In article ,
John L Stewart wrote:
The 1000 pF cap across the oscillator will form quite an effective LP
filter.
That is essentially the idea; it is possible that the oscillator might not work
at all without this capacitor. Keep in mind that the original design, not mine,
which I posted here earlier in the year, used a 10,000 pF capacitor in that
location. There is obviously a serious compromise that must be made in the
choice of this capacitor, but that is part of engineering, it is not always
possible for every thing to be perfect when choices must be made between
conflicting goals.
100 % mod looks impossible since the driving triode cannot swing
the upper triode all the way, in particular while driving that cap.
That is probably just as well as this type of modulated oscillator will drop out
anyway at some point before 100% modulation is reached.
John, did you try this circuit? Looks like a NOGO to me. Pls get the
soldering iron warmed up!
Not yet, converting my AES phono oscillator to use the high-level series
modulation scheme is a post labor day project, although I can't promise what
oscillator topology I will try first. The choice of oscillator circuit will
probably depend on my mood as I start soldering the new circuit together. There
are at least six different variations on the same basic oscillator, and I intend
to try several until I find the one that I think works best.
--
Regards,
John Byrns
Surf my web pages at,
http://fmamradios.com/