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

[bartb]

Thanks Dr. John.

That is a fantastic list of tuning issues which should come in handy for 
VTTC coilers. If the top terminal is making that much of a difference, 
then it is certainly a finicky coil (it may be quite difficult to make a 
tube coil portable). The tuning issues themselves are fascinating to me 
from an LC aspect. I've noticed this need to detune with VTTC's which is 
why I asked the question. It appears there is an inductance or 
capacitance that is in series or parallel with one of the coils (not 
related to a resistive component). Is there an LC aspect regarding the 
tube itself? I'm not a tube guy, so that question may seem silly.

Regards,
Bart

Dr. John W. Gudenas wrote:
> Hi Bart
> Here is a short list of tuning issues:
> 1) The tube impedance needs to be considered in the tank circuit
> 2) The coupling is high and the secondary height (like in any coil) 
> needs to be adjusted empirically
> 3) Good RF capacitors are essential considering both voltage and current
> 4) Tapping the primary helps, but the adjusting tank capacitance in LC 
> plays a big role
> 5) Consider tuning an old AM radio where moving pico farads found your 
> carrier on the AM band.
> 6) As John F. indicated sometimes you resonate initially on a harmonic f.
> 7) Grid coil and grid leak need to be adjusted for a fully loaded 
> secondary
> 8) Grid coil placement and number of turns is tube dependent (usually 
> adjusted by experiment)
> 9) Tuning self C on the secondary with a top load adjustment of 
> different size toroids can put you in or out of resonance.
> 10) Pushing high power can result in grid coil flash over (solved by 
> raising the grid coil to a nodal area or my pancake coil grid under 
> the primary that has a loose coupling to secondary and tighter to primary
> 11) Conservation of energy: To preserve tube life and have ultimate 
> performance the secondary must be in such perfect tune as to use 
> (resonate) as much energy in the tank circuit as physics allows. Any 
> unused goes to heat or picked up in the grid circuit causing many 
> different unwanted things to happen.
>
> For example, I thought my coil was really running great, but just to 
> see what would happen I put on an inch larger toroid, I lost streamer 
> length and the plate got red hot (conservation of energy)
> So, I put on a smaller one by about an in from what I started and 
> streamer length went up 6-8 inches. I had to drop the coil from my 
> work table as it made white hot power arcs to the floor joists on the 
> ceiling on full 140 v variac.
>
> I also use a separate variac and stable filament transformers 
> (scrapped from an AM radio Station) to set the tube filaments to their 
> proper voltage.
>
> Anyhow, that is just for starters from a brain fried from correcting 
> freshman natural science papers.
>
> Thanks to John F. I have a Christmas tree of toroids to choose from. I 
> also picked up an English Taylor metal spinning lathe that I am slowly 
> rebuilding to make various HV terminals.
> I have a TIG welder too so I can produce seamless terminals with some 
> grinding & polishing.  It all just takes time.
> Now its time to hit the sack so I can act rationally in tomorrows 
> morning class until the coffee works.
> I am sure John F. will add to the list.
> John W. G.
>
> John W. Gudenas, Ph.D.
> Professor of Computer Science
>
> On Mar 30, 2009, at 10:29 PM, bartb wrote:
>
>> Hi Dr. John,
>>
>> Dr. John W. Gudenas wrote:
>>> If you are tuned at 250 KHz stay there as you have already 
>>> discovered VTTC tuning is tricky.
>>
>> What is it about VTTC's that makes tuning so tricky?
>>
>> Bart B.
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