[GreenKeys] Crystal Filters: voice channel multiplex?

[Roy Morgan]

For the phone company among us:

I have a few crystal filters marked:

31EA, 31EB, 31EC, 31ED
and:
31EAT, - EAU, - EAW
Dated 1957, '58. and '63
Bulova Watch Company

They are in aluminum cylinders, 3/4" by 2-3/4". have four solder pins,  
an indexing nub and central threaded mounting point.

I wonder if these are meant for frequency multiplexed voice band long  
line use.

Roy


Roy Morgan
k1lky at earthlink.net
K1LKY Since 1958 - Keep 'em Glowing!