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Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
After having a look at the famous "World's smallest SSTC" thread on the old forums, I decided it could be a fun summer project to build a miniature SSTC. I've got some very thin wire (from a clock mechanism) and I'm going to wind a minimalistic secondary with it. The fRes will be somewhere between 6 and 10 MHz.
Then some time ago ShawnLG said here that he had built a tiny Class E SSTC with a single 2N7000! I got inspired instantly. I decided I could use BS170 instead because it has a little better specs and it's easier to find.
The driver is the toughest part. To get decent drive signal at those multi-MHz frequencies there can't be too many stages between the feedback signal and the MOSFET gate. Practically this means that the feedback must go straight to the gate. This could be done with an Armstrong RF oscillator. This looks like a good choice (but I haven't still figured out what is the 40uH inductor needed for. Anybody feel like explaining?)
Another option would be driving the gate straight from antenna feedback. No, I'm not kidding. The gate capacitance of BS170 is 24pF. At least in theory it should be possible (usually the 74HCxx series have an input capacitance of ~5pF).
I'm not really assuming impressing streamers from this kind of a design. This is just gonna be a proof-of-concept thing with maybe some Watts of input power. It is possible with the tiny transistor if I tune it for Class E operation. And the 9V-battery dream could come true with this kind of coil!
Just some ideas thrown in... I'm going to try it in the summer holidays (I'll have plenty of time then)
Registered Member #1389
Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346
I would say go for it! I've gotten 5-15mm streamers from a D cell 1.5 volt battery, and the corona was in the 3-5 cm range (barely visible, except when a grounded plate was near). It should be more than possible to get a TC to run from a 9V battery. I don't really know how well a SSTC would work, however, because mine was a SGTC.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Well, a 9V is severely current limited. I've experienced this first hand with my own projects, on average you get a maximum of 200mA before the voltage begins to drop off too severely. This is with a fresh 9V alkaline FWIW.
It has to do with the cells being in series, with point contacts holding them together. Its a very bad construction technique but these things *are* made to a price.
You're better off with a 1.5V TC, and a small voltage tripler for the CMOS logic based around an ICL7660/MAX660.
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Single BS170 SSTC
