylvania triple mica blackplates and for Raytheons windmill getter a very popular tube that is also very very clean. Both will likely cost you about $150/pair in good shape today.
The GE triple mica (JG if military) blackplate the premium consumer brand was called 5 star at one point. Sylvanias Gold Brand frequently a 2 Mica grey plate with Blatty bass didn't always come with gold pins the 3 mica gold brand blackplate was always steel pin. All are tubes to try as well.
I can tell you a sampler LIke that will cost you a ton of money and took me a couple of years to assemble.
It takes time to find decent used or NOS- ish tubes. Even dealers pass on some pretty lousy stuff.
Also don't forget the current production. It has a very distinctly 5751 upper end. I think only Sovtek is making it now. Don't recall Shuguang ever doing it.
Finally there are a few Amperex and supposedly Telefunken 5751s . I warn you to avoid European as the 5751 is a truly USA tube and while there is sufficient belief that Amperex did maake them, I own a pair, they look like GE to me. Telefunken????
The only thing I misseed was the silver clip. It means something to one dealer in particular but is common to all 3 major players GE RCA SYl. Finally really there is one other true American brand that is not terribly distinguished for the 5751 that is Tung Sol. Somewhat harder to find but usually not expensive because they are so so. Some dealers will ask money for rarity but demand was low when I bought. figure a $50 tube in ANOS condition.
I am tired if you want more write to me via agon. And remember I am only one jackass amongst the many, we are mostly opinions.

I would also have recommended the GE black plates as the best 5751. However, the RCA JRC is a very sought after NOS 5751 made in the 50's - 60's and was also made as a grey plate version. Vacuum Tube Valley sells the RCA grey plates for $100 per tube, so price wise you did okay. The numbers are demonstrating that the tubes are closely matched, meaning they should have equal strength and current draw, which is what you want. I believe that matching is probably more essential for Power tubes. There isn't any true test that can determine how long any tube will last. These are military grade and more rugged to last longer. I have had 5751's last as long as 7,000 hours and had others die much sooner. My advice is to decide whether you feel the RCA's are equal to or better than the Sylvania's you ordered. If not, you should be able to return them without questions asked.

"Better" is purely subjective, and system dependent. The RCA w/clips may very well sound strident/overly bright in a system that already has that tendency. It does provide the best sound staging of any 5751 type though. In general- many that like 5751s, prefer the RCAs over the Sylvanias. Usually the triple micas w/o the clips however, as they are somewhat warmer(I'm a TLK ECC803S lover myself). To tell anything with regard to tube life from test results, you have to know what that particular tester's tube chart lists as "nominal new", "minimum good", etc for comparison. I seems presumptuous of a seller to send someone tubes other than what was ordered, but- that's just my opinion.