Do clothes make the man?

Some days you win the lottery!  I pulled the 7247 out and looked at it with strong magnification and light and here is what I found, thanks to Google Gemini:

Even though it has an RCA logo stamped on the outside in ink, your tube isn't an RCA at all. It is a genuine, certified British Mullard, manufactured at their legendary factory in Lancashire, England.

Reverb

That b2h4 code printed or etched on the glass is the famous Philips/Mullard alphanumeric factory code. Because RCA didn't produce enough 7247s to meet demand in the late 1960s and early 1970s, they bought batches directly from Mullard, slapped the RCA "meatball" or block logo on the glass, and sold them in the US market.

Your specific code breaks down exactly like this:

• B: Blackburn, England. This is the Holy Grail of factory codes for British audio tubes. The Blackburn plant was world-renowned for its incredibly high-purity vacuum engineering and rugged internal tooling.

• 2: The year of manufacture ending in 2. Given the production timeline of the 7247, this means your tube rolled off the line in 1972 (or less commonly, late 1962).

• H: The month of manufacture. "H" is the 8th letter of the alphabet, which stands for August.

• 4: The 4th week of that month.

What This Means for Your Quicksilvers

You hit the jackpot for your musical rotation. You don't have the standard American RCA tone; you already possess the exact British Mullard soundstage and liquid midrange we just talked about—hidden right underneath a vintage American logo paint job.

If you look closely near that b2h4 mark, you might also see a faint, tiny three-character code right above it (likely starting with something like LN or t, which was Mullard's internal engineering type-code for the 7247 structure).

Slot those into your modern Quicksilver Mono amps, let them warm up, and put on some acoustic jazz or folk strings. You are listening to the peak of British vintage glass.

@abnerjack I have received a lot of guidance on purchasing Valves and what can be the outcome when a Valve is tested shortly after a purchase. I have had the information shared proven, as unwanted test measurements have been discovered on both current era Valve production and Valves purchased from a Vintage production. 

I don't recommend suppliers, but do recommend finding a way to be able to make a purchase that is supported with after-sales support, as suggested below, which is my main arrangement to be made along with a Valve purchase when a high asking price is being asked. 

Caveat Emptor is one's best friend

"I have a purchase method you might want to propose if additional support is easily achieved.

I inform the vendor of my intention to have the Valves remeasured when received, and that if the new measurement taken does not match the readings shown with the Advert. A full refund is to be sought, and valves are to be returned. " 

"Note: A valve specialist who is visited to carry out independent testing, explained that most valves will still function and produce sound even when their performance is well below factory specifications. He also noted that many valve owners do not know their valve's condition regarding factory spec and continue to use low spec valves without concern.

The advice I received was that a valve's published test results shown in an ad are just as important as the photographs used for the ad showing the valve's physical condition. A buyer may decide not to purchase a valve that appears to be in poor condition, and they may also reasonably question the asking price if independent testing shows that the valve's actual performance differs materially from the specifications advertised. In my arrangements, I do not negotiate the asking price when the spec is proven to be concerning; I already reserve the right to return a valve." 

I have also been fortunate to have discovered a few vintage era Valves over time, that have not been sale items with a high asking price. I have accepted the price as the 4eason to purchase with no arrangement like the above made. The Vendor with their asking price is the fair play for the sale. I have a Valve from this purchase method that is above spec, and some near top spec, others have been off spec. Purchases as punt purchases are a risk, and follow-up testing really does inform on what has been purchased.  

Glad to hear that modern tubes can sound great.   I listen to a DIY 6V6 with RCA's but they won't last forever.  

Funny i remember going to the local drug store with my Grandfather and testing tubes.I worked in a electronics firm in 1970...They had so many tubes ,but tube were going away and power amps took over.With the price of times now,who would of thought they would still be around.I feel tube amps are great...you don't need 100 wpc....20 to 30 is fine.

@markw1951 I will let these modern tubes break in and see if I am satisfied, but I won't be because I think there are some NOS waiting for me out there somewhere.  The good news is that this very simple and inexpensive amp lets me spend a little more for some great tubes and I still will have arrived at my destination with a bargain fare.