Electronic Specialty Products, LLC



Notice the interface circuit attached to the tube shield in the lower left side of the photo.  The twisted cable is the VFO signal cable. Also notice that the DFD-101H is powered from the gray wire connecting to the receiver dial lamp power using the red alligator clip.  THE DD-101H/U EXTERNAL DIAL CONNECTS TO THE RECEIVER THE SAME AS THE DD-101H INTERNAL UNIT.  THE DD-103 CAN ALSO BE CONNECTED THIS WAY ON MANY RECEIVERS.

Included with the Digital Dial are a VFO signal cable, power cable, and a tube shield/interface circuit assembly.  The interface assembly is used when connecting to tube receivers or other high inpedance circuits.  The assembly uses the capacitance between the tube and the tube shield to couple the VFO signal to the Digital Dial.  If you have a VFO output jack, it is low impedance and the interface assembly is not needed.

On some transceivers that have an external VFO connector, the VFO signal can be found on that connector.  The Kenwood TS-520 is an example.  It will be low impedance.

There are two easy methods for connecting to the VFO (local oscillator) of tube receivers, that don't require soldering.  Method 1 is the best if it works over the desired frequency range.  It is easy and does not pull the oscillator.  Method 2 is also easy but it does pull the oscillator a little.

Method 1)    This method only works with receivers using 7 or 9 pin miniature tubes.  Remove the tube shield from the oscillator tube if there is one, and replace it with the shield and interface circuit assembly provided with the Digital Dial.  It will work on both 7 and 9 pin tubes.  Don't push it all the way down.  It must not ground to the chassis.  Clip the BLACK wire to ground.  Now plug one end of the gray cable into the interface circuit and the other end into the VFO input jack. Turn the level control to maximum and check if the display is counting over the desired range.  If it is working over the desired range, this is the best method to use.  The RED wire is not needed with this method and can be cut off.

Method 2)    This method works on receivers using a gang tuning capacitor. Remove the interface circuit from the tube shield. There is a loop of green wire on the interface circuit board.  Cut the loop at the top.  Now twist the green wires together one half turn to form a very small capacitor (called a gimmick). Clip the RED alligator clip to the stationary plates of the oscillator  section of the bandspread tuning gang capacitor.  It is usually the section nearest the front panel.  Clip the BLACK wire on the frame of the tuning gang.  Adjust the input level control to maximum, and check if the dial is counting.  If it is not counting, or is not counting over the desired frequency range, twist the wires another half turn.  Continue this procedure one half turn at a time until the dial is counting over the desired range.  Don’t twist them more than necessary, it will load the oscillator more than necessary.  Insulate the interface board after the final adjustment so it doesn’t short to the chassis. 

NOTE:     When a connection is made to any oscillator it will have the effect of lowering, by a small amount, the maximum frequency that can be tuned on each band.  It is a problem only if a frequency that you want is at the extreme high end of the band. The problem can be corrected by realigning the high frequency trimmer for that band, with the dial connected, or tuning the frequency on the low end of the next band.


Electronic Specialty Products, LLC •  3054 Moore Drive •  Oviedo, FL 32765
Phone 407-366-4859