Whiteboard - SSTC
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1)
June 20, 2004. Tesla List. Original poster:
humanb@chaoticuniverse.com
Hi, can someone tell me just how much more power a H-bridge can process over a
Half-Bridge? It's not just 2X as much is it? It isn't that simple, is it? Also,
what would be the best way to calculate the optimum Capacitance in the voltage
divider for a Half-Bridge? Currently I am using two 1uF caps, but when
running a resonant tank one may want to adjust this, so I would like to find a
way to calculate the optimum balance. Thanks, David T.
6-25-04
sgsparky@prodigy.net
Hi Jim, I just found this website,
http://www.classeradio.com/
http://www.classeradio.com/ and talk about
information overload! Everything you want to know about the use of MOSFETs in
transmitters and were afraid to ask! This is Steve WA1QIX's website. He is
somewhat of a pioneer in using this technique in Amateur radio applications, at
least on the East Coast of USA.
From what I see on this page PDM (Pulse Duration Modulator) and PWM (Pulse Width
Modulator) is the same animal.
This page looks like a valuable resource for those of us that want to modulate
our coils. Sue.
From:
"Tesla list"
Date :
Wed, 14 Jul 2004 19:45:25 -0600
Subject : Re: All who know VTTC stuff ;-).
Original poster: FutureT@aol.com
In a message dated 7/14/04 7:39:40 PM Eastern Daylight Time, tesla@pupman.com
writes:
>Original poster: Kreso B.
>
>Hy i would have 7 questions.
>
>1. How to determine is the VTTC in perfect tune or is it not? Kreso,
You can build a variable capacitor or change the capacitance by adding or
subtracting small capacitors to change the capacitance in small steps to see if
the spark length improves at any point.
You can also change the primary tap point. However you must be aware that this
changes the tank impedance and may cause changes unrelated to tuning. Small tap
changes will reflect tuning changes more than impedance changes especially if
the tuning is close to begin with.
Another way to check tuning is to vary the size of the toroid. If the
sparks get longer with a smaller or larger toroid, then the tuning was probably
not quite right originally.
Interestingly, the tuning if it is close will not affect the spark length,
however the tube will run redder for that spark length. In other words
better tuning may not lengthen the spark, but will make the tube run cooler and
reduce the power draw. I'm assuming you want to tune for longest sparks
with minimal input power.
Adjustments of grid feedback, grid resistance, tuning, coupling, etc, tend to
interact. Much adjustment may be needed before optimal results are
achieved. My best VTTC's achieve an "efficiency" of: (without staccato)
spark length inches = 0.5*sqrt input watts.
>2. If the secondary is wound sloppily and has many knick does this influence the
spark length?
Probably not much influence.
>3. If i will rewind the secondary with same number of turns but without
nicks
and overlaps, will i have to retune it?
Probably the tuning will be very similar.
>4. I just noticed the tube has a small air bubble in glass ( I could post a
picture). It works perfectly, but should I be worried?
Probably this is not a problem.
>5. If the filament transformer is rated fro much higher current than the tube
needs can it do any harm ( my tube needs 5 V 14.1 A i have 5 V 30 A).
Current rating doesn't matter as long as it's enough. What matters is the
voltage. The tube will only draw the rated current if the voltage is correct.
>6. Will staccato improve spark length? On my SSTC it improves it by ~200 %.
It depends. Sometimes it won't help, other times it will. By using staccato,
you can increase the peak power but keep the average power low for longer
sparks.
>7. Will an improper diode
decrease performance? I currently have 6 diode >bridges in series ( greatzes).
I guess this if for a voltage doubler or level shifter? Probably not a lot of
effect on performance will be seen. Operation on filtered DC without staccato
will cause the sparks to be short, but draw terrific power. Raw AC operation
with staccato tends to be efficient. Staccato can be used with filtered DC but
is tricky to implement. Staccato is easily implemented using a mechanical
rotary switch from the filament to ground. If the tube is a tetrode, an AC 50Hz
sample of the power line can be fed to the screen grid to simulate AC operation
and make electrical staccato operation easier.
Do you ever get the very straight sword-like sparks such as can be seen at my
website? (in the staccato mode)
http://hometown.aol.com/futuret/page3.html
http://hometown.aol.com/futuret/page3.html
click on tube coils (I think). John
>Thanks for answers, Best Regards, Krešo B.