The frequency does change in real life. I am working with the design
limits of late 1950's technology. The radio in question uses an OA2
for a shunt regulator. I thought of replacing it with a high voltage
zener, but they can't handle 15mA of shunt current. They also
probably have even worse regulating properties than the venerable OA2
Argon discharge tube. A friend of mind sites the miller effect as
being the reason for f_o shift. I will have to read up to see if this
is indeed the case.
Regards,
Chris KQ6UP
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On Mon, Dec 23, 2013 at 1:08 PM, John Woodgate <jmw@...> wrote:
In message
<CANnsUMFQLY+eCBVz8ow+K+HLOREL12FBwcBXhgVO-DuQqOAfzQ@...>,
dated Mon, 23 Dec 2013, Chris Maness <chris@...> writes:
. I was trying to see how changing voltage changes the resonant
frequency.
It ought not to in real life, of course. If it does, it's due to some
second or third order effect in the tube, such as a change in effective
inter-electrode capacitance. Your tube had 4 or 5 electrodes, too,
whereas the JFET has only 3 (or you could say just 2, because drain and
source are interchangeable).
I guess spice doesn't model that though. Changing B+ has no effect on
freq in spice
The same sort of effect on capacitances might occur in a JFET, and the
model might or might not include that. If it includes it, then LTspice
will, of course, take it into account. BUT the effect would probably be
much smaller that for a tube, so the frequency shift would be
correspondingly smaller.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Nondum ex silvis sumus
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
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