Do clothes make the man?

@abnerjack  Wow, those are nice speakers. I'm not sure which specific model you have, but both are claimed to extend down to 25 Hz (-3 dB) and have a sensitivity of about 89 dB.

From what I've read, the 5-inch midrange driver covers an unusually wide frequency range—from about 150 Hz all the way up to around 5 kHz—because there is no electrical crossover between the midrange and tweeter (most speakers cross over between roughly 2.2 and 3 kHz). As a result, the midrange driver is likely to beam at higher frequencies, meaning its off-axis output is weaker than its on-axis output.

With that in mind, how does the soundstage from the upper module perform when driven by a low-powered tube amplifier?

At a 150 Hz crossover point, I think the REL subwoofer should integrate well with the system. However, I'd also be tempted to bi-amp the woofer section and see how much the overall system scales up, as well as how it compares with using the REL.  My theory has always been that the speaker's original woofer integrates better with the rest of the system than an external subwoofer, particularly in terms of pace, timing, and texture.

@pindac   Thanks for finding that tube.  This seems like a foolproof solution doesn't it.  I'm shopping for them now.  Any specific seller you like?

@lanx0003 This is the Verity Parsifal.  Again, it doesn't have a true woofer, only the midrange.  The specs show it to be, if I remember correctly, 91 efficient.  If the larger woofers are  out of the picture, I think it would probably be around 94-95.  I havent noticed anything negative about them.  I listen at moderately low level and near field, so I don't ask a lot of them.  I think it is a match made in heaven.  It would be hard to bi amp as I would have to tear in to it, and I don't have the desire to do so.  Thanks for the feedback.  BTW, I really like the Rep's because you can adjust them when necessary.  As you know, bass is all over the place, depending on source, so I find this an elegant solution.  It is fun too!  Sorta tailoring your own sound, like you can do with your clothes.  I love puns.

After more deep diving, I think the Mullard is the ultimate, with the GE being a better bang for the buck and the RCA a good option.  Maybe I need all three.  As Sir Walter Scott so famously said "Oh what a vicious loop we weave, when chasing what we can't achieve."  No wait, that was Google AI.  

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.