Title       : FTDX560 Mods
de DA2JP @ DB0MWS

Hello fellow hams.  A few of these venerable rigs are still around, so here are all the mods.  Enjoy.
Yaesu FTDX-560 Mods

A good number of these rigs are still around, so here are a few good mods.

Caution:  Proceed with the following mods at your own risk!
          Take all of the usual precautions, i.e. discharge any large            caps, disconnect the rig from power, disconnect antenna, etc

HV Power Supply Regulation

Parallel filter capacitors C601 and C602 (80uF at 450V) with two 250uF at 450V electrolytics.  This increase the HV regulation by 6-7 percent.  This will also prove avantageous with the next modification.  It should also be mentioned that if your shack is wired for 220VAC (Stateside power is 120 VAC), then by all means strap the tranformer in the rig accordingly and use it:  The rig draws close to 1000 watts after modification.

Power Output Increase

After looking up the specs for the 6KD6 final tubes in this rig, it is readily appearant that these tubes are not used to their full potential. Remove the +150 volt line from the screen grids of the 6DK6 final tubes. Fashion a bracket from some small aluminum angle stock and mount two OB2 on the bracket.  Install the new bracket on the back of the cabinet between the power transformer and the RF cage.  Install in series between the OB2 regulators and the 300 VDC source a 3K 25 Watt potentiometer.  Adjust the screen grid voltage to a value of 210 VDC.  Optionally, you may substitute a fixed value resistor once the value to obtain 210 VDC is known.  Also change resistor R513 from a 4.7K 1 watt to a 1K 2 watt.  This will bring the bias control in range so the proper static current may be obtained at about 1/4 rotation of the potentiometer.  Good linearity is found at a static current value of about 40 mA.  Before these modifications, the maximum power obtained into a 50 ohm dummy load was about 270 watts.  After the modifications, the power level obtained was 390 watts, or an increase of 28 percent.  There are no signs of "red plating" on the finals, but needless to say it is not recommended to run RTTY at this power level!

Speech Amplifier 

As it came from the factory, this rig did not have very good transmit audio.
Remove R259 47K and replace it with a 1 meg 1/2 watt resistor.  Insert a 0.01 uF cap between R266 and the mike jack.  Next, remove R2109 (470K 1/2 watt) between pins 1 and 6 of the speech amplifier (V209 12AX7).  Remove R256 and R261 (100K) and replace with 22K 1/2 watt.  C260 was omitted on later production models, but the PC board was still drilled and marked for it. Install a 50uF 15V electrolytic in this spot.  TX audio will sound much better than in the original configuration.

10 and 15 Meters

Although the receiver has fairly good sensitivity, the 10 and 15 meter bands are somewhat lacking in this respect, which was not at all uncommon for rigs of this era.  A good switchable preamp will liven up performance on these bands and still retain good strong signal handling capability on the low bands.

Well, that's it.  Good luck and see you (rather, hear you) on the bands.

  Vy 73 es cul de Jim, DA2JP/N6ZQZ


DOWNLOADED AND REALIGNED FROM THE PACKET NETWORK BY BOB G0LBQ - N6XDI.