Magnetic amplifier

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Postby Harry Dalek » Sun Apr 28, 2013 7:01 pm

I have worked on this mechanical clock today spent more time finding parts than putting it together , but almost there just finished the power supply .

The first transformer is for making the DC power supply part for controlling magnetic amp and in this first case AC as well for my first go at one i had the idea i can use the 50hz and the voltage and the second transformer i might be able to make a simple magnetic amp motor speed controller .

If it works or not we will see worth a shot got to start some where :wink:
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby gary » Sun Apr 28, 2013 7:55 pm

Harry you never cease to surprise me with the "other peoples garbage" solutions you come up with - regardless of the outcome of the experiment there always seems to be a mechanical objet d'art at the end of it.

I hereby pronounce you the Heath Robinson (Rube Goldberg for U.S. members) of NBTV! ;-) And I mean that has a very high compliment indeed.

I must try and get you interested in steampunk some day...
Perfecting an NBTV system is like trying to slam a revolving door...
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Postby Harry Dalek » Sun Apr 28, 2013 9:42 pm

gary wrote:Harry you never cease to surprise me with the "other peoples garbage" solutions you come up with - regardless of the outcome of the experiment there always seems to be a mechanical objet d'art at the end of it.


The worst part is thinking about best way to do it with whats in your just box i am sure my wife would wonder what the hell i am keeping this and that for but as we know we need junk ,i never buy wire its all from old electronics .

I can never be bothered building some thing messy then neat rather try my best first time win or loose and a nice size these days .

I did have another idea for replacing the dc motor yesterday and it slowed me up it was some thing you said in the past just want to see if i could get it to work .

(the use of steppers as synchronous motors as a great opportunity for NBTV)

I Hooked a bipolar stepper motor up to a Ac supply and wanted a pulley system to drive belt drive an un powered motor with the cd disk on that motor just as i could get perhaps a nice speed worked out if it worked the disk went 25 times around to 1 of the stepper motors rotation ,trouble was it was the stepper didn't have enough torque it would not turn the other motor and it was big .

The thinking behind it was it would be in sync with the 50hz so a slow clock rotating a strobe disk to make a higher frequency ..if i got it right.
Dam that torque.

I hereby pronounce you the Heath Robinson (Rube Goldberg for U.S. members) of NBTV! ;-) And I mean that has a very high compliment indeed.


That sounds like a nice honor sounds like they have a bit of steptoe in them as well...need to like junk to reuse it .
:wink:

I must try and get you interested in steampunk some day...
[/quote]

OH i do like steam punk its very clever i suppose NBTV is steam punk in reverse .
i saw a i phone hand cranked charger on a program the other day but not sure i like changing vintage electrics tack on modern bits rather a copy ...i never liked the idea of cutting open a vintage valve radio and turning it into a say a monitor ...a copy i like.... original its like murder to me .

:wink:
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby gary » Sun Apr 28, 2013 10:16 pm

One "trick" you can use with steppers is to "ramp" them up to speed slowly because they tend to have a lot of torque at very slow revs. So if you add a "pulse rate control" it can help a great deal.

BUT! I DID say steppers are an opportunity for NBTV but I also said they have to be good quality steppers - the "tin can" types from printers, and the small ones from floppy drives just don't cut the mustard. Unfortunately good quality steppers are rather rare in Oz (and therefore expensive), and shipping them from OS is expensive - at least the cost of the steppers themselves - because they are heavy beasts. You used to be able to get good steppers out of very old printers and photcopiers etc but they are hard to find now-a-days.

After reading up on some commercial optical choppers I see they are using BLDC motors for high speed and constant speed. They have come down in price enormously in recent years - I have bought one and an ESC to go with it and when I get a chance will try and do some "hacking" with it. The control of BLDCs is *somewhat* similar to steppers.

I am more the "build a messy prototype" and then "build a neat one" person - needless to say I have never built a "neat one" ;-)
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Postby DrZarkov » Sun Apr 28, 2013 11:02 pm

gary wrote:I am more the "build a messy prototype" and then "build a neat one" person - needless to say I have never built a "neat one" ;-)


"To invent, you need a good imagination and a pile of junk." Thomas Alva Edison.
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Postby Harry Dalek » Sun Apr 28, 2013 11:38 pm

One thing on Ac and Dc there is an in between i suppose it must be used in some effect in these magnetic ampc where a cap is not used i see.

Where after diode rectifier the Ac is DC i am wondering what effect this unfiltered DC would have on a dc motor ? is it any different to a a filtered power supply?

Yes gary i think all my steppers are a bit weak its one of those things have to use what you got hope for the best .\\\

On BLDC motors i have had luck once with the laser monitor they have a very high speed more than whats needed for NBTV standards.

Dr Z i wonder what Edison had in hes junk box ? If you asked tesla he would say me !

:shock:
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby DrZarkov » Mon Apr 29, 2013 12:03 am

Just by chance I found this video at "SolderSmoke Daily News" about an Australian ham TV operator: http://youtu.be/C6Xif9hd2Ps

:lol:
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Postby gary » Mon Apr 29, 2013 12:14 am

Blasted cockatoos - they are a bloody menace! They eat all my bird seed in about 3 swallows - then they start on the cedar window frames...
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Postby Harry Dalek » Mon Apr 29, 2013 3:31 pm

Good one Dr Z interesting man i can tell he is not married for the reason he does every thing he wants . :shock:

OH yes the Cockies are lets say the wolfs of the air not much of a problem with my little antennas these days but i am yet to have an apple off my apple tree due to them

OH well home from work early today so i will make good use of the time and do what that bloke did what ever i want :wink:
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby DrZarkov » Mon Apr 29, 2013 4:36 pm

I wonder how my house will look like if I don't marry again in the next couple of years...
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Postby tubefriend » Mon Apr 29, 2013 6:44 pm

I never studied the history of Mr. Baird so i might be wrong in the historic sense, but from own experiments with modulated light i have an clear idea why he used the chopper discs to reduce the effects of the response time limit of the selenium cells.

The cell has an corner frequency somewhere around 10 to 100Hz, the value and shape of the curve variating with absolute brightness, temperature, age and other factors. This is somewhere in the middle of the baseband frequencies.

To use the baseband he would have needed not only amplifiers with an frequency response going down to very few Hz, but also an high frequency boost that is often adjusted in frequency and amplitude to compensate the mood of the cell. Misadjustments would cause ringing and tail effects.

If he instead chopped the light with someting around 20kHz then he was certainly above the corner frequency of the selenium cell.

This would give two advantages, the first would be that the relative bandwith of the amplifiers now needed to be only between something 10kHz to 30kHz and the second that the equalization now changes to an simple raise of 6dB per octave and any variation of the cell would only affect the amplitude of the signal.

The disadvantage would have been that he needed something around 20 to 30dB more amplification because the output is far down the response curve of the cell.

But because of the simplified narrow band amplifiers he might needed not much more tubes, maybe not even one more when he tuned interstage transformers for resonant gain and slope equilization.
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Postby Harry Dalek » Mon Apr 29, 2013 7:05 pm

Heres my first go at the magnetic amp ,it works i find it a little sluggish to start but it does control the speed .
On the lower voltage it needs either a slight kick start or a switch over quick to the 12v to get it to start moving on the lower voltage....then adjusting the pot up and down theres speed movement alright at the higher Ac voltage its harder to tell .
I had a pot across the windings in parallel but at the moment in the testing its in series i put in a 50k so the motor stops on the lower setting...on 12v i find it will not stop which i think is due to the core of the transformer still being magnetized perhaps a 100k might have the same effect as the 50 on the lower voltage and stop the motor ...just being fussy now but i see the effect it works .

I have to point out the transformer i am using for the magnetic amp isn't a true center tap is 17ohm one side and 27 ohm the other the mains transformer is 10 ohm either side ....just gave it a go just to see

Any experiment or changes think might work better ? i have kept caps out of it to see how this went for now...suppose the motor is working on half AC and DC hard to get my head around it ?
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My first go at a magnetic amp dc motor speed control
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby gary » Mon Apr 29, 2013 8:12 pm

harry dalek wrote:Any experiment or changes think might work better ?


Dear me Harry, you are asking us? YOU are already the resident expert on magnetic amplifiers - we'll just sit back and watch with interest I think. ;-)
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Postby Harry Dalek » Mon Apr 29, 2013 9:31 pm

gary wrote:
harry dalek wrote:Any experiment or changes think might work better ?


Dear me Harry, you are asking us? YOU are already the resident expert on magnetic amplifiers - we'll just sit back and watch with interest I think. ;-)


Well i wish i was i will try and learn as i go .

Every thing i have seen on these so far has a thing that can work off AC like a light or speaker ,this motor is DC i can see its working in thats theres speed control but with a normal dc supply it would run faster than it does here and i feel looking at the schematic the negative end should be grounded ...i think perhaps it might be worth a try replace the motor in the circuit with a light globe or resistor leave the positive of the motor where it is and ground the negative ..as the voltage is adjusted to the transformer it should work better....i will try that tomorrow ..
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Postby Harry Dalek » Mon Apr 29, 2013 11:22 pm

I just came across this on magnetic amps and dc load arrrrr i see i will be soldering in 2 more diodes tomorrow .
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Harry Dalek
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