VFO-35

                                                                                               HF-35 VFO

                                                     I decided to build a companion VFO for my HF-35 transmitter; crystal operation was fun
                                                                      for awhile but being able to move all over the band is very desireable.  This unit employs
                                                                      a 12AU7 oscillator-buffer followed by a 6AU6 buffer-amplifier.  A built-in power  supply
                                                                      with a pair of VR tubes takes the load off the HF-35 transmitter's power transformer.

                                                                      The basic circuit is from QST May, 1963, and is the VFO designed by ARRL staff for
                                                                      the "Novice Gallon MK II".  Instead of oscillators on 160M and 40M, I built this VFO
                                                                      to operate on 80 and 40.  Some might question the  layout with tubes located so close
                                                                      to L/C components; however, the oscillator  settles down nicely after about 15 minutes
                                                                      with total drift about 550 hz and no change after about 45 minutes.  Output is about 2V
                                                                      P-P, which is more than enough to drive the 6CL6 stage in the transmitter. The unit
                                                                      is stable and provides a crystal-quality note.

                                                                     The key to building a good VFO is to use very low regulated voltage on the oscillator,
                                                                     silver mica caps throughout, and lots of mechanical bracing.  In this VFO, the main
                                                                     variable is mounted on a piece of 1/8" aluminum bolted to the chassis.  The front panel
                                                                     is braced with angle brackets, and the assembly holding the band set capacitors is braced
                                                                     with a large standoff.

                                                                     After calibration, I marked the points on a blank scale with Letraset, scanned this scale
                                                                     and lettered it in Photoshop.  I then printed the final copy on white card stock.
 
 

                                    
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