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Futterman Class C oscillator?
Futterman Class C oscillator?
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Old 16th February 2017, 09:05 PM   #11
woodrough is offline woodrough  United States
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Quote:
Originally Posted by Koonw View Post
The output from "out" of last sch is 50kv( or up to 1Mv or more), is a carrier freq 220kc, far from audio, no difference from carrier generated by class c oscillator, apart from efficiency, I think Class AB is not very low efficient, as long as it solves your problem. There are many just use AC spark gap. 6c33c goes up to about 1Mhz at least. I try to figure up what freq your gears work on later.
Woah 50kv or more that the tube can handle?
I'm more interested in the speed of current the primary coil can convey. The Hyatt resident rise of voltage happens in the secondary coil, which is loosely inductively coupled to the primary. Real pressure magnification happens here. The power it can maintain is largely dependent of the Q factor of the secondary.
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Old 16th February 2017, 09:44 PM   #12
woodrough is offline woodrough  United States
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Old 17th February 2017, 12:01 AM   #13
Koonw is offline Koonw
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The high voltage I mentioned is the step-up transformer output, which is the tip of coil in your drawing, 6c33c can handle 400v if power diss is 30W. The highest power output of a pair of 6c33c oscillator in the configuration in class AB is no more than that of audio amp, about 30W. I have posted a 600W sch for output stage here
but has to be driven by suitable driver, the efficiency is about 60%.

A single transmit tube like 813 you can get 1KW in class C, maybe not be as osc, but have to be driven properly by suitable driver, it should be efficient. What power output is commonly required in relation to spark gap for carrier type? I read that is kilo-watts for AC spark gap type. Do you have sch of high power carrier type?

Edit: I found one 813 VTTC

Last edited by Koonw; 17th February 2017 at 12:09 AM.
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Old 17th February 2017, 04:18 AM   #14
Koonw is offline Koonw
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I now figured out that at 1.26Mhz, the input impedance of primary coil is 320k. So make me wonder why you think you need to lower output Z of your oscillator, unless you also say the output Z is great than 320k. The output Z for 6c33c totem pole is about 60 ohms, I am not sure about Class C, unless I got the actual sch to compare with, is it like you first post?
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File Type: png Tesla Coil test-1.png (59.9 KB, 35 views)

Last edited by Koonw; 17th February 2017 at 04:21 AM.
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Old 17th February 2017, 05:30 AM   #15
woodrough is offline woodrough  United States
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Oh! I forgot to mension that my primary coil was made for the 811a amp, which needs a higher impedance primary. It's a 2" high 20" diameter coil that has 9 turns.

The primary coil that I want to use (which I forgot to list here) is a single or double turn primary that I built that is a little bellow .01mH. (It's a 20" diameter 3" high flat strip coil, a virtual short).

What would the impedance be like for something like that at resonance?

Also thanks for running these numbers/simulations. I haven't delved into that yet still a rookie in some places

Less turns the better in this application.

Also I'm interested in an oscillator that can drive such low impedance for other experiments in the future. A do all oscillator! That's why I was remotely curious about a driver stage for controlling frequency of triggering

Last edited by woodrough; 17th February 2017 at 05:36 AM.
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Old 17th February 2017, 06:12 AM   #16
woodrough is offline woodrough  United States
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I only say class C because of efficiency due to minimal conduction time. Impulse like behavior.

So class AB doesn't really bug me :9

And yea, I refer to the 811a schematic in the first post as the class C layout.

Last edited by woodrough; 17th February 2017 at 06:14 AM.
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Old 17th February 2017, 06:45 AM   #17
Koonw is offline Koonw
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For 0.01m pri. inductance, input Z drops to 34K, impedance goes up as inductance get larger I also plot a few other values.
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File Type: png Tesla Coil test-3.png (61.0 KB, 29 views)
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Old 17th February 2017, 07:51 AM   #18
Koonw is offline Koonw
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Well I do some more sim and found that this totem-pole can also do Class C. If you bias very low say to -200V, there is very little current flows so it's close to cut-off. Then you increase the amount of feedback (I use sig, gen) until the tubes start to conduct, wow there you are. What do you think? See if we can build the actual circuit if you're still interested. Sorry to jump to conclusion too early .
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Last edited by Koonw; 17th February 2017 at 07:54 AM.
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Old 17th February 2017, 09:58 AM   #19
Kay Pirinha is offline Kay Pirinha  Germany
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In my understanding of the Tesla Coil, it's all about resonance. You can't deliberately choose any carrier frequency. Starting point has to be the secondary winding, as it's wire length determines lambda/4 of the carrier frequency (maximum voltage at the top, zero voltage at bottom/ground, current vice versa). Then the secondary's inductance, together with the ball, or toroid, at it's tip forms a serial resonant circuit. So you have to tune the ball's/toroid's earth capacity with the secondary's inductance to meet the given resonance frequency. Next the primary winding has to be paralleled by a capacitor as a parallel resonant circuit, also meeting the carrier. Paralleling usually is done by means of an arc gap.

Using tubes or other active devices, you actually have a transmitter's power stage. Thus I don't see any use in push pull, including the totem pole/OTL and the Circlotron designs. Just parallel a number of tubes to the desired output power (usually measured in arc lengh) and build a class C self oscillating PA!

Best regards!

Last edited by Kay Pirinha; 17th February 2017 at 10:02 AM. Reason: HTML stuff...
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Old 18th February 2017, 06:19 AM   #20
woodrough is offline woodrough  United States
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Quote:
Originally Posted by Koonw View Post
Well I do some more sim and found that this totem-pole can also do Class C. If you bias very low say to -200V, there is very little current flows so it's close to cut-off. Then you increase the amount of feedback (I use sig, gen) until the tubes start to conduct, wow there you are. What do you think? See if we can build the actual circuit if you're still interested. Sorry to jump to conclusion too early .
Oh fantastic! This was the validation I was looking for c:

The only question I have is on the driving section.
Is there a more simplistic/easier/lazy'er way of driving/phase-splitting a signal than that originally shown in the first post with 12au7's in the futterman schematic?
(are solid state solutions clumsy here?)

It would be kinda fun to switch between bias modes depending on the applications. audio listening vs antenna transmitting

The signal generator Im using currently is:
25MHz Dual Channel DDS Function Signal Generator Arbitrary Wave Sweep + Software | eBay

15Vp-p with not much current handling capacity of course. I wonder if the grid can be driven by this 15 volt signal and a hand wound step up & phase transformer... (since the impedance in the grid is so low?) This idea is perhaps too lazy...

Quote:
Originally Posted by Kay Pirinha View Post
In my understanding of the Tesla Coil, it's all about resonance. You can't deliberately choose any carrier frequency. Starting point has to be the secondary winding, as it's wire length determines lambda/4 of the carrier frequency (maximum voltage at the top, zero voltage at bottom/ground, current vice versa). Then the secondary's inductance, together with the ball, or toroid, at it's tip forms a serial resonant circuit. So you have to tune the ball's/toroid's earth capacity with the secondary's inductance to meet the given resonance frequency. Next the primary winding has to be paralleled by a capacitor as a parallel resonant circuit, also meeting the carrier. Paralleling usually is done by means of an arc gap.

Using tubes or other active devices, you actually have a transmitter's power stage. Thus I don't see any use in push pull, including the totem pole/OTL and the Circlotron designs. Just parallel a number of tubes to the desired output power (usually measured in arc lengh) and build a class C self oscillating PA!

Best regards!
One of the reasons why I want to be able to input my own frequency vs be phase locked with the secondaries secondary coil (via tickler) is to be able to have more control over the different resonance modes. For instance, a grounded resonator can resonate at 1/4λ, 3/4λ, 5/4λ, 7/4λ... while a free resonator will resonate at 1/2λ, 1λ, 3/2λ, 2λ, etc.
Lately I have been finding it pretty insightful to have control over what mode of resonance a coil is in.

Futterman Class C oscillator?


Manually adjusting the input frequency also comes in handy for experiments involving concatenated coils. (Two coils serial connected coils that are not magnetically coupled to one another) This is a subject matter that gets irritating with Tickler feedback circuits.

The 6c33c totem pole design sparks my curiosity because it can handle darn low impedances. Primary coils are most effective with the least number of turns possible, demanding for a low impedance transmission circuit to drive it.

Last edited by woodrough; 18th February 2017 at 06:47 AM.
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