RF parts for dynamic fusor

For Farnsworth type designs.

RF parts for dynamic fusor

Postby Doug Coulter » Wed Mar 19, 2014 3:49 pm

I built a "Tank coil" transformer for the main grid, to allow perturbations there to produce a drive signal for the "ion source grid". I mentioned this in a thread on theories and speculations. There are a lot of possible operation modes, from oscillation at various frequencies (perhaps more than one at a time), to simply stabilizing things "at the edge of light-off pressure", where a "going out" of the main grid increases the bias on the ion source grid, and lights things back off again. Should be fun! We can of course, tune this by messing with either the phase of the connections, or by putting capacitors in series or parallel with the secondary (the primary connections - forget it, too dangerous and hard to get at in operation).
I wound these with very roughly a 4::1 turns ratio. I get that as an unloaded voltage ratio on the bench from about 2.5khz up to around 25 mhz (limit of test) which is darn good for a wideband transformer. I also have enough bits of type 61 ferrite to insert to increase the primary inductance by about a factor of 4 should we want better efficiency at lower frequenices, or enough type 77 (with use of a hammer to make pieces small enough to fit) to go much lower yet if needed.

I'm just now in the process of hooking all this up. You can see a mockup here:
https://www.youtube.com/watch?v=dnJw6Y7 ... l009sYggjA
Skip out to about 4:08 to see it.


Here's a couple detail pix.
Mockup1.JPG
Mockup, but not ready yet

This just shows how it all goes together. The primary, fine pitch, fits into my innie-outie 1.1" HV fittings, held with setscrews, and is "ready to go" right now. The secondary I had mental issues with "how am I going to get solid mounts for the wire ends that will stand a bit of bashing when I put the outer shield pipe on? Don't want to drill holes for sneak-path arcs in that super expensive PVC sched 80 pipe...so look what I did instead. The pipe underneath it all is for a blower that cools the end of the feedthrough and other things inside the fat PVC pipe. What looks like coils in that are actually plastic, not conductive...I tore one up to check that.

Secondary.JPG
Lugs tapped into glued on PVC pieces, sideways, and male/female fitting so I can attach wires without turning and stressing the secondary wires.


So, almost ready for smoke-testing. I have to do a bit of work on a similar sructure on the ion source grid (junk inside a shield pipe) to make a spot to hook this in series with the DC feed, or cap couple with one end of the secondary grounded, or....we don't know what, if anything, is going to work out here.

Remember, we have several kinds of charge/mass species in there. Perhaps we find a frequency (or two) that wave the electrons (and ions at a lower frequency/speed) around such that we get things just so for net Q. That's the hope.
Those still waiting to be registered here, please be patient - it's hard to want to spend a lot of time at the computer when it's "this close"....whether it works the first time, the nth time, or never - I learn something to share, we all benefit.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
User avatar
Doug Coulter
 
Posts: 3515
Joined: Wed Jul 14, 2010 7:05 pm
Location: Floyd county, VA, USA

Return to Fusors, Farnsworth type

Who is online

Users browsing this forum: No registered users and 1 guest

cron