[Kenwood] TS-120S inquiry

[Dr. Gerald N. Johnson, electrical engineer]

Over the years, I've had two TS-120S. I sold the second one after buying
a TS-130S which I still have. I prefer the 130 for having filter
switching independent of mode (when desired) and WARC bands. I asked
$325 or so at a Des Moines hamfest, got $275 for the 120 about 4 years
ago.

The receiver of the 120/130 is crunchable on a good antenna with a few
strong signals. For home use, I've gone to a Tentec. The Kenwood
receiver is not horribly bad, but signals on 75 meters that splattered
in the 120 and 130 don't in the Tentec on the same antenna.

Two years I ran the 130 at a club FD on battery, with solar panel all
CW. Worked fine, made plenty of contacts with the power cranked down to
25 watts output which kept the key down current down to 7 amps or less.
It was tolerant of antenna tuning (even with full output) for maximum
output. And the 120s were also tolerant of that condition. E.g. the PA
transistors are very good or very well protected against high SWR.

The 120/130 will go into oscillation on the higher bands on occasion.
Its nearly always cured by lifting the top cover and bolting the RF
board (under the bandswitch) back to the chassis. Between mobile use
vibration and the relaxation of the plastic board material under
pressure the board loses grounds. There is a Kenwood service bulletin
about the 120 that also suggests a bias change for the PA board. I've
not detected the need for the bias change in several 120 and 130 that
I've fixed by tightening the screws, either locally or by remote
control.

The TS-120 VFO has a bit more temperature drift than the TS-130 VFO
because the temperature compensation has been changed. There's a Kenwood
service bulletin about that also. I found in one of my 120 that a few
solder connections on the VFO PCB needed solder which helped it also.
Proper temperature compensation was also a detectable improvement.

The 400 Hz filter is from Inrad, and doesn't solder in place of the
Kenwood filter because its too big. Mine is anchored to a bandswitch
support with lacing tape and wired to the IF board with miniature coax.
I find that filter begins to ring with CW above 25 or 30 WPM. Its nice
in the 130 to be able to receive CW with the SSB filter. The 120 doesn't
allow that when there is the narrow filter installed.

My 130 is NOT for sale.

73, Jerry, K0CQ

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.