The TS-850 has been my travel rig of choice for serious contesting since I used it on Howland Island in 1993. This rig has many advantages. For those who want to learn more, refer to the ARRL product review at www.arrl.org, and to the personal owner reviews at www.eham.com.
The only serious disadvantage to the 850 for an all-band operator like me is the lack of a provision for a separate receiving antenna for the low bands. There are three fairly easy ways to overcome this drawback. The first, which I used at V31DJ, is to install an external pre-amplifier, such as an Ameco PT-3 or a Palomar P-310X. These pre-amps have t/r relays built in to protect the pre-amp from a transmitted signal from a transceiver. I used the Palomar and installed a small toggle switch on the back of the unit to switch the EWE into the pre-amp instead of the transmit antenna. All I had to do was lift the wire running from the xmit/rcv relay to the band switch and connect it to the common of the dpdt switch and connect the ewe and a wire from the relay to the other poles. I also had to install an rca jack on the back of the unit for the ewe input. With this simple mod, I was able to use the relay in the pre-amp to automatically switch to the receive antenna on receive and to the transmit antenna on transmit. When the pre-amp is turned off, the transmit antenna is in-line all the time. Another alternative is to use an external coax relay from www.rfparts.com. A good one is the CX-230 for under $100. This would be switched by the rig. Finally, a simple mod to the radio is possible as discovered by WA3WJD. See http://www.mods.dk. Another mod (shown on that site) that is highly recommended is the Noise Blanker mod, which entails the removal of two capacitors. Wow, what a difference!
My previous Kenwood was a TS-830s, which I really loved. In the 1982 ARRL DX CW contest as V3MS, I was running a nice big pileup, and I felt the need to crank down the bandwidth. I vividly recall using the VBT control to the point where I could just hear a few calls in that massive pileup. I was looking forward to the same effect with the slope tuning on the TS-850, but initially I was disappointed. Initially, I just thought is was a dumb feature. Then I figured out that I was the dummy. Because I was using a 270 and a 500 Hz filter. The VBT barely worked at all. Switching out the 270 for another 500 "turned on" the slope tuning feature and it works great - just like the old VBT. I have mismatched SSB filters, but the slope still works. It's not optimal, but it works ok. Still, I'm thinking of matching those, too.
Recently, my friend V31MD experienced a receiver failure on his 850 (serial number 3xxxxxxx range). The symptom was that the receiver was deaf - absolutely no signals and a white noise background. The problem turned out to be the 6631 DDS chips on the CAR Unit board. Kenwood, recognizing a problem, has upgraded the design of these failure prone chips. I don't know the serial number of the change, but the new chips are numbered 66312 and they are stock in my 850 serial #50900145. My original 850 worked fine for many years, but failed in Belize during the storm season. It's possible the earlier chips were static prone, I really don't know. Certainly, there are many 850's with the earlier (6631) chips that have never failed. For those who can't afford a sudden failure (DXpeditioners like me!), it might be a good idea to do a bit of preventive maintenance and replace any 6631's, even though it's expensive. While it is "possible" to replace them individually, it is not advisable to do it because these chip are surface mount and have many many leads. Fortunately, a plug replaceable CAR Unit board is available from Pacific Coast Parts.
My TS-850 has been modified as follows:
Noise Blanker mod; CW sidetone volume mod; DVK volume control mod; computer and internal keyer mod. All the mods are pretty straightforward and answer most of the complaints I've ever heard about features lacking on this radio. All mods are shown at www.mods.dk. If you're not a contester, just do the noise blanker mod. It's easy.