I worked in campus radio at USC (So. Carolina) in the early 70s and got spoiled by the sound of the JBL 4310 Studio Monitors. After school, in 1976 I bought my first JBLs - a set of L36 Decades (still have them and love 'em).
After finding the heritage site last year I decided to upgrade my system and started looking for a set of L300s (or even L200s) I could upgrade, but the eBay prices quickly went beyond what I could justify for a set of speakers.
Mid February I saw a set of "JBL 4505" speakers on eBay. I checked the site and with some helpful folks here I found they were actually 4320 Control Monitors - a 2 way system for recording studios from the early 70s. http://www.lansingheritage.org/html/.../1972-4320.htm
They were big boxes and required local pickup ... so after a brief delay for a snowy weekend, we drove to Philly and brought them back to Virginia.
I found a pair of 2405 drivers with diaphrams to install, again, on ebay, so they were bought and delivered a week later. I'm not a sound engineer, but I do have a technical background and know how to solder. I'm sure they weren't JBL diaphrams, but I could install the furnished diaphrams and if they didn't work right, I could have JBL techs put factory diaphrams in later.
I did a search here and found detailed directions on replacing diaphrams -
Anyway - here are a few pictures showing the stages of rebuilding the drivers, cleaning the gap with a piece of clear plastic (cut from the diaphram packaging)
and the final image with dated stickers on the back.
Once they were done I mounted them in the predrilled holes to the left of the horn outlet on the baffleboard, but I once I have the crossover sorted out I'd like to mount them above the horn.
I followed a tip from Zilch and built a pair of 3106 crossovers to tie to the high output of the exisiting crossovers in the box, but I had almost no output on the 2405 slots - tho they worked fine when substituted for some tweeters in another speaker system in the guest room.
I have minimal test gear these days - so I checked some crossovers for sale on ebay and found a pair for JBL L166 - the low cross was at 1000hz - the high cross at 6500 is lower than the 10k I'd like to use, but it allowed me to have all the drivers working until I can redo or replace the MF and HF legs of the crossover.