11-12-2021, 08:29 PM
Hello all, today has been spent dealing with general family matters so not had much time to think on this lot today. I must get to sleep before midnight this evening.
Long post very sorry.
I was reading some downloads this morning and as Ed has mentioned turns out it is using Imperial measurements for all core sizes and talks about flux density in lines per square inch, stacking factors of 0.92 for 1 x 1 interleave and 0.95 for a butt stack. I would have thought it should be the other way round with interleave at 0.95 but no matter The downloads were Wolpert Power transformers and audio transformers. I did not get to far before I gave up for sleep.
I bought a job lot of transformers from Ebay some time ago, and where I can, I strip them down for the laminations it does unfortunately mean I do not know the core material details, or what VA the transformers were as they are not marked as 12 Volt 500ma etc.So any home wound transformers have been a finger in the air approach.
The transformer I wound for the Line scan, which has a frequency of 400Hz, I calculated last night had a core section of 6 x 10-4 m2.
when I made it up it was all just guessing but used some figure I had written down for an audio transformer. I used 14 turns per volt, a butt stack with a piece of high temp tape as an air core as there was a DC bias current flowing as well as the scan.
This could well have been over the top, I know I am lacking how to work this out better.
I have also bean using peak to peak measurements when trying to work things out dealing with the sawtooth waveform and as jeffrey pointed out the rms values would be a lot less.
For example the line scan coils when driven with DC just needed 12.5 volts to get full deflection, the tester said the coils inductance was only 61.6mH so a little more maths and calculated the scan voltage should only be 13.7 Volts call it 14 Volts peak to peak. So I picked 14 Volts for the secondary.
I needed a peak current of 204 mA to drive the spot from one side to the other and using a EL84 I wanted to drop this to a more manageable figure for the anode current so used an 8.8:1 ratio, so the primary current should be in the region of 24 mA plus DC.
so with these figure the primary voltage peak to peak would be around 123 Volts so with the 14 TPV I used 1724 turns for primary and 196 turns for secondary, I just guessed I would be OK, it does work, in a fashion. The average current flowing through the anode is 24.2mA as I monitored the voltage drop on a 100 Ohm resistor last night, so I believe that the line scan coils and transformer are supplying some current back into the system just after flyback, fly back is massive so I have very heavily damped the primary side of the transformer using caps and resistors.
I am not sure how some of the issues would be reduced if rather than 123 and 14 Volts, I used 43.5 and 5 volts being rms for the windings in the transformer. A previous comment from Jeffrey, leads me to believe not a lot as the inductance of the transformer has little effect it all being from the scan coils and the square of the turns ratio, which I was able to understand.
During the measurements i also found that the actual peak to peal scan voltage on the coils was 28 Volts and not 14, the primary scan voltage peak to peak voltage is 230 Volts rather than 123 Volts, so I know I could have some errors with adding a few extra turns on the secondary, but for the voltages to be nearly double what I worked out get me wondering what else i have missed.
I would like to do the frame scan using a push pull ECC82 as again suggested by Jeffrey, but I need to understand what size core is needed at 12.5 Hz. Testing with DC the resistance of the scan coils are 511 Ohms, the frequency and inductance of the coils means at 12.5 Hz, 50 Volts peak to peak would do a full scan, So 18 Volts as Jeffrey posted at 511 Ohms is only 0.634 watts. But before I go any further I could do with understanding why the line scan is double the voltages of the DC tests?
It will be Monday or Tuesday before I can lift a soldering iron as I have a few other items to sort out.
War and peace over with.
Stay safe.
Adrian
Long post very sorry.
I was reading some downloads this morning and as Ed has mentioned turns out it is using Imperial measurements for all core sizes and talks about flux density in lines per square inch, stacking factors of 0.92 for 1 x 1 interleave and 0.95 for a butt stack. I would have thought it should be the other way round with interleave at 0.95 but no matter The downloads were Wolpert Power transformers and audio transformers. I did not get to far before I gave up for sleep.
I bought a job lot of transformers from Ebay some time ago, and where I can, I strip them down for the laminations it does unfortunately mean I do not know the core material details, or what VA the transformers were as they are not marked as 12 Volt 500ma etc.So any home wound transformers have been a finger in the air approach.
The transformer I wound for the Line scan, which has a frequency of 400Hz, I calculated last night had a core section of 6 x 10-4 m2.
when I made it up it was all just guessing but used some figure I had written down for an audio transformer. I used 14 turns per volt, a butt stack with a piece of high temp tape as an air core as there was a DC bias current flowing as well as the scan.
This could well have been over the top, I know I am lacking how to work this out better.
I have also bean using peak to peak measurements when trying to work things out dealing with the sawtooth waveform and as jeffrey pointed out the rms values would be a lot less.
For example the line scan coils when driven with DC just needed 12.5 volts to get full deflection, the tester said the coils inductance was only 61.6mH so a little more maths and calculated the scan voltage should only be 13.7 Volts call it 14 Volts peak to peak. So I picked 14 Volts for the secondary.
I needed a peak current of 204 mA to drive the spot from one side to the other and using a EL84 I wanted to drop this to a more manageable figure for the anode current so used an 8.8:1 ratio, so the primary current should be in the region of 24 mA plus DC.
so with these figure the primary voltage peak to peak would be around 123 Volts so with the 14 TPV I used 1724 turns for primary and 196 turns for secondary, I just guessed I would be OK, it does work, in a fashion. The average current flowing through the anode is 24.2mA as I monitored the voltage drop on a 100 Ohm resistor last night, so I believe that the line scan coils and transformer are supplying some current back into the system just after flyback, fly back is massive so I have very heavily damped the primary side of the transformer using caps and resistors.
I am not sure how some of the issues would be reduced if rather than 123 and 14 Volts, I used 43.5 and 5 volts being rms for the windings in the transformer. A previous comment from Jeffrey, leads me to believe not a lot as the inductance of the transformer has little effect it all being from the scan coils and the square of the turns ratio, which I was able to understand.
During the measurements i also found that the actual peak to peal scan voltage on the coils was 28 Volts and not 14, the primary scan voltage peak to peak voltage is 230 Volts rather than 123 Volts, so I know I could have some errors with adding a few extra turns on the secondary, but for the voltages to be nearly double what I worked out get me wondering what else i have missed.
I would like to do the frame scan using a push pull ECC82 as again suggested by Jeffrey, but I need to understand what size core is needed at 12.5 Hz. Testing with DC the resistance of the scan coils are 511 Ohms, the frequency and inductance of the coils means at 12.5 Hz, 50 Volts peak to peak would do a full scan, So 18 Volts as Jeffrey posted at 511 Ohms is only 0.634 watts. But before I go any further I could do with understanding why the line scan is double the voltages of the DC tests?
It will be Monday or Tuesday before I can lift a soldering iron as I have a few other items to sort out.
War and peace over with.
Stay safe.
Adrian
Learning as I go!
Youtube EF91 Valve
Youtube EF91 Valve
