Kenwood TS-830S modifications, and comments.

Kenwood TS-830S

By Matt Erickson KK5DR

A technical article including modifications and common repairs, as well as commentary.

There are several good web sites devoted to the Kenwood TS-830S, as well as several articles which I have used myself. This article is my experiences with the radio.

The current unit I own is the 4^th of these fine radios I have possessed over the years.

I my opinion, the TS-830S, is the best transceiver Kenwood ever has or ever will make. It is one of the most reliable of any that Kenwood has made. There were thousands of them built, and a large number are still in service today.

The 830, is a double-conversion super-heterodyne receiver, but there is a third conversion level that is only active when the Noise Blanker function is engaged. However, this conversion is not a traditional type of stage, as you normally would think. The 830 is what is known as a “hybrid” transceiver, having solid state circuits except for the RF PA section. There is a single 12BY7A tube, which drives a pair of 6146B final tubes. All of these tubes are tetrodes operating in class AB1 neutralized mode. RF power output ranges from 80 to 120 watts out depending on the band and load.

No radio is perfect! Even though the 830 is very good, it does have certain shortcomings that are unique to it. Common problems to this model can be fixed with a little work.

Band-switch problems:

Mostly the shaft couplers and poor or corroded switch contacts are very common problems in the 830. Lubricate the bearings and bushings on each shaft, as well as the detent balls found in the PA portion of the band-switch. Use Pro-Gold® contact cleaner and conditioner on all the switch contacts, working the switch with each application of the fluid. A broken or slipping coupler can be repaired with the application of thread-locking fluid to the slipping shaft, or Super-glue®. If none of these repairs are acceptable, a very small screw-type hose clamp could be slipping over the exterior of the coupler, and tightened until the coupler holds the shaft tight, or any combination of these fixes can be used. I favor the use of thread-locker, and the hose clamp, since this fix can be reversed by removing the clamp, then heating the shaft near the coupler to get the thread-locker to release.

Intermittent operations in various sections:

Most of these problems can be traced to loose or corroded connections, or poor grounding of circuit boards. I fixed these problems by the application of Pro-Gold® to all of the jack plug connectors. Then I backed each screw out and retightened them to reseat all the boards. On older versions of the 830, star-washers should be placed under each screw then retightened. In later versions Kenwood used nylon filled brass board standoffs, which don’t need the star-washers, just retightening. There are few relays in the unit, but these could also become intermittent, so apply Pro-Gold® to these too.

Excessive white-noise, along with peak signal distortions on receive:

This problem is due to the type of diodes used in various sections of the receiver, as well as noise from other sections of the radio. The diodes in the product-detector are of poor quality, and can generate lots of white noise. I used 1N6263 Schottky-barrier diodes for this modification. These diodes should be carefully matched by junction resistance and junction capacitance. Remove the “El-cheapo” 1N60 diodes from the product-detector and install the new ones. The carrier level must be reset after the installation. This is easy to do with the service manual, and an oscilloscope that has a voltage calibrated display. You might ask if this mod is worth the effort, I was able to measure an improvement of about a 40% reduction in noise levels in the receiver. I notice the receiver has a smoother, less harsh sound and reproduction of the signal after the modification. The lowering of the steady background hiss reduces listening fatigue. The picture below shows a set of these diodes installed. Diodes D-20 to 23 are the product detector, on the IF board.

Distortions on peak transmit signal:

This problem is nearly identical to the product-detector. The Balanced-modulator is a mirror image of the product-detector. Kenwood also used cheap noisy 1N60 diodes here. Again, I used 1N6263 diodes, and carefully matched a quad (four-piece) set, and installed them. In this circuit the carrier level must be minimized. Use the service manual and an oscilloscope, adjusting the setting for a null in the displayed waveform. Diodes D-29 to 32 are the balanced-modulator on the opposite side of the IF board.

Noisy diodes in filter switching circuits:

Kenwood selected some rather poor diodes which switch in or out the various filters on the IF board. These cheap diodes can introduce white noise, and distortions on the signal passing through them. It would have been nice to use the
Schottky-barrier diodes here too, but the DC switching currents in the circuit is too high for them, so I used 1N4148 general purpose switching diodes, which are still far better than the diodes originally installed in the circuits.

Above is a picture of the IF board, which shows the position of the optional filters as open spaces. Diodes D-6 & 7 are placed on the crystal filter, and D-12 & 13 on the ceramic filter. If optional filters are installed, the diodes for those should also be replaced. These are D8,9,14, & 15.

PA section:

I found that a seriously mismatched set of final tubes had been installed, so I replaced them with a good matched set of GE 6146B. It is required to neutralized the final section when the tubes are replaced, this procedure is outlined in the back of the operations manual. I used my SI-4031 with a selective RF power measuring function, which made the process very precise. I found a set of resistors on the PA board that had evidence of overheating.

Above is a picture of the PA board showing the overheated resistors R-2 to 5. These resistors are in the cathode line going to ground, they are 20 ohms @ ½ watt, in parallel, they have a combined resistance of 5 ohms @ 2 watts, these “float” the cathode above chassis ground. I replaced them with two wire wound resistors of 8 ohms @ 5 watts each, for 4 ohms @ 10 watts. They should not be over heating anymore.

I found out the reason for the overheated resistors after very close inspection of the underside of the board. Below is a picture of the board showing the tube socket pin connections.

Sorry about the poor quality of the photo, my camera does not focus well at this very close range. The cracks in the solder connections are pointed by the red arrows. The common cause of these cracks is due to the final tubes being removed and installed excessively, with vigorous side to side movements during this procedure. These cracks can cause lose of gird bias intermittently and the tubes will draw excessive plate current, overheating the cathode resistors, and often blowing the primary fuse. Re-solder the pin connections, and the problem should go away.

Plate choke:

I inspected the plate choke and found that RF current had heated the coils to the point where they sagged down the insulator. I measured the inductance of the choke and found it to be a weak 55mH. Wound with #30 wire, the DC resistance is far to high for my tastes. I designed a new choke using a ferrite toroid about 1” in diameter. I used #24 tinned wire with insulation. The photo below shows the new choke installed.

You can see that I coated the assembly with hot glue. On the right hand side of the ceramic post, you can see a light blue resistor. This resistor is a wire wound 10 ohm 5 watt glass encased unit. The resistor acts as a “glitch” resistor preventing excessive plate current in the event of tube “take-off”, or other high current event.

I replaced C-7 the plate DC blocking/RF coupling capacitor, which is a .001mF @ 3kV, it had been damaged. The yellow cap at the right top in the photo is C-7, I replaced it with a .002mF @ 6kV cap. I replaced C-8, due to damage, and removed L-1, which is at the base of the plate choke (L-2), the resistor I installed takes the place of L-1.

After the mods, the unit is working well, but there are more things I plan to do to the radio. I’ll write about these modifications when I finish them.

Stay tuned…