Kenwood TS-700SP All All Mode 2 Metre rig

I bought this rig at the 2013 North East Radio Club By and Sell and the friend I bought it from said he thought all that was wrong with it was dirty function switches from not being used for many years. Bobs diagnosis turned out to be almost correct and a few well aimed squirts of contact cleaner and much rotation of function knobs restored the old rig back to its former glory. I was soon using it on a 2 Metre SSB net that runs here and one night when there was a very weak signal I found another problem. I turned the R-DX switch on expecting to boost the weak signal but instead the signal vanished. I put the radio away for perhaps three years with the intention of finding out what was wrong "when I get a "Round Tooit" !.

January 2017 I found a "Round Tooit" and down-loaded all the documentation I could find on the Internet. The R-DX switch switches in and out an RF preamp via a relay and my first thoughts were the amplifying device was faulty. Looking at the RF board I wrongly identified the pre amp device as a Dual Gate FET as it was a tiny little white blob with four leads. I should have looked at the circuit diagram first. I removed Q1 and soon discover it is a Bi-Polar transistor with two Base leads, a device intended as an Grounded Base VHF/UHF amplifier. Searching on the WEB I found the 2SC1070 is quite a common device and bought two of them from the UK just in case the one I had removed did not survive my handling or miss handling. The replies to my asking questions on forums indicated the most likely cause of the problem would be the relay and of course the Omron Type MTS used had been out of production for a long time. The photo below shows how I replaced that relay with a common 12 Volt double pole double throw PCB mount relay by extending the short leads with thin tinned copper wire, heat shrink and cambric tube. After I refitted the 2SC1070 I had removed, the the R-DX switch does what Kenwood intended and I have two 2SC1070 devices for other projects.

My intention is to install it in my mechanical workshop at the bottom of the garden connected to the J Pole I have removed from the shack to replace it with a restored 2 Metre RingO.

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Written by and Copyright, Phil. Storr © Last updated 14th January 2017