Nice work by Art Dudley on the Advent restoration this month. It seems that I am probably the world's expert on them. This happened by accident when I restored my parent's old speakers and got a bit carried away when I went to document the Large Advent. There were more variations than I thought and I therefore wanted to know about all the differences:
Just a few notes, those are *very* early tweeters that I believe are rare and a bit fragile. The much more common later revision had tinsel lead in wires that were visible, and a mesh metal grille. If the rear input plate is metal then the box is also very early.
The woofers have been replaced with the much later round magnet Jensen version. This version has a paper dust cap as can be seen in the photos. The masonite type is the correct woofer version. A thread covering the different woofers that I've come across:
My older brother pointed out years ago that they did not sound right in the midrange being very bright and forward. We were building our own speakers by this time and I was exploring transmission line bass loading so I was not to worried about it since they were not my speakers.
I tried adding line level baffle step compensation (BSC) when I restored my parents pair and this seemed to cure the boxy (papery) sound in the bass-midbass, and the bright character. I am highly impressed by their sound with BSC. There are a few comments here about it; this fellow likes the LA with BSC better than his Celestion SL6si's (post #97):
Here is part of my collection:
There is a loaner BSC line level box if Art is interested in trying it.
There is a discussion concerning grille cloth here:
Advent used a very coarse weave (16 ct) that looks a bit more like burlap than anything. Sources are given in that thread but I was unable to find it back when I redid a pair so I used 28ct Irish Linen that looks excellent. I would not go finer than 28ct and the original is probably better.
Advent capacitor replacement: