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R: [TCML] First light, small VTTC
Hi John,
You said that the primary has 19.7 turns of 16awg wire, how method do
you use to tune the system? I normally use magnet wire also for the
primary 19awg or two or three smaller paralleled between, and I use a
spacer (another magnet wire of 24,26awg) that I remove at the end of
winding. Then I scratch the enamel on the last windings and look for the
best tuning. But how do you succeed with an insulated wire? I'm curious
for the number 19.7!!
Cheers
Vladi
-----Messaggio originale-----
Da: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] Per conto
di futuret@xxxxxxx
Inviato: martedì 28 ottobre 2008 23.34
A: tesla@xxxxxxxxxx
Oggetto: Re: [TCML] First light, small VTTC
Vladi,
There are so many factors to consider. Some tubes need more feedback
than others. My experiment was to test the idea of using a high
position for the grid coil which some folks have found helpful. So
far in tests with this small coil I didn't see any advantage but of
course this coil still needs more optimizing in general.
I used 19.7 turns on the primary I think, and the coil height is about
2" of 16awg wire. The secondary is 2.5" x 8.875" wound with 28awg wire
for about 620 turns or so. No toroid. The grid coil and primary are
both 4.75" dia. The grid coil uses 20 turns of 24awg magnet wire tapped
at 12 turns. MOT is a small 2000V unit with level shifter. Filament
transformer is 6.3V output, so I use a 50 ohm dropping resistor on the
120V input to drop the output to 5V for the 4-125A vacuum tube. The RF
bypass cap is 0.001uF at 5kV mica, the grid leak cap and filament bypass
cap are both 0.001uF at 2.5kV. No staccato.
John
-------------------
-----Original Message-----
From: Vladimiro Mazzilli <V.Mazzilli@xxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Tue, 28 Oct 2008 5:07 am
Subject: R: [TCML] First light, small VTTC
So seems better to use thin wire to have a good grid driving, but not
too tall
in order to no decrease the spark length?
Vladi
----------------
I powered up my new small 4-125A VTTC and got 4" sparks
so far. They are the fuzzy type sparks. More tuning is needed. I tried
removing the MOT shunts, but the sparks didn't get much longer so far.
The tube plate gets red which is not surprising for a 4-125A tube. I
tied the grids together on the tube, and I'm using 1500 ohms for the
grid leak R. I tried 2500 ohms but that gave very weak sparks. On a
previous coil which used a 4-250A tube, I got the same spark output with
grids tied together as when feeding the screen grid from a dropping
resistor. That coil also used a 1500 ohm grid leak resistor. There is
no toroid on the coil. Some tests I did in the past showed that even
the choice of vacuum tube type can make the sparks either fuzzy or
sword-like. This may suggest that some parameter was not optimized for
each tube.
I did a quick experiment with a raised grid coil. Normally
I allow about 1/2" space between the primary and grid coil.
I raised the grid coil by about 3" as a test. The sparks
got much weaker. So I moved the grid coil tap so I used
20 turns instead of 12. This increased the spark length
almost to what it was with the lowered grid coil. This secondary is
only 8.875" long, so raising the grid coil by 3" is a lot for this small
coil. I tried various grid coil heights and generally speaking, the
spark output varied with the grid coil height. A higher grid coil gave
weaker output sparks. These results are preliminary because the coil
still needs more tuning.
Cheers,
John
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