Re: [TCML] VTTC-tuning. John got me started ;-)

[futuret@xxxxxxx]

Hi Bart,

By "tuning", I mean all the needed adjustments;  grid coupling,
main coupling, main tuning, grid feedback, grid resistance, tank Q,
etc.  Many of these adjustments interact.  For whatever reason,
some VTTC's are harder to adjust than others.  This can depend
on the type of vacuum tube used, and various other parameters.
The stability of the modified Armstrong type oscillator commonly
used in VTTC's is not all that stable also.  The oscillator can actually
drift back and forth and lock onto different frequencies.  The
various adjustments and parameters can affect this.  Set up
is probably easier if the various voltages and currents are monitored
with meters.  I usually don't bother.

In one VTTC I had to tune at about 10% lower frequency, but
in another I had to tune about 15% lower.  Much of this was
explained by the spark loading, but not all.  I think as the frequencies
split from over-coupling, a different tune point is needed to take
advantage of the best power point for power transfer.
Someone had mentioned some other information about this
about a year ago on this list.  I don't remember the details.
The Corum's VTTC book mentions something about this also.
(Some of their ideas are correct.)

Cheers,
John


-----Original Message-----
From: bartb <bartb@xxxxxxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Mon, 30 Mar 2009 11:33 pm
Subject: Re: [TCML] VTTC-tuning. John got me started ;-)
=0
D

Hi John F., 
 
futuret@xxxxxxx wrote: 
> But regarding tuning, the primary tank 
> often has to be considerably lower in frequency than the 
> secondary frequency, from a calculated point of view. 
Can you explain this more? 
 
I'm certain you are correct and Dr. John also stated "tricky tuning". 
I'm curious as to "why" this is necessary (from a "calculated point of 
view" if known or even from experience). 
 
Thanks, 
Bart B. 
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