Re: VTTC provisional results

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Herwig Roscher by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <herwig.roscher-at-gmx.de>
> 
> Ed Phillips wrote:
> 
> > You could play with increasing the feedback and/or reducing the
> grid bias resistor, but all that might do is just make the tube hotter.
> 
> Ed,
> 
> Been there, done that :-)   And you are right of course: It made the
> tube hotter.

	Sorry about that!

> > You could use a separate oscillator to drive the tube which drives
> the coil.  That way you could adjust the frequency and leave it
> alone while you try different coupling values and primary tuning.
> - I have thought on this as well. From a diathermy machine I
> removed a 150 W triode (together with the powersupply) which I
> could use for this purpose. The main reason I did not build this
> configuration was, that it would not be selfregulating. If the tank
> circuit changed its frequency because of thermal heating or
> introduced capacity (remember that the cap is 700 pF only), the
> oscillator frequency  would be stable, driving the tank with the
> "wrong" frequency. This would cause unwanted "side effects".
> Agree?

	Unless you are using a very temperature-sensitive tank circuit
capacitor don't think the small amount of frequency drift would be of
much significance, and you could always do a small amount of tuning if
needed.  The drift would still be there if self excited, for that
matter.

Ed

	Second thought.  That is a mighty small value of tank capacitor. 
Forget what frequency you operate at, but perhaps you need to increase
the tank capacitor substantially and at the same time reduce the
coupling to the secondary.  Your primary may have such a low loaded Q
that efficient coupling just isn't possible.