Boonton 1120 and 1121 filter cards
With 5 boontons and several missing filter cards plus the need for A weighting S/N measurements did a quick layout for the filter board that can be assembled as a 400 Hz filter, and A weighted filter or as an "audio" filter per the circuits in the Boonton manual.
They were done in expressPCB. They fit the miniboard footprint (and will need a portion cut off) so $51 will get three in about three to four days.
Enjoy.
PCB Schematic Assembly lists
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Demian Martin
Product Design Services
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