Variable AC control (low cost)

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By doing as much of it as possible as small incremental steps, with each st= ep paid for by at least one sale of a completed instrument.

Neither would I, if I'd had a customer to buy any of the intermediate steps= .

Thermal expansion of the diameter of the windings. Have you tried winding t= he wire onto a low thermal expansion former - fused quartz and Zerodur come= to mind

- under enough tension that the wire doesn't expand off the former within t= he working temperature range?

Nickel-Zinc ferrites are good to a few MHz. Fair-Rite claim to go a bit hig= her.

but the permeability seems to rise by about 1000ppm/K. With a big enough ai= r-gap you could get that down to compensate the nominally 150ppm/K you get = with polystyrene, as mentioned in the old Mullard (subsequently Philips, no= w Ferroxcube) data books, but that 150ppm/K is +/-50ppm/K.

-- =20 Bill Sloman, Nijmegen

restrictions prohibit wood fired BBQs) from a stove top. Problem is that sometimes, 1500W is too much and I need to throttle back the temp.

stove but can't find anything local. A new one is in the 70-bucks range and that can't happen.:)

opening and closing a vent to let heat escape as cooking times can often be in the ten to twelve hour range.

that with 1500W? I am using that in the smoker now, but it does not get quite hot enough so that control is always on max.

How about this controller & a SSR?

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wire onto a low thermal expansion former - fused quartz and Zerodur come to mind

working temperature range?

air-gap you could get that down to compensate the nominally 150ppm/K you get with polystyrene, as mentioned in the old Mullard (subsequently Philips, now Ferroxcube) data books, but that 150ppm/K is +/-50ppm/K.

I did play with making my own inductor for the 50 MHz oscillator, using a Fair-Rite toroid, but it wasn't worth the hassle.

I wound up using a Coilcraft Maxi-Spring, good Q, cheap, tempco compensated very nicely.

Did you have to quote 200+ lines to post this?

Sorry, that core was MicroMetals, not Fair-Rite.

--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com

Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation

Was that mix 26, or is the back side...clear/gray/black?

Mix 26 ends at... hell... it's hardly useful at 20kHz, at least any any power level. Based on my experience with #26 and 52, I find it hard to believe any powdered iron is useful in the MHz, but I guess I should get some #2s and such and see what their Q is really like.

IIRC, Fair-Rite #33 is temp compensated. It's a fairly mediocre ferrite, but claims very stable permeability. Commonly seen in "loopstick" rods.

Tim

-- Deep Friar: a very philosophical monk. Website:

My home-made powdered-iron toroid had a Q of 72 at 46 MHz. I'm not sure what mix that was. I could look it up if you're interested.