Modifications
The X-Lock generates a control voltage for tuning the VFO by means of a varicap diode. A power diode (1N4004) and several other parts are provided with the kit to build a varicap "correction" tuning circuit but I decided instead to use the existing RIT line in the TR-7. To do this I had to combine the X-Lock control voltage and the RIT voltage, I used a circuit designed by Joe KC9LAD which with only three resistors and one signal diode, does the job nicely!
The diagram in Fig.1 below shows the additional diode and resistor network together with the interconnections for the X-Lock output and the voltage from the RIT control point on the main board.
Joe also suggested that it would help with physical installation if I were to exchange the 6 electrolytic capacitors for titaniums which are much smaller for the same electrical specification. Although I did not do this, it would be a desirable modification for installations where space is at a premium.
The clearance above my chosen mounting point for the X-Lock would have prevented me from using the straight pin headers supplied with the kit and their associated plugs. After quite a bit of analysis, I determined that I could keep the plugs provided that I installed the pin headers at 90 degrees, as shown in Fig.2. By carefully bending the solder side of the pin headers down 90 degrees, the pins would still be inside the PCB mounting holes a little over half way. As the PCB has high quality plated through holes, I could solder the top side and then flow the remainder of the hole with solder from the bottom. Since there is not a lot of ongoing pressure on the pin headers, this modification should last the life of the devices. NOTE: Be sure to bend the pin header pins so that the tab for the plug is downwards (against the PCB).
The assembly sequence of the board components should be altered slightly due to the modification for the pin headers. To avoid having difficulty with other components being in the way, install and solder the modified pin headers first. Remember to solder from the top first, and then flow solder the bottom. After this, follow the instructions as supplied.
The assembled X-Lock board is mounted on the bottom of the TR-7 main board. As mentioned, more space could be made available by replacing the 6 electrolytic capacitors with tantalums, but it is not an absolute necessity. All interconnects are close and easily accessible on the bottom of the TR-7 main board.
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