An IC-729 mod : From original two FET mixer to a FET ring doubl balanced mixer

Ages ago I had a chance to service an FT-1000 which belonged to an American ham. I was impressed with the radio and in the course of the service I got to read the schematic and focused on the first mixer. 




I noticed the difference between it and my old IC-729 was it had parralled FETs in the mixer so instead of just two (see IC-729 mixer circuit in the photo), The FT-1000 had a total of four which accounts for its signal handling capability. On a lark, I set out and bought some FETS and thought I would try out the mod. Just before I started construction, I consulted my CQ ferrite core handbook (in Japanese) and saw a circuit for a FET double balanced mixer which promised good strong signal performance as well as gain over the standard diode ring double balanced mixers I have used before in my projects. The only additional part I had to "make" was another transformer for one port. Please see big photo. The four FETs I bought were metal cased. The mod is not too pretty to look at but it works quite well. and of course I give thanks that my rig survived the mod. HIHI

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