[Collins] Colpitts oscillator

[ma.locksmith at juno.com]

Oh, come on.....  everyone KNOWS that the smarter people are on the Heath
reflector!   :o)

But, I guess there's smart ones on every reflector....

While you said the mounting screws did have washers under the heads, you
didn't say whether the end of the screws protruded through the "body" of
the variable.  You also called them the "right" ones.  Can you say that
with absolute certainty?

I would assume that it's significantly more "off" at the highest range?



Ed
K1ZOK

On Wed, 1 Sep 2004 12:42:37 -0400 "Richard Keller" <rkeller at ij.net>
writes:
> I have an oscillator circuit for an RF generator with an output which 
> is
> low in frequency but all attempts to tweak it have failed. It uses 
> a
> Colpitts shunt fed oscillator using several switchable coils in 
> parallel
> with a ganged 400pf air variable cap, comprising the tank circuit. 
> The cap
> is arranged wiith both rotors to ground and stators which are 
> capacitively
> coupled to the grid and plate of the oscillator tube.
> 
> The rear section of the variable is shunted with a 12pf variable 
> trimmer
> cap for alignment of the dial. The trimmer cap at minimum 
> capacitance is
> still not enough to align the dial (32 khz low at 5 mhz) so I 
> removed it.
> Obviously the oscillator is the victim of too much capacitance. I 
> cannot
> track down the excess capacitance. There must be a theoretical fix I 
> am
> missing. Is it as simple as adding a capacitor in series with the 
> ganged
> variable; if so, what value should I start with and should it be in 
> the
> front or rear of the tuning cap, keeping in mind the "Q" and 
> circulating
> current (sustained oscillation) of the tank?
> 
> I bring my technical dilemma to this group of willing, knowledgeable 
> people
> as an alternative to the other Collins group who have dictated that 
> no
> message maybe posted which does not directly apply Collins 
> equipment. That
> is a sad scenario because there is such a great wealth of fine,
> intelligent, experienced individuals who could be so valuable to the 
> ham
> community.
> Thanks and 73, Dick KF4NS
> St. Petersburg, FL 33714 USA
> Keep the glow!
> 
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> 
> 

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