kenwood TS-50 Power Mod for QRP
"Honey - I Shrunk the Rig"
by Bob Gobrick WA6ERB - 19-07-1998
No this is not an article about Kenwood shrinking their new TS-50 HF rig into a "CB" sized package, but the "shrinking" of the low power level on the TS-50 from 10 watts to 5 watts output in order to "officially" comply with the nationally recognized QRP power level for contest operation.
Prepare yourself before you remove any covers from the TS-50 - this is no Hallicrafters (feel a little dated) with 6L6's glowing in the inside. All components are surface mounted and to conserve space surface mounted subassemblies stand up at right angles all over the place. No place to work with that stubby tipped Weller soldering gun. But have no fear, this QRP mod is simple - you just need a screwdriver with a blade the size of a toothpick.
If you check the schematics you will see on the TX/RX board two potentiometers to set the Low 10 watt (pot VR15) and Medium 50 watt (pot VR16) power levels. The high power level is fixed at 100 watts by resistor R214. Our goal is to get to VR15 and set it for a 5 watt output.
First remove the top cover, set aside speaker and remove the latched speaker bracket (gives you better operating room). Locate two teeny-weeny pots next to IF filter module in the middle of the TX/RX board. The pot closest to the front panel is VR15 (low power adjust) and the one closest to the back of the rig is VR16 (medium power adjust) - the pots are somewhat marked on the PC board. Hook up a QRP wattmeter, dummy load and power and while in th low power mode adjust the pot (I used a flat blade calibration tool I had around) for 5 watts. That's it. You may notice that you can crank the pot all the way down to 0 watts so set where you want. I suspect the medium power adjustment with VR16 can also go to zero so maybe you can go QRPp by setting the low power pot for 999 mw and the medium power pot for 5 watt.
PS: Kenwood Service cautioned that their automatic antenna tuner requires 10 watts to actuate so this adjustment may affect that operation. You may want to check if Kenwood actuates the low power mode when the antenna Tune button is pressed. Also don't expect to run this rig off of a small solar cell for field day - the unit and all of it's surface mounted components draws a bit of power - enough for the internal fan to come on even in the QRP low power mode.