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From the OriginalHammondLeslieFaq
Some people feel that nothing but a fresh 40 Watt stock amplifier, a stock Jensen woofer, and a JensenV-21 horn driver, will deliver the sound. Unfortunately, the stock drivers are no longer available new. Don't fret though, there are some good alternatives.
If you just gotta have a stock woofer, then you ought to have no trouble obtaining a reconed P15 or C15 Jensen.
A stock V-21 treble driver is another matter however. These are notoriously fragile and since they haven't been manufactured in quite a while, finding a good one is going to be difficult. One thing that is said to approximate the stock driver pretty well is to use the driver currently being sold in new Leslies. This sixteen ohm driver, rated at sixty Watts, is made by Atlas and is slightly brighter than the stock V-21. Its use requires either a new spindle plate or a simple modification to the existing spindle plate. The addition of a 15 ohm non-inductive 10 Watt resistor, wired across the Atlas driver's leads, is said to make them sound quite similar to the Jensen V-21.
If you want to consider non-stock treble drivers, the Atlas model PD-60 and University Sound model EV1829, are said to be good sixteen-ohm replacements. The compression drivers that are normally used to replace the stock unit have a 1-inch throat diameter, with either a threaded or bolt-on mount. These will require an adaptor to allow their use with the treble horn assembly.
Regarding treble drivers, the highest frequency produced by the Hammond is around 6 kHz. Treble drivers used for PA use typically produce usable power to 15 kHz and beyond. Treble drivers with exceptional high-frequency response are probably not required to reproduce an adequate amount of key click and may be un-desirable in this regard. It's really a matter of personal taste.
Ruby apparently makes (or, at least, made) a replacement diaphragm for the V-21 driver.
It's Ruby part number 
RRDJ16,
and vibroworld.com used to sell it.
This information was posted on the TheHammondForum by JeanMarcMuller, who adds:
The new part fitted exactly to the V21 Jensen driver of my 122 Leslie. The wiring leads have the same angle as the original one and I could solder it directly to the connections on the black bakelite piece. All I had to do was to punch 2 additionnals screw holes into the border of the diaphragm with a belt punching plier. It was easy to reassemble the driver and to center the coil. Now the driver is working very fine, without distortion or any buzz. It's realy a second life for this older Jensen driver and I'm happy to keep a vintage driver in my Leslie.
However, ScottHawthorn says~:
I have it on good authority that they suck.
I have a friend - (this is info only - I make no profit from this), Dave Phipps at Opti-Case/Opti-Sound in Henderson, Texas who manufactures a direct replacement to original specs for the V21 driver. The phone is (800) 637-6635. I have not heard one of the units - but Dave is a Hammond long time Hammond man and has done my road case work for years. He is a top sound man, as well and does work for many top groups in the rock & country field. Last June I was in his shop and he introduced the line of drivers to me -- he has them in stock (at that time). Don't know the cost. I think he just does the diaphrams - don't know if complete driver replacements are available. Call him for info.
Hammond-Suzuki currently uses a 100 watt ferro-fluid cooled driver in their new-production Leslies. These are reported to be fairly bulletproof, and to sound very good. (H-S: 514-140491 ?).
(They won't mount directly onto older spindle plates though. Either you need to drill new holes in yours, or buy one of the new model (H-S: 560-137804) plates.)
Another alternative: SalAzz make a driver mounting plate which will mount any 1 3/8" x 18 threaded driver into most Leslie models (using the old style spindle plate.)
James Skinner makes adapter plates to mount an Atlas PD-60 directly onto a stock Leslie. I own one, and it is very well made. You can usually find his stuff on ebay.
One thing about the Atlas drivers is that they are very large. There's a large plastic "bubble" on the bottom that you can remove to make it much closer to the size of the original Jensen. Unless you bought a PD-60 with an optional transformer, the bubble is completely empty. Even if not, the transformer is bypassed for 16 ohm operation and you can remove it.
TonewheelGeneralHospital has begun rebuilding buzzy/blown Jensen V-21 drivers. Failed drivers can be shipped in for repair, exchanged for rebuilt units, or rebuilt units can be purchased outright. Rebuilt drivers have new diaphragms and mounting gaskets installed; as far as I know we are the only shop that has new gaskets - these are very important for positioning the voice coil within the gap. The original gaskets have been compressed during their decades of use and do not work satisfactorily with the new diaphragms. For information see http://www.tonewheelgeneral.com.
DavenportsMusik in Sweden sells used V-21´s that they have removed from cabinets wich were sent in for restoration. They replace them with heavy duty horns instead so they sell out the V-21's for about 150-200€ per unit. These are second hand units and as they say should not be used to replace a driver blown by heavy useage. -- kuremyr @ corpusmail com
I made really good experience by using a hifi-midrange dome driver as replacement for the jensen V21. In my case I used the Visaton DMR 120 which is a 2" dome driver. Since it's a 8Ohm device you have to add a serial 8 Ohm 20W resistance to get appropriate impedance matching. This resistance won'nt affect the sound in a noticeable way. Single restiction is the somewhat lower sound pressure of the dome tweeter - but if you can live with it - my 145 sounds great again. Harald-
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TopicRepair, TopicModification
Monacor KU-516
I replaced my Jensen V21 by a Monacor KU-516.It's a 16 Ohm speaker. I made a adapter plate from wood. See my video on youtube: http://www.youtube.com/watch?v=BSjnl1ECMHc . The Monacor sounds very good and it is a simple and cheap solution for replacing the Jensen driver.
Gr. ALbert
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