Am 15.07.2015 15:00, schrieb Andy Talbot:
Assume you've tried putting an R||C in the source to bias the
BF245 back a bit and still ensure oscillation?
Yes, probably during you wrote that mail i have tried exactly this.
But it rises the lower voltage on the Drain and 4013, so there is a
risk that the oscillator will not work properly.
Or run off a lower voltage. Try a 74HC4013 instead of
an HEF4013 and run that off 3.3V as well as the FET; may work.
Hm in my search i did not find a 74HC4013.
What i've done then is adding a R||C between + and L. Ah and i watched
the Vgs, i.e. the input signal for the 4013. The voltage was clipped at
nearly 6V although the supply voltage is just 5V! So it was clear: The
input of the 4013 became conductive and clipped the oscillation of the
drain.
For the R i took a pot and turned so that the xtal starts to oscillate
savely (even tested with ice spray). Also some load C helped to start
the oscillation more savely. De-soldered the pot, measured it's value:
Just 1k exactly :-)
Now the LO consumes 0.9 mA! :-) And the Vgs looks much better,
closer to a rectangle. Connected to the mixers, the stereo RX - in it's
current state - consumes 5,6 mA, i.e. 28 mW :-)
73, Stefan
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