Re: Tube TC

["Tesla list" <tesla@xxxxxxxxxx>]

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