Very interesting thread.
It shows the amount of passion and time necessary when one takes the vintage speakers path. Divers, magnets, filters all degrade with time.
Restoration or replacement is difficult because very few people know how to do it correctly AND you can never know if the sound you get corresponds to the one that those speakers had 50 years ago. Some vintage Altecs have been "restored" or "upgraded" in such a way that they share very little points with the original character of the speaker.
For a newcomer like me, the Altec world seems like a jungle.
I felt completely in love with the bass of the 604 driver when I listened to an old version of Shindo 604's speakers a few weeks ago.
The mids and the treble were not to my taste, and the stereo image too, but this was certainly due to the amp used ( a modern class AB Luxman SS integrated) and to the fact that the 604 is known to be the most difficult Altec driver to use.
But the bass !!! Oh my !!!
the very first time for me that I heard a bass so uncanny, so free and fast, and super super super clean. Like if the instrument was talking and I could hear every single letter. A bass so natural that it left me completely speechless.
It also made me decide to look for a pair of vintage Altec's. The "Nineteen" may be the one the most to my taste in terms of mids and treble.
Clearly the weakness is the fact that this bass does not go very low ( seems that fast and low are just impossible to reach ). The 30cm of the Harbeth 40.1 goes much deeper but it sounds completely "in a bag", "unbreathing" and super damped compared to the Altec bass.
I read somewhere that the Altec 12' driver ( 33cm ) gives a deeper bass than the 15' ( 38cm). Is that true ?