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Old 13th June 2010, 06:06 PM   #31
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Originally Posted by Elvee View Post
You could use the Poulsen principle
There are numerous straightforward ways in which a person with some technical education can make a considerable nuisance of themselves to those in their immediate vicinity, and even those at some remove.

Generally as people educate themselves they develop an awareness of how their activities can impact on others and this is usually accompanied by an element of self-restraint.

For this reason most radio amateurs, for example, are quick to give a few hints to an individual who is obviously striving to expand their technical knowledge, but are less quick to hand over details of how to construct a potentially antisocial device on the basis that owning one would be 'neat'.

w
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Old 13th June 2010, 06:22 PM   #32
Mooly is offline Mooly  United Kingdom
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I'm sorry if I was a bit short in my remarks to you, I hope you will forgive me...

w
Of course... good to see you back on here
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Old 13th June 2010, 06:29 PM   #33
Mooly is offline Mooly  United Kingdom
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Default CivicProtection

OK... I can understand the curiosity value of something like this so, and I think I mentioned this earlier (haven't read through it all again), but why not build it all up apart from the 35khz source and then in the first instance use an old amp or a power IC and variable sinewave oscillator and make sure the thing actually works as intended.
This way you have total control over the HF signal with regards to frequency/amplitude and can determine what works best for your components and magnetics etc.
Then look at ways of obtaining a signal you know works. Although I have zero experience of this circuit (never even heard of it before this) I bet getting the HF at some optimum value is the key to it's success.
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Old 13th June 2010, 07:50 PM   #34
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by wakibaki View Post
There are numerous straightforward ways in which a person with some technical education can make a considerable nuisance of themselves to those in their immediate vicinity, and even those at some remove.

Generally as people educate themselves they develop an awareness of how their activities can impact on others and this is usually accompanied by an element of self-restraint.

For this reason most radio amateurs, for example, are quick to give a few hints to an individual who is obviously striving to expand their technical knowledge, but are less quick to hand over details of how to construct a potentially antisocial device on the basis that owning one would be 'neat'.

w
IMHO, a small gas-filled tube exciting a 35KHz resonant circuit is pretty harmless (to audio devices anyway) compared to mobile phones.
What can you do when 95% of the population is "antisocial".
Are you going to issue ASBOs to PLCs users?
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Old 13th June 2010, 08:11 PM   #35
dmills is offline dmills  United Kingdom
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Another approach:

Take a multipole stepper motor and drive it as an alternator from a suitable motor.
If the motor has a 1.8 degree step angle (200 steps/rev) then for 35Khz you need ~10,000 RPM (Easy with a smallish DC machine).

You could even use saturatable reactors to build a frequency doubler....

Regards, Dan.
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Old 13th June 2010, 09:55 PM   #36
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CivicProtection, I'm not trying to discourage you or disspate some of your interest in magnetic amplifiers, but they were around in the age of vibrator switching power supplies. The reason practical circuits using these techniques are so hard to find these days is that newer technologies made them silly in a hurry long ago. Anyone that's ever used a vibrator switch, except maybe manufacturers of them, was happy to throw them out. Direct electromagnetic generation is probably the cleanest angle. A carefully designed multi-pole generator can supply highly sinusoidal output at high frequencies without very high shaft RPM, lower being quieter. You could look into the axial flux PM designs that are being built for home brew wind power. The examples on the net can be very primitive, but you might understand what you need to do for optimization in your application. Hand buidling high performance motors and generators is a serious project in itself, but it might be hard to obtain anything off the shelf that has quite sinusoidal output. The drive side for the genemotor could be from any over-specified AC induction motor so that it ran essentially synchronous. Large amounts of flyweight might be inherent and some damping in the coupled shaft can help keep drive harmonics out of the driven shaft. What a crazy project.

Last edited by Andrew Eckhardt; 13th June 2010 at 09:57 PM.
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Old 13th June 2010, 10:34 PM   #37
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Originally Posted by wakibaki View Post
most radio amateurs, for example, are quick to give a few hints to an individual who is obviously striving to expand their technical knowledge, but are less quick to hand over details of how to construct a potentially antisocial device on the basis that owning one would be 'neat'.
w
My reason for building such an amplifier is not just because it is 'neat', I would like to see if it could be done. I've built other things, and this is more exotic.
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Old 13th June 2010, 10:46 PM   #38
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Originally Posted by dmills View Post
Another approach:

You could even use saturatable reactors to build a frequency doubler....

Regards, Dan.
Hey I thought of that, but I could only find sparse material on the mag-amp, and nothing on making HF with the same. Any ideas?
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Old 13th June 2010, 11:53 PM   #39
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My reason for building such an amplifier is not just because it is 'neat'. I find the technology to be interesting, and I don't want to bore you going on and on about why I think it is 'cool'.
Also I would like to see if it could be done by me. I've built other things, and this is more exotic.
Dimming a bulb with saturatable reactors is possible, next is to amplify sound.

Last edited by CivicProtection; 14th June 2010 at 12:13 AM.
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Old 14th June 2010, 12:05 AM   #40
dmills is offline dmills  United Kingdom
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IIRC there was an article in one of the UK hobby electronics mags (Elector, E&WW, someone like that) about building a 70Khz transmitter using this sort of thing during the anniversary of Marconi making his first Transatlantic contact.

Basically bias the core to near saturation in one direction with DC, inject the exciter power and as the core runs into and out of saturation you get harmonic generation.

It is not much used these days, active parts providing a much more efficient way to do this.

Regards, Dan.
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