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Author Topic: Hammarlund MFA-3, 3.1KC bandpass filter made by Collins  (Read 3809 times)
WA6NEQ
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Posts: 33




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« on: September 14, 2012, 10:41:11 PM »

Will this stump the Elmers? In a box of stuff I purchased was this grey rectangular cylinder with a 9003 and a 6AK5 mounted on top. The bottom has a 7-pin tube plug. The silkscreen says "BAND-PASS FILTER 3.1KC HAMMARLUND PT. MFA-3". "MANUFACTURED FOR HAMMARLUND MFG. CO. BY COLLINS RADIO 522 9032 014". I did find a catalog online that shows that Collins made some mechanical filter adapters for some popular radios and they began with a 522 p/n. This one wasn't listed. The idea was that you removed an IF tube from its socket and plugged this adapter in place of the tube. Since the ones in the catalog look just like this, I think its a good guess that this is a mechanical filter adapter. The question is which Hammarlund receiver was this made for? Anyone know?
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KQ6Q
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Posts: 976




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« Reply #1 on: September 17, 2012, 04:23:53 PM »

The 7 pin socket on the bottom is a major clue - the 6BA6 was a very popular 7-pin IF tube. look for a hammarlund rcvr using that tube in the IF.  I homebrewed some adapters like that to modernize a National HRO Sr when I was in high school - the Collins filter and 6BA6 went under the chassis, and a Vector adapter with 11 pins on the bottom,and  a 7 pin and 9 pin socket on top had the detectors and 1st audio. There are two of the Modified HRO's there somewhere, the one I built, and the one my Elmer, the original W6VX built.  They'll also have the first three tubes after the antenna replaced - 9 and 7 pin miniatures replacing the 6D6 and 6C6 with grids on top.
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