[HBR] 6U8 as mixer in heterodyne VFO

[Ian Wilson]

A VFO configuration that interests me for receivers and/or transmitters is
to
mix a stable low-frequency oscillator with a higher-frequency crystal
oscillator
take the difference, and filter. For example, 2.5 - 3MHz mixed with a 10MHz
xtal to get 7.0 - 7.5MHz.

I am thinking of reworking a homebrew whatsit I picked up somewhere. This
has a small PSU, pair of 6U8 triode/pentodes, xtal socket, triple variable
cap
(probably ARC-5 RX), etc.

Which of these schemes is likely to work better (or is there an even better
alternative?):

  a) pentode as mixer with both inputs to g1
     (using triode as xtal osc, other pentode as input buffer and other
triode as cathode follower o/p)

  b) pentode as mixer with one input to g1, one input to k
      (using pentode as xtal osc, triode cathode follower to mixer k, other
triode as cathode follower o/p)

I prefer to use an input buffer so that the xtal oscillator signal doesn't
get pushed back to
the input. And the cathode follower seems a good use for one of the triodes
and will allow a fairly low
impedance output.

73, ian K3IMW