Re: air-core resonator

["Steve" <Steve-at-g8cyerichmond.freeserve.co.uk> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

You've got a good start for flybacks. The ferrite is needed to maintain the
magnetic circuit. Actually there are air gas in the ferrite ring, usually
formed from  thin pieces of silicone sheet. The resonant frequencies of
these transformers are in the 15-20kHz range (it depends on a number of
variables). I have built a number of flyback (in the UK they are often
called LOPT) circuits, and use them to drive small Tesla coils. The commonly
used drivers with either 2N3055s or 2N3055s with 555 timers wouldn't work
with air cored transformers as the frequencies needed would be too high for
the 2N3055..

Basically to drive a small Tesla coil, I take the output via a high voltage
rectifier to feed the primary circuit. Either EHT rectifiers reclaimed from
TVs or a string of 1N4007s are ok. My best effort so far has been 6" sparks
using a small LOPT with a pair of 2N3055s, feeding a primary circuit with
8.3nF MMC and a helical primary 4" dia. 18swg wire, 6turns 1" high (ok a
pancake would be better). Secondary is 2" dia 12" high 850 turns close
wound. Topload 2" x 9.5" toroid. The secondary is really a bit too long and
thin. The flyback circuit draws about 3A -at- 18V peak.
I could probably improve things by using a larger flyback transformer, and a
bridge rectfier rather than half-wave.
Steve.
----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, August 02, 2000 12:04 AM
Subject: air-core resonator


> Original poster: "sundog" <sundog-at-timeship-dot-net>
>
>
> Hi all!
>
>  I'm looking at flyback drivers for giggles and experience, and am
> wondering... I've seen a lot of methods of re-wiring them with a new
> primary, and a feedback winding to make it self-oscillating.  Please
excuse
> my ignorance, but will this method work on an air-core resonator, or is
the
> ferrite core needed?  I'm guessing it is needed.  I've got a 16v
> some-ungodly-amperage transformer to push it with (the thing is
> center-tapped, and about 3"x4"x4"!), and a good 5lbs.  Don't need caps to
> explode wire, I just short that thing out, and *poof!*.  Anywho, I've got
a
> good high-amperage supply, and plenty of 2n3055's to toast.  Got good
> heatsinking also.  Eventually i'd like to take a crack at a solid-state
> sillycon powered TC.  I believe flybacks would be a good place to start
> learnin'.  Less noise than a sparkgap too :)
>
>   Another question...A base-fed TC...that's just a secondary that's having
> high-powered RF pumped into it, right?  I'm assuming a primary isn't used,
> and the normal RF ground is used as the input.  What are the normal ranges
> for input power, and how exactly do you feed it?
>
> Caio!
> Shad
>
>
>
>