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Sunday, January 27, 2013

A Filter for The Mighty Midget's Mate


The story of my 80/40 meter three tube (all 6U8) superhet receiver is recounted here:  http://www.gadgeteer.us/erart.htm

I've been playing with this RX on and off for many years now.  Somewhere along the line I picked up a 455 kHz filter for it (I couldn't find the 455 kc crystals that Lew McCoy used).  Yesterday I finally got around to putting the filter into the receiver.

There is almost no info on this filter on the internet.  Here are the details"
Toyo Communications Equipment Company Ltd.  CM FILTER
Type: 455 -- 2.4 -- C     Date:  8- 69

On the bottom, there are four terminals.  They are marked "P" "B" "E" and "G".   Does anyone know what these letters signify?  

 I experimented and it seemed like putting a 455 kc signal into P and B, and taking the output from E was the way to go.   I've left G floating. It works, and the improved selectivity is very evident.   But I'm operating with no specs on the filter, so I may have it in there upside down and backwards. And of course, I am operating with my usual disregard for impedance matching issues.

Here's how I've placed it in the circuit: 


Ideas, suggestions and even admonitions would be appreciated.

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2 comments:

  1. B = B+, P = plate of the mixer tube, E = earth and G - grid of the first IF tube.

    Good luck and 73, Gerard

    ReplyDelete
  2. This filter was used in the Racal RT 422 B, I am told. Schematic linked from my junkbox http://www.retro.co.za/zs1ke/junkbox/

    ReplyDelete

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