TS-520 puts out half power what it used to. Replaced tubes and caps. No joy.

Discussion in '"Boat Anchor" & Classic Equipment' started by KB5JCX, Feb 2, 2017.

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  1. KA9JLM

    KA9JLM Ham Member QRZ Page

    That may be true, But replacing the tubes should not change the peaking of the coils.

    The diddle stick is not the magic fix all.
  2. W5RKL

    W5RKL Ham Member QRZ Page

    Measure the final tube screen voltage at the "SG" terminal on the Final Unit board. It should be approximately +258VDC in standby dropping to a lower
    DC voltage in TX depending on the current level flowing in the final tubes. The actual DC voltage may vary somewhat based on your home's wall outlet
    AC voltage. My wall outlet AC voltage is 118VAC +/- 1 or 2VAC.

    Hot Roding a TS-520 series transmitter typically is done by CB operator who are trying to increase power output. This is done by increasing the 520's
    final amplifier screen voltage (not a good idea). The CBer typically moves the wire from the TS-520's Rectifier Unit "210A" terminal to the Rectifier
    Unit "300A" terminal. This not only increases the final amplifier screen voltage but also the driver tube screen voltage as both stages receive their
    screen voltage from the same Rectifier Unit 210A supply.

    Look closely at the 520's Rectifier Unit "210A" terminal. If the wire is missing from the 210A terminal then it has been moved to the "300A" terminal.
    There are two "210" terminals. One is "210" which connects to the power transformer "230" terminal and the other is the "210A" terminal which has
    a wire connecting to C16A located under the VOX and Marker Unit board top left rear.

    You need to spend time studying the TS-520 service manual which you can download from my website


    Once the page comes up, scroll down to the Kenwood listing and download the service manual for your model of TS-520 (there are "3 TS-520 models).
    If you don't know what mode of 520 you have simply look on the front panel below the VFO knob, there you will find the actual model of 520 you have.

    Trace the wiring on your 520's Rectifier Unit. If there has been a change in the Rectifier U nit's 210A wiring then you will see it.

    Make sure all power is removed from the 520 and the filter caps have been allowed to discharge to zero before start any troubleshooting your 520.

    One more thing. If you change the driver tube, you do NOT have to neutralize the final amplifier!! You also do NOT have to realign the receiver

    You should also check the final tube cathode resistor, there are 2 10 ohm 1 watt resistor in parallel. Measure the 6146 cathode resistor, pin 1 to ground, which
    should be very close to 5 ohms. If the cathode resistance is higher than 5.7 ohms, replace both cathode resistors. The cathode resistor are there for the IP meter
    circuit. The voltage drop across the cathode resistor in parallel, is applied to the IP meter circuit to display "current" on the "top scale" of the meter. The IP
    meter circuit is actually a "DC Volt meter" that displays the voltage as current on the top scale. The IP meter circuit relies on the cathode resistors to be within 5 ohms tolerance.
    As the cathode resistor increase in value the IP meter indications will change resulting in errors in IP meter indications.

    Mike W5RKL
    KB5JCX and KA9JLM like this.
  3. G3YRO

    G3YRO Ham Member QRZ Page

    Not the Oscillator coils . . .

    But changing them very definitely DOES require re-alignment of the RF circuits ! (as every valve has different internal capacitance)

    Roger G3YRO
    KB5JCX likes this.
  4. KB5JCX

    KB5JCX Ham Member QRZ Page

    That's what I thought. Anyway, needing them or not, I finally got all the coils aligned including the driver coils. I now have decent output on each band, except 10 meters, where I only have 10 Watts to the antenna, but that could have been consumed by the antenna matching device. Anyway, I have to use 28.5 MHz for the neutralization process, but my SR-550 is not picking-up the signal. I am thinking of building an RF probe and using my analog multimeter set on DC as a "window" or "meter" to use for lowest reading of the SG off power - should only be about 1/4 watt output so, I built a 1 watt, 50 ohm "dummy load" for the SG off measurement so I can measure between ground and output. That should be the similar "meter" of a received signal on a receiver's meter. Any comments on that? ( I cannot believe its been a year doing this.)
    Last edited: Oct 14, 2017
  5. KB5JCX

    KB5JCX Ham Member QRZ Page

    I did change the resisters and capacitors on those items. It did make a difference, but not on ten meters. BTW-I finally got ten watts out of ten meters and sixty or more (96W on 75m) on the others. Its RF meter time now. Gotta neutralize the 6146B's.
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    I thought the Oscillator was a RF circuit. It is just a stage further back before the output driver.

    Am I mistaken ? I get what you are saying, Just playing. ;)
    That is cool, Nice work. Was that radio ever on 11 meters ?
    Last edited: Oct 14, 2017
    KB5JCX likes this.
  7. KB5JCX

    KB5JCX Ham Member QRZ Page

    I got the radio shortly after I got my license back in about 1987. It worked fine then on ten meters and I did not make any mods to it, so I am fairly certain it never was on 11 meters.
  8. W5RKL

    W5RKL Ham Member QRZ Page

    If you operated only SSB on 10 meters, never attempted to operate on the low end of 10, then you may not have known whether your TS-520 has been hacked by a CB hacker.

    It's easy to check. Simply connect a frequency counter to the RF Unit's "TP3" terminal. Page 18 in the TS-520S service manual shows the location of TP3 on the RF Unit board. If you do not have
    the TS-520S service manual, you can download it from my website.


    Set the Band switch to the following 3 ten meter settings, one at a time, and the HET OSC crystal frequency, if no changes were made by a CB hacker, will display the 3 ten meter crystal frequencies listed

    28.0 the HET OSC crystal frequency at TP3 is 36.895Mhz
    28.5 the HET OSC crystal frequency at TP3 is 37.395Mhz
    29.0 the HET OSC crystal frequency at TP3 is 37.995Mhz

    If for example on the other hand, placing the band switch to say the 28.0 setting and your counter displays "36.695Mhz" or a frequency less than 36.895Mhz, then your TS-520 has been hacked by a CB
    hacker so it operate on a frequency range from 27.5Mhz to 28.0Mhz or a non-ham 10 meter frequency. The HET OSC frequency listed above are for 10 meters ONLY. There are other HET OSC crystals
    for 160, 80, 40, 20 and 15 meters that will be less than the lowest 10 meter "28.0" band switch setting. 160 meters was only available on the TS-520S and TS-520SE. The first TS-520 did not have 160

    Mike W5RKL
    KB5JCX likes this.
  9. KB5JCX

    KB5JCX Ham Member QRZ Page

    I do not have a TS-520S or SE - I have a TS-529 and not the upgrade for the DG-5. This DG-5 must have been added at the factory because it looks like no attachment I have seen on other radios pictured called a TS-520 with DG-5 added. Regardless, the DG-5 does not work - I figure its the old story of bad grounds - but before I check that out, I have to have an operable radio that is neutralized. Again, as I said before, 10 meters (and all the others bands) worked properly in 1987. I have logs to reflect that. And the DG-5 that used to work back then (same one) confirmed the frequencies. The QSO cards I received from the contact stations confirmed those frequencies "on-the-dot." And no, I do not have 1.8 meter band on this radio, nor did it ever have it. BTW, the TP oscillating frequencies for 28.5 are not the same as listed on your site for the TS-520. Both the Operator's Manual for the TS-520 and the Service Manual for the TS-520S tune the coils on 10 meters to 28.8 Mhz, just FYI.
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    I have never seen a TS-529. That must have been a special production run.
    KB5JCX likes this.

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