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ragnar

Tue Aug 08 2006, 03:05AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

hi all,
just wanted to post a couple of pics of what I've been working on lately:

The "smaller" coil (with the neat primary) runs at ~3MHz and would have been drawing ~150W in this photo.

The "larger" coil (with the thicker wire) runs at ~6.5MHz and was drawing the same power.

Each of these is a stepping stone to a high power 12MHz coil. The former will be thick-walled Teflon tube, because Acrylic and PVC suck.

Both use a single IRFP450 running in class-E configuration with resonant-circuit gatedrive.

...

Tue Aug 08 2006, 03:40AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Looks good BP

Will you be the first one to beat EVR's 10.1MHz sstc?

A tip for those primaries... As you are winding put a small amount of superglue (CA glue) on the coilform then wind the wire. Then you don't need those wireties

You can also wrap the form in waxed paper and use more glue (it works a lot better if you have several layers that you can glue to eachother) and you can have a formerless coil too.

Keep it up!

BTW, did you ever get audiomodulation going on the OMFGSTFUHFSSTC?

ragnar

Tue Aug 08 2006, 08:56PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Ya, I didn't have any cyanoacrylate at school, I usually superglue my primaries and remove the former =P

This also wouldn't have happened if I hadn't dug through my stash of "dead" MOSFETs and found one that did indeed work. I'm almost completely out ^^

My gatedrivers get warm, but the heatsink on the IRFP450 stays cold.

Just yesterday I found some heatsinks big enough to allow me to try audio by amplitude modulation. There goes my efficiency

Marko

Tue Aug 08 2006, 09:35PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Bother. I didn't do much of work on my Class E coil lately.

(Rather having some 'fun' with holidays. :p )

How many mosfet's have you fried yet bp?

I think the 'Anticoil' is only thing that can have reasonable Q at that high frequencies, and also cooling is much better.
I use to fill a PVC ube with poliester resin to prevent it from falling apart once it gets stinking hot, but then connection under poliester usually goes open

Part Scavenger

Thu Aug 10 2006, 12:23AM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Sweet BP! That thing looks great!

ragnar

Thu Aug 10 2006, 11:15AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Thanks :)

I'm not sure which impacted more, dielectric heating of the PVC former or I^2.R losses on the skimpy 0.15mm copper wire.

Either way, I now have thick-walled teflon PFA primary and secondary formers. It has a nice low loss tangent, and I'm winding the bugger with 0.5mm NOT-solder-through enamelled copper wire.

The best I can do for the primary is 1mm thick solid copper with 1mm-thick (radius) PVC insulation.

Can't wait to wind, terminate, and fire 'em up.

Marko

Thu Aug 10 2006, 01:04PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

*shutter*

lol...

ragnar

Thu Aug 10 2006, 01:54PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

LOL, trying to drop a hint at me? =P

If you really want, I'll send you my artwork for the antiformer. I went to meticulous detail to ensure that each slot was raised 1/8th of the turnpitch, and that kind of thing. It was quite elegant, if it wasn't so vain. ^^

On more practical matters, I've wound the first teflon former with ~220 turns of the 0.5mm copper. Pretty. =)

Marko

Thu Aug 10 2006, 02:16PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hm, now you stole my idea about winding HF coils on round formers.. partly at least =)

Longer ago I tought about using a big multifilar braid of wires wound around a pvc tube, but that would require large number of separate wire sources, and twisting few tens of them together in wanted length would also be a pain.

Winding it the way you did on last pic is easier but I doubt you'l get a big Q increase with low number of very thick wires (you can always try it).

I want some really low impedance here, maybe even a possibility to drive e resoantor directly without a primary on reasonable voltages.

The funny wooden thing I had here is dipped in poliester for fixing, but plywood is ofcourse too chippy to make fine edge carvings. I didn't really care how is it going to look afterall (since I had no chance to make something similar out of acrylic like your form).
It was raather aresult of boredom (poliprojectitis) than some very practical use.

More serious thing I can try would be using some kind of mould and fiberglassing it, but that was too much work :p

ragnar

Thu Aug 10 2006, 02:32PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

wrote ...
Hm, now you stole my idea about winding HF coils on round formers.. partly at least

Done number two... the great thing about my coils is they take so little time to wind =-D

I've got no idea what frequency these'll resonate at. I just hope it's less than 6.5, because that was a little tricky, and tweaking four of them at once won't be fun. =P

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