21-12-2021, 11:34 AM
I have recently taken a transformer to bits, as far as I can tell it is a EI-66 transformer with a 22mm centre limb measurement, there are 61 laminations in total with each having a thickness of 0.5mm so an area of 6.71 x 10-4 M2.
This next bit is me trying to get things correct, so a check of calcs and thinking would be appreciated.
It was a 240 Volt primary and I unwound the primary turns using the hand winder and got 1,100 turns, feeding this back into the formula from Ed rearranged for B, I got a value of 1.46.
Now if I am correct in my thinking for the frame coils I would need a voltage across them of 51.3 Volts at 100mA peak to peak, I would like the primary impedance to be around 4K5 Ohms for the valve, I worked the secondary impedance to be 513 Ohm so an 8.779 ratio on that giving me a turns ratio of 2.96:1.
Stop working in pk-pk values as pointed out by Jeffrey, 51.3 Volts Pk to Pk is 18.14 Volts rms, so a primary voltage of 18.14 x 2.96 is 53.73 Volts rms.
Going back to the formula, this time using 4.0 rather than 4.44 as I am after a sawtooth? and at 12.5 Hz frequency.
Turns = 53.73/(4.0 x 12.5 x 1.46 x 6.71 x 10-4 M2) means I need 1097 primary turns.
Secondary would be 1097 / 2.96 or 371 turns, I may increase this slightly by 1.05 to allow for losses to 390 turns on the secondary.
I am wondering if I could also treat the current similar with peak to rms when it comes to capacity, i.e. I need 100mA peak current so rms this would be 36 mA in the secondary, the primary would then be 12 mA. Or if it is better to rate the wire for the peak current, 34mA primary and 100mA secondary, or possibly somewhere in between to give some leeway.
The previous primary of 1100 turns was with 0.25 diameter wire, probably 34 awg and was quite full at that so my choice of wire could make the choice if I can go for push pull or not.
Adrian
This next bit is me trying to get things correct, so a check of calcs and thinking would be appreciated.
It was a 240 Volt primary and I unwound the primary turns using the hand winder and got 1,100 turns, feeding this back into the formula from Ed rearranged for B, I got a value of 1.46.
Now if I am correct in my thinking for the frame coils I would need a voltage across them of 51.3 Volts at 100mA peak to peak, I would like the primary impedance to be around 4K5 Ohms for the valve, I worked the secondary impedance to be 513 Ohm so an 8.779 ratio on that giving me a turns ratio of 2.96:1.
Stop working in pk-pk values as pointed out by Jeffrey, 51.3 Volts Pk to Pk is 18.14 Volts rms, so a primary voltage of 18.14 x 2.96 is 53.73 Volts rms.
Going back to the formula, this time using 4.0 rather than 4.44 as I am after a sawtooth? and at 12.5 Hz frequency.
Turns = 53.73/(4.0 x 12.5 x 1.46 x 6.71 x 10-4 M2) means I need 1097 primary turns.
Secondary would be 1097 / 2.96 or 371 turns, I may increase this slightly by 1.05 to allow for losses to 390 turns on the secondary.
I am wondering if I could also treat the current similar with peak to rms when it comes to capacity, i.e. I need 100mA peak current so rms this would be 36 mA in the secondary, the primary would then be 12 mA. Or if it is better to rate the wire for the peak current, 34mA primary and 100mA secondary, or possibly somewhere in between to give some leeway.
The previous primary of 1100 turns was with 0.25 diameter wire, probably 34 awg and was quite full at that so my choice of wire could make the choice if I can go for push pull or not.
Adrian
Learning as I go!
Youtube EF91 Valve
Youtube EF91 Valve
