AN/FRR-24 bandpass filters made by Vectron

According to the 1952 AN/FRR-24 manual, the 125 cps (Z-401) and 250 cps (Z-402) filters were manufactured by Vectron Inc., 235 High St., Waltham MA
Z-401 was a crystal filter and Z-402 an LC filter. The FRR-24 was initially shipped without the crystal filter which was provided later. Unfortunately I can't read the date on the Z-401 filter box that I have.

FRR-24 filter assembly as delivered
IMG_6966.JPG (3086947 bytes)
As shown in the manual
IMG_6967.JPG (4013288 bytes)
IMG_6969.JPG (2984072 bytes) IMG_6971.JPG (2716948 bytes)
Crystal filter provided later
IMG_6964.JPG (2963071 bytes)
IMG_6965.JPG (4483924 bytes) IMG_6972.JPG (5089964 bytes) ==