Charles Socci - Information Technology

I picked up an 80′s vintage Kenwood TS-530s on EBay. The rig was in great shape but the output power was very low. After searching on Google for information about my new radio, I found Ken, K4EAA’s *excellent* webpage on Kenwood hybrids. Ken also refurbishes Kenwood radios professionally and also sells the parts needed to do-it-yourself.

After reading Ken’s pages and shooting him a quick email I realized that I needed to replace the cathode and screen resistors in my TS-530s. Never having owned a Kenwood, and having only some limited experience digging in under the hood of a Heathkit HW-101 I was a little bit afraid. But curiosity prevailed. I was also able to download a service manual for the radio here. I could not find schematics of the 530, but I did find schematics on Ken’s site of the 830 which is similar if not identical in terms of the final board and the rectifier board, which are the two boards where we find the screen resistors and cathode resistors.

I ordered the parts from Ken which arrived in a few days, and then I set out to make my repairs.

Ken told me the cathode resistors would be on the final board, as well as two 100 ohm screen resistors. The remaining screen resistor is a 470 ohm on the rectifier board. It took me a while to figure out what was where, but it was fairly easy to identify the four 20 ohm cathode resistors and two 100 ohm screen resistors on the final board. The 470 ohm screen resistor on the rectifier board sits right in the middle and you can’t miss it.

A SAFETY note: Danger!! High Voltage!!
“Hybrid rigs such as Kenwood TS-520-820-530-830
have high voltages that can be as high as 800 volts in the power
supply and final section. These voltages can kill you!
This is actually true of any rig with tube finals. Keep this in mind
when working inside these rigs.
After these rigs are turned off, these voltages remain
in capacitors and can still harm or kill you. Most of
these rigs have bleeder resistors that are SUPPOSED to
discharge these capacitors in a short time after the
power is off. These are usually of values in the tens or
hundreds of thousand ohms and are usually placed
across the capacitor to drain it. Are these working
right in your rig? Would you bet your life on it? I
wouldn’t.
As a safety precaution, one should ALWAYS discharge
these voltages manually before touching anything in
the rig. To do this, unplug the rig and let it set for 3 or
4 minutes. If the bleeder resistors are working, this
SHOULD discharge most of the charge. Then using a
screwdriver or a good clip lead, short the
top of the plate choke, to ground. The top of the plate
choke is the place that feeds the two tube caps by way
of parasitic chokes. Discharge the top of the plate choke. The top
of the plate choke is the place that feeds the two tube
caps by way of parasitic chokes. There is enough
voltage stored up in these capacitors to create a high
enough current to stop you heart.”

I removed the top and bottom covers of the case. I disassembled the protective cage around the finals. *make sure you short the I removed the finals, making sure to note which final came from which socket. (I don’t know if this is necessary, but its probably a good idea to not mix them up and alter the adjustment of your radio). I then unscrewed the final board from the bottom and was able to pull it out just enough to remove the old resistors and replace them with the new ones. I did the same for the one resistor on the rectifier board. I then put it all back together and proceeded to enjoy my repaired rig.

See the following illustrations (you can click on any image for a large version):

1) This is the bottom of the radio after removing the case. The final board is in the upper left hand corner and the rectifier board is just to the right.

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2)Here is a closeup of the final and rectifier boards.

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3) Removing the plate caps and pulling out the 6146b finals.

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4) The final board of the Kenwood TS-530s showing the newly replaced resistors. Note the location of cathode and screen resistors.

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5) The rectifier board showing the single 470 ohm resistor.