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Registered Member #2485
Joined: Fri Nov 27 2009, 02:31PM
Location: Germany
Posts: 11
Hi,
I'm new here in the forum.
Today i build this little Vttc. I'm using a QQE03/12 ,a double tetrode with max 12W. It runs on 325V at 20W. The resonanzfrequenzy ist around 12Mhz or 13Mhz
here ist a picture of it: (i don't know if the picture is too big?)
a video on youtube:
the schematic i used:
sorry for my bad english, my motherlanguage is greman
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Yea, it is just a simple oscillator and a resonator... Feedback from an antenna. That is somewhat like mine with the 811A, but due to the lower gain i used a single feedback turn for magnetic coupling.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I was just going to send you a PM HFsstc-freak, but it may help other's out. Also, mb, if you ever come across a circuit you have made like this that is not getting strong enough feedback, you can use magnetic coupling...
I put the single turn about 3/4 up the secondary which was on 1.4 inch cardboard tubing, and the feedback (thickness not critical, i used about 28) was on a 2.2OD PCV pipe. If there is too much feedback, use less turns or some method of current limiting. You can tell if you have too much feedback if either the grid is getting red (grid should *never* get red at all), and bad plate heating caused by switching the tube on hard.
A word of advice, never use PVC for one of these. It is very lossy, and I suspect i had a good deal of dielectric heating. Even though dielectric heating is normally done from 300MHz to 3000MHz, i think my 30MHz could have had a bit. My PVC kept melting, and it was not convection heating or corona formation...
Registered Member #1223
Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133
btw, that original "plasma tweeter teslacoil" is using CAPACITIVE feedback. Its not inductive although there is single loop of wire around break out point. It doesnt have to be loop, it can be like piece of aluminium foil close to the coil.
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Mini VTTC
