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 |
As shown in the manual |
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| Crystal filter provided later |
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