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Re: Tube TC



Original poster: FutureT@xxxxxxx

In a message dated 10/12/05 8:14:26 PM Eastern Daylight Time, tesla@xxxxxxxxxx writes:


All:

I have been looking at different VTTC's, and noticed that most all of
them are variations of the Armstrong tuned grid oscillator. Nowhere
is it explained the merits of using such an oscillator. Why isn't the
Colpitts, for example, used? what is the advantage? or drawback? has
anyone built a VTTC that is wired differently?

It would seem to me that a colpitts oscillator would give you a tuned
primary; since the DRSSTC coil works so much better on account of
having the primary tank tuned, wouldn't a tuned primary benefit a VTTC also?

By the way, I just bought a 833a tube on ebay, and plan on building a
coil around it.

Dan


Dan,

The traditional modified armstrong VTTC's also use a tuned primary.
A number of folks have built Hartley VTTC's but I never saw any actual
efficiency advantage over the armstrong despite theoretical advantages.
I believe oscillation instabilities of the armstrong may actually be an advantage
but I'm not sure.


The 833A is a good tube for a VTTC and can give 21" sparks
or so without staccaco (pulsed) operation.  Longer sparks can
be obtained with staccato operation of course with suitable
decreases in tank impedance.

John