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Author Topic: Kenwood TS-120s vfo mod  (Read 5712 times)

Posts: 13

« on: April 27, 2013, 09:28:53 AM »

Just so that some of you are aware, if you do the vfo mod on the 120s and perhaps the 130s the mod that is floating around out there that shows removing C17 and C18 from the circuit board and modifying the ground post to install the new caps from LH to post inside the vfo can will not work 99% of the time.
What will happen is that when the vfo is reassembled, the frequency will be off by more than 7khz. What happens next is interesting, the vfo will start to drift up frequency at a rate of 5khz per hour.
This is because the inductance has increased inside the housing and the lead length of the new caps are beyond, way beyond what they should be.
Normally you would only replace C17 (12pf) and C18 (15pf),C17 being the temperature compensating cap.
I have repaired well over a dozen 120's with just replacing the aged caps and "have tried" the other mod with terrible results.
This is only for FYI, you will have to set the trimmer cap as to the reallignment specs by setting the vfo on the analoge dial to 50khz and adjusting the trimmer to bring the digital readout into line.

Glenn, VA7VO

Posts: 131

« Reply #1 on: April 27, 2013, 11:31:42 AM »

The Kenwood TS-120s / TS-130s HF rigs are from the 1980's. They were great little rigs for the time and many still in use today. I have several of each and really like them. They are very simple hf rigs compared to todays radios, but they sound really good on the air and have a good receiver assuming the radio is in top electronic conditon. They do tend to drift, but thats due to the coil / cap vfo design of the day. Most all the rigs back then that employed this type vfo design would drift some, some more than others.
Buying the Kenwood digital vfo options back then would set you back a pretty penny, but they can sometimes be found on the internet on many of the buy, sell, trade ham radio sights. I have used the Kenwood digital vfo options on  the 120 /130 / 530 / 830 rigs and it makes them rock solid.

Another option is to use this:
The K4DPK vfo stablilizer board. Check out his link below. They are reasonabley priced.
I have installed many of these vfo stablizer boards in many older model Kenwood HF rigs.
Follow the instructions for your rig.  I wire it, test it, then wrap it with some insulating material, and tuck into the rig near the vfo. It will stop that annoying drift. Works great in analog vfos in the 120 /130 / 530 / 830 / 520 / 820.
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