Magnetic amplifier

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Postby Klaas Robers » Fri Apr 19, 2013 5:47 pm

I know that about 100 years ago mechanical amplifiers were used for hearing aids. This consisted of one "telephone", half a pair of headphones, built directly against a carbon microphone system. So there was only one membrane, on one side the well known magnet system of the head phone, on the other side the coal of the carbon microphone. This was built in a rugged small block and you have an amplifier for telephone like use. A friend of me, when I war a student in the 60's, had such a device and showed and explained it to me. It had the size of about a match box.

I guess that it was also used in telephone networks to overcome the damping of long telephone lines. But I even think that the phase behaviour is too bad to use it for NBTV purposes. I see an integrating behaviour, which will spoil the wave form very much.
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Postby Harry Dalek » Sat Apr 20, 2013 2:28 pm

Hi Klaas

I have seen old movies where they use a Horn for hearing aid using a carbon mic is new to me but .

I have been looking into what they had in the 1880s to make an oscillator even if it wasn't used ...the fact is they all failed on the television systems so they didn't take into account amplifiers or if they did knew little of bandwidth and all the rest of it .

Reason i think back then the magnetic amplifier would of been their best bet to try, the oscillator is a problem as i would like to try the magnetic amplifier but i don't want to use a modern idea ...and you need the bandwidth
Looking into the mechanical way i found a encoder that would do 40khz if spun fast enough.
I am also looking into the neon light oscillator the neon light was invented
but they didn't make an oscillator till last century i think .
So the oscillator part is pretty important and a stumbling block i wish they tried negative resistance could use an old nail . :roll:
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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 DrZarkov » Sat Apr 20, 2013 5:15 pm

Early television experimentators had exactly this problem, that early valves could only amplify AC. J.L. Baird was the first who overcame this problem, by exactly this method: Look at the second wheel in his early television device.
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Postby gary » Sat Apr 20, 2013 7:08 pm

oooo! good point herr doctor...
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Postby Harry Dalek » Sat Apr 20, 2013 10:22 pm

Hi Dr Z just looking at that slotted disk he used different angles but just looking at the system the lens and large number slotted disks are the camera part white nipkow and curved slotted one the monitor ....i see the lens disk and nipkow monitor disk and the curved slotted one are all on the same shaft ...smart no sync there needed.....just the slotted one you were talking has a motor of its own.....

Looks like the white nipkow went missing its not in some of the later photos.

Any one know what frequency that slotted disk was making trying to count them ...well if the slotted disks were needed due to the amplifiers then makes sense why i see no use of them these days i always wondered why they were there and not now .
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Postby Harry Dalek » Tue Apr 23, 2013 11:04 pm

Dr Z got me interested in Serrated Disk Baird used on the camera .
Reading this the disk runs at 5000 rpm.....83hz. and or RPS

I really don't understand why this speed or frequency ?

I am going to have to do a pauline hanson please explain !
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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 » Wed Apr 24, 2013 1:53 pm

Harry, the serrated disk is a "light chopper" which more or less modulates the signal to a higher, and more easily managed frequency. It seemed to solve two problems - that of poor low frequency amplification, and the slow response time of his selenium cells. Note that an electronic version of this method has been used by NBTVA members, with varying degrees of success, in improving the recording of NBTV on tape.

Don't forget that the 83 Hz is then multiplied by the number of serrations to get the actually modulation frequency. Baird has stated this gave him a modulation frequency of between 10,000 and 500,000 Hz. The latter value, whilst being theoretically possible, would probably have been difficult to achieve in practice ;-)

I have never discovered the exact number of serrations he ultimately used. There are 2 related patents relating to this technique posted on this site 235619 and 270222
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Postby Harry Dalek » Wed Apr 24, 2013 6:17 pm

gary wrote:Harry, the serrated disk is a "light chopper" which more or less modulates the signal to a higher, and more easily managed frequency. It seemed to solve two problems - that of poor low frequency amplification, and the slow response time of his selenium cells. Note that an electronic version of this method has been used by NBTVA members, with varying degrees of success, in improving the recording of NBTV on tape.


WOW i see what you mean this is something to come up with back then ..this sounds a bit like a mechanical PWM i wonder if thats another invention of hes .
I have never heard of the electronics being explained i just was thinking it was a simple amp ...it sounds like he used a wide band Am radio ...i think.
I have not heard of a this mechanical idea at all thanks for explanation i was hoping someone knew .

Don't forget that the 83 Hz is then multiplied by the number of serrations to get the actually modulation frequency. Baird has stated this gave him a modulation frequency of between 10,000 and 500,000 Hz. The latter value, whilst being theoretically possible, would probably have been difficult to achieve in practice ;-)


This i didn't understand as well i was thinking why perhaps 83 hz per line and why isn't it used today ,Now this information is really interesting and helpful you get a big Star of this post !

Pauline hanson is enlightened:wink:


I have never discovered the exact number of serrations he ultimately used. There are 2 related patents relating to this technique posted on this site 235619 and 270222


I was trying to count them i see one small one looks around 40 50 ish i have seen a early version large white one which looks double or triple that and this one in the above drawing could count that one in the better down load copy sounds like he was playing around with the bandwidth

Did you say before you moved house you had a made a falkirk transmitter just wondering if so what did you try if you had on that disk .
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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 Don Tomkins » Thu Apr 25, 2013 7:20 am

Steve,
Would it be possible for to scan and post pages 347/348 from the chapter on Magnetic Amplifiers you recently posted,
many thanks
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Postby Harry Dalek » Thu Apr 25, 2013 12:20 pm

Back on to magnetic the amplifier after much reading on the Oscillator problem ...I think we have 2 options to choose from That strobe disk with an LDR and the carbon Arc oscillator all electric and mechanical electric ////
My main thinking on this is there is no point trying a magnetic amplifier if the oscillator is valve or solid state .

I am interested if television could of worked before the triode was invented copper wire motors transformers diodes LDR...Basic stuff that was around at the time .

I am just interested and will experiment a bit for a start to see if i can get the oscillator going of cause i will have to use todays stuff ,i will post up the experiments .
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Postby gary » Thu Apr 25, 2013 12:25 pm

harry dalek wrote:WOW i see what you mean this is something to come up with back then ..this sounds a bit like a mechanical PWM i wonder if thats another invention of hes .


No it's not PWM. It's AM modulation. The base band signal spectrum is shifted up in frequency by the frequency of the carrier which, in this case, is the frequency of the light being chopped by the serrated disk. Look up AM Modulation esp. chopper modulators.

harry dalek wrote:I have never heard of the electronics being explained i just was thinking it was a simple amp


Well it was a simple amp (by today's standards) but even modern amplifiers have a response that falls off at very low frequencies. Shifting the baseband up brings it into the "sweet spot" of the amplifiers response curve - look up a typical amplifier frequency response curve - you will see what I mean.

Harry, I just realised that we have been over this before here:
http://www.taswegian.com/NBTV/forum/vie ... highlight=


harry dalek wrote:I was trying to count them i see one small one looks around 40 50 ish i have seen a early version large white one which looks double or triple that and this one in the above drawing could count that one in the better down load copy sounds like he was playing around with the bandwidth


I have seen and photographed the Falkirk transmitter (it's controversial as to it's originality) when it was in the British Museum - I have lost those photos unfortunately - when I went to see it again it had been moved. I was told it had gone to the Museum Of the Moving Image in London and I have photos of that but I am sure it is just a replica - on that machine the number of slits on that machine is exactly - wait for it - 32!

Unfortunately I am pretty sure that the Falkirk system was never shown or photographed in it's working state as Baird wanted to maintain secrecy on the details so I am not sure you will ever be able to ascertain the exact number of slits he used - and I would easily lodge a bet that he used several versions each with a higher number of slits as better engineering skills became available to him. It wouldn't be long before he ditched the concept completely as better light sensors became available to him.

harry dalek wrote:Did you say before you moved house you had a made a falkirk transmitter just wondering if so what did you try if you had on that disk .


Not quite, I did say that my early attempts at building a camera/monitor were based on the Falkirk system - because that was all I had to go on at the time - this was in the late sixties or very early seventies and all trace of it is now long gone - and - like Baird - I never documented. I did have a single nice photo but that somehow got all scrunched up and torn and eventually lost or thrown away.

The number of slits I used would have been a bit of a guess as my knowledge of AM modulation at the time would have been rudimentary - I was only 16 at the time - but, of course, the EXACT number is pretty irrelevant - ideally you want the number (and speed) as high as possible and at least enough to give a chopping frequency higher than the highest frequency in the signal but any number will shift the signal spectrum upwards. You certainly, though, do not want so many that the frequency extends beyond the frequency response of the transmission medium (including amplifier).

Baird did NOT invent this technique but was the first to apply it to this purpose, and he claims, at the high frequencies required.
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Postby Steve Anderson » Thu Apr 25, 2013 1:45 pm

Don Tomkins wrote:Steve, Would it be possible for to scan and post pages 347/348 from the chapter on Magnetic Amplifiers you recently posted, many thanks. Don

How in heck did I miss those pages? I will upload a revised, i.e. complete version as soon as I can get my scanner to co-operate! (It only has 'doze drivers).

I assume you actually mean p348/349?

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Postby Harry Dalek » Thu Apr 25, 2013 11:12 pm

gary wrote:
No it's not PWM. It's AM modulation. The base band signal spectrum is shifted up in frequency by the frequency of the carrier which, in this case, is the frequency of the light being chopped by the serrated disk. Look up AM Modulation esp. chopper modulators.


Its a very clever idea he was a man with a goal alright...i will google the chopper modulators learn a bit more .


Well it was a simple amp (by today's standards) but even modern amplifiers have a response that falls off at very low frequencies. Shifting the baseband up brings it into the "sweet spot" of the amplifiers response curve - look up a typical amplifier frequency response curve - you will see what I mean.



Are there a circuits of hes work any where Gary its sad if he didn't do schematics ? The amplifier and such camera monitor idea as you say must of got changed with every new idea .\

Harry, I just realised that we have been over this before here:
http://www.taswegian.com/NBTV/forum/vie ... highlight=


Oh and even the same drawing but do have a high quality version above !
have to go over them if the curved line disk at the monitor end is talked about.



I have seen and photographed the Falkirk transmitter (it's controversial as to it's originality) when it was in the British Museum - I have lost those photos unfortunately - when I went to see it again it had been moved. I was told it had gone to the Museum Of the Moving Image in London and I have photos of that but I am sure it is just a replica - on that machine the number of slits on that machine is exactly - wait for it - 32!


Pretty sure the old photos its over 32 slits i would like to see that photo of baird standing next to it in the Museum and check the later photos .....the nipkow for the monitor is gone or is that just a later camera .....

Unfortunately I am pretty sure that the Falkirk system was never shown or photographed in it's working state as Baird wanted to maintain secrecy on the details so I am not sure you will ever be able to ascertain the exact number of slits he used - and I would easily lodge a bet that he used several versions each with a higher number of slits as better engineering skills became available to him. It wouldn't be long before he ditched the concept completely as better light sensors became available to him.


It does look like he changed them the one with the lower number looks improved over the large number white one ...i will check any photos from now on i see of this .


Not quite, I did say that my early attempts at building a camera/monitor were based on the Falkirk system - because that was all I had to go on at the time - this was in the late sixties or very early seventies and all trace of it is now long gone - and - like Baird - I never documented. I did have a single nice photo but that somehow got all scrunched up and torn and eventually lost or thrown away.


I recall you talking about it but at the time had no idea what type of he's work it was .
Tend to know better these days not to chuck stuff away i find you always come back to it or want it after its gone....
Pity theres no photo ! i have nothing to show of my first go either but a memory .

The number of slits I used would have been a bit of a guess as my knowledge of AM modulation at the time would have been rudimentary - I was only 16 at the time - but, of course, the EXACT number is pretty irrelevant - ideally you want the number (and speed) as high as possible and at least enough to give a chopping frequency higher than the highest frequency in the signal but any number will shift the signal spectrum upwards. You certainly, though, do not want so many that the frequency extends beyond the frequency response of the transmission medium (including amplifier).


Sort of answers a question to wide a bandwidth is just as bad as to little ,i see with the Carbon Arc oscillator could get to a mhz range i want to try the strobe chopper idea first .
What i am wondering as i expect drifting and what effect that would have have on a magnetic amplifier ...since its also controlling the voltage so bandwidth swing and voltage swing...if at the end its a bit like watching a dx tv signal i am fine with that ..
A magnetic amp bistable flip flop encoder motor control is a bit beyond me yet .
:wink:

Baird did NOT invent this technique but was the first to apply it to this purpose, and he claims, at the high frequencies required.


I am glad i asked i always wanted to know what those extra disks were .
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Postby AncientBrit » Fri Apr 26, 2013 6:03 pm

Slightly off topic maybe but if we return to the subject of the interruptor disc I'm unclear how this actually improved the frequency response of a tardy selenium cell.

Or am I misunderstanding the description on p154 of Wireless World and Radio Review?

After scanning the image with the normal Nipkow disc the resulting optical 'signal' is then commutated (or as we might say analogue sampled) at a high frequency.
This is then presented to the sluggish selenium cell.

Surely the cell will respond to the mean signal?
It will still have a slow rise and fall time.
You won't have improved the frequency response by chopping the optical signal, just reduced its amplitude by the duty cycle of the interruptor disc.

If you want to amplitude modualte the signal and move the spectrum upwards you need to interrupt the actual electrical signal, not the optical signal.

If the response time of the cell were negligible then I agree the two processes would be interchangeable.

Confused of Billericay,

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Postby gary » Fri Apr 26, 2013 7:33 pm

AncientBrit wrote:
Or am I misunderstanding the description on p154 of Wireless World and Radio Review?


I haven't seen that (I don't think) so I can't comment.

AncientBrit wrote:After scanning the image with the normal Nipkow disc the resulting optical 'signal' is then commutated (or as we might say analogue sampled) at a high frequency.
This is then presented to the sluggish selenium cell.

Surely the cell will respond to the mean signal?


Indeed, and if it didn't the method wouldn't work (see below).

AncientBrit wrote:It will still have a slow rise and fall time.
You won't have improved the frequency response by chopping the optical signal, just reduced its amplitude by the duty cycle of the interruptor disc.


I disagree - keep in mind that the chopping is done at a very high frequency at a constant rate - this is pulse code modulation (a form of amplitude modulation) given a high enough rate (at least 2fmax) the original signal can be completely reconstituted - I wonder if Baird implemented a sample and hold as well?

AncientBrit wrote:If you want to amplitude modualte the signal and move the spectrum upwards you need to interrupt the actual electrical signal, not the optical signal.
Graham


ALL other things being equal (i.e. a perfect detector) you would not be able to distinguish the difference between modulating the light signal and modulating the electrical signal.

AncientBrit wrote:If the response time of the cell were negligible then I agree the two processes would be interchangeable.
Graham


Oh I see we agree on that. Yes the ultimate signal would still have a poor response except for the next trick - now I have never done this to check how well it works but it *seems* plausible but apparently Baird then takes the modulated signal and feeds it into the primary of a transformer - the secondary then carries the first derivative of the original signal. This is then mixed back together to "correct" for the poor response. Because of the high rate of "sampling" each derivative will be related to the beginning and end of the sample - it's just a form of "peaking" - how well it worked well, maybe Harry will show us... ;-)

Well that is my understanding of the principle as the literature (that I have read).
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