Model Twelve drivers
An interesting tale Roy.
I had a pair of Twelves and loved them but did not have room for them so I sold them to a neighbor. After about a year he emailed me to say that one woofer and one tweeter were dead.
Short story: I sent the dead woofer to Bill LeGall who worked his wizardry and restored it to like new!
Longer version: The MicroStatics were a bonus. I used a set with my Twelves but they are not original. They're worth over $100/pr now so factor that in when you compute your losses.
The contour boxes OTOH are absolutely essential--they are the crossovers. I rebuilt not only my own external crossovers (contour boxes) but also did some for other folks. In all I rebuilt about a dozen of those boxes, using everything from NPEs to big Clarity Caps. You really need to replace the caps. Some of them are the infamous black and red PVC caps and they fail. Best bet IMHO is to use film caps for the lower values and NPEs for the higher values. A rather long thread here describes a couple of the rebuilds
http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=4111
Also replace the resistors! The Twelve used 5w resistors and I have seen more than one burned and/or cracked resistor in Twelves and Fives.
Looking at the crossover can be a bit confusing if you're trying to determine what caps are needed because there are several dual-value caps in there. Here's what is needed for each speaker:
2) 50uF
1) 16uF
3) 4uF
1) 3uF
The woofer: It's 12" according to KLH literature but as audiojones pointed out the frame really measures a bit under 11". But to avoid confusion let's agree to call it the KLH 12" woofer. The attached KLH ad calls the woofer 12" and it calls the two 4 -1/2" mids 3". Go figure.
It's true that the Five and Twenty-Three also used a 12" woofer and I, like most of us, had always assumed they were the same as the Twelve. THEY ARE NOT THE SAME. Before sending the original woofer to Bill I was looking for replacements and discovered that the Twelve's woofer has a much bigger magnet than the Five or Twenty-Three
http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=8073
Roy, your use of Twenty-Three woofers should probably be considered a temporary fix. Sometimes (rarely) Twelve woofs come up for sale on ebay (there was a pair last week for $99 that did not sell).
It may be worthwhile to send the dead one to Millersound for resurrection. Besides, the Twenty-Threes could be the perfect speakers for your apartment. Some KLH lovers like the Twenty-Threes best.
And as Glenn mentioned, the sealer for cloth surrounds that AK member RoyC concocted for Vintage_AR can make a big improvement in bass response. I was blown away by the improvement after treating the woofers in my KLH Model Fives. KLH issued a Service Bulletin back in the day that specified that all cloth surround woofers as well as the "12.5" mid (used in the Models Twelve and Five) should be re-coated. Also coat the dustcaps on the woofers.
Kent