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RE: Tube TC

Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>

John or Dan or ?, I have 4 833a's with original Johnson Sockets and have
wondered if way down the road they could be made to Push Pull. I haven't
studied Tubes since 74. Can you elaborate on the Culpits vrs. The Armstrong
oscillators. One thing I was reading stated that 2 Triodes in parallel cause
Capacitance problems but there were work arounds? Any Ideas?

They are not in my theory or family of curves text books.

I net:

"Colpitts oscillators are somewhat similar to the shunt fed Hartley circuit
except the Colpitts oscillator, instead of having a tapped inductor,
utilises two series capacitors in its LC circuit. With the Colpitts
oscillator the connection between these two capacitors is used as the centre
tap for the circuit.

Regards,
Jim Mora
Ojai Ca.


-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Wednesday, October 12, 2005 8:16 PM
To: tesla@xxxxxxxxxx
Subject: 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