Royd RR3 Replacement Drive Units
As I understand it, Revelation bass drivers are somewhat unique, either being modified (from what I don't know - does anyone have an idea?), or custom made. The tweeters, though, are Vifa units. Having dismantled one, I can't see it being modified in any way ( although Joe did modify other tweeters he used).
The original tweeter is this: Vifa D26NC - 15 - 06. It is a 6 ohm unit, and also has the following numbers on it: 27022002 (probably manufacturing date - 27 feb, 2002).
There is a very useful page here, explaining how to understand the Vifa codes. It seems that the '15' element of the code is a customer code, so the manufacturer 'customised' the tweeter for clients. The only thing that seems to change is the face-plate.
I have been in touch with the manufacturer (Vifa has been bought by Scanspeak), who directed me to their main distributor. There I was told there are no D26NC-15-06 left now.
Some research has revealed that this particular tweeter was replaced by another variant, the D26NC - 55 - 06.
This tweeter has slightly different specification, but appears to be an improved version of the Revelation tweeter, release a little later. Look at the two PDF data sheets, here:
It seems every electrical and mechanical measurement is identical between the two tweeters. More interestingly, look at the freq plots. The later tweeter (DN26-55-06) has a slightly smoother response; the peak around 14 - 16khz is flatter.
It seems reasonable to conclude the newer Vifa is a better choice, and Royd may very well have fitted them had they been available (or cheaper?) at the time the Revelation series was designed.
Sadly, the Vifa D26-55-06 is also out of production now. After Vifa stopped making it in house, it was produced under license in China, as far as I can tell. It had the exact same specifications, and one assumes Vifa kept tight quality control over their design.
There are a number (78, as of today) of new, Chinese manufactured Vifa D26NC-55-06 available from Solen, in Canada. I bought a pair myself, and they arrived at reasonable cost (just under £50GBP).
I have compared them with the very last D26-15-06 from the factory (I bought that as well - sorry!), and they seem identical so far. I shall measure them again shortly, they have been running for several weeks now.
One last thing - a slight hitch: The circular heatsink of the Chinese made D26-55-06 is slightly larger that the square one of the in-house Vifa units. The inner hole, behind the faceplate rebate, on the RR3 cabinet is slightly too small to insert the D26-55-06. I enlarged mine carefully with a sharp Stanley knife, carving away the corners. Also, the faceplate is a little tight, but can be 'persuaded' to fit without surgery. All is now well, and I have brand new tweeters in my RR3.