I just measured the 1640SE primary inductance (without DC) with different gap spacers (plastic), all with firm pressure on the I laminations:
original spacer 0.2 mm 27.646 Hy, DC Imax = 200 mA
0.1 mm spacer 30.77 Hy , DC I max = 180 mA
0.075 mm spacer 33.25 Hy, DC Imax = 166 mA
0.050 mm spacer 37.62 Hy, DC Imax = 147 mA
0.025 mm spacer 42.4 Hy, DC Imax = 130 mA
no spacer 47.66 Hy, DC Imax = 116 mA
I can adjust primary L (and inversely DC Imax) now using this table. So I can fit the SE OT to the tube now.
Actual Lpri, with full Imax DC applied, will give 1/2 the Lpri measured above.
Looking at the latest Hammond 1627SEA (2500 Ohm Zpri, 160 mA DC Imax), 20 Hys in Hammond's table, 2x that ( 40 Hy ) when measured without DC applied, would indicate a 0.0375 mm spacer for the 1640SE to duplicate it for Lpri, but a 0.067 mm spacer to get the 160 mA DC Imax. Not quite as optimized as the 1627SEA for 2500 Ohm Zpri, but not bad.
original spacer 0.2 mm 27.646 Hy, DC Imax = 200 mA
0.1 mm spacer 30.77 Hy , DC I max = 180 mA
0.075 mm spacer 33.25 Hy, DC Imax = 166 mA
0.050 mm spacer 37.62 Hy, DC Imax = 147 mA
0.025 mm spacer 42.4 Hy, DC Imax = 130 mA
no spacer 47.66 Hy, DC Imax = 116 mA
I can adjust primary L (and inversely DC Imax) now using this table. So I can fit the SE OT to the tube now.
Actual Lpri, with full Imax DC applied, will give 1/2 the Lpri measured above.
Looking at the latest Hammond 1627SEA (2500 Ohm Zpri, 160 mA DC Imax), 20 Hys in Hammond's table, 2x that ( 40 Hy ) when measured without DC applied, would indicate a 0.0375 mm spacer for the 1640SE to duplicate it for Lpri, but a 0.067 mm spacer to get the 160 mA DC Imax. Not quite as optimized as the 1627SEA for 2500 Ohm Zpri, but not bad.
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Woops! For the same core and magnetic material, NxI stays constant, not L x I. (N is turns, so SQRT(L) x I stays constant ) So my calculated DC Imax numbers in the above table need fixing, as below:
1640SE:
original spacer 0.2 mm 27.646 Hy (no DC), DC Imax = 200 mA
0.1 mm spacer 30.77 Hy , DC I max = 189.6 mA
0.075 mm spacer 33.25 Hy, DC Imax = 182.3 mA
0.050 mm spacer 37.62 Hy, DC Imax = 171,4 mA
0.025 mm spacer 42.4 Hy, DC Imax = 161.5 mA
no spacer 47.66 Hy, DC Imax = 152.3 mA
1627SEA
40 Hy (no DC) and 160 mA DC Imax
So one can get the same L and DC Imax figures as the Hammond 1627SEA by just changing the gap on the 1640SE.
What does not work so well is the rated power. Going from the 1627SEA to a 1640SE you only get 0.707 as much current or 0.707 as much voltage going the other way. (for the same copper heat loss or saturation magnetics) So 71% of the power rating (at the LF end). (but since the SEA versions got uprated to 30 Watts from the previous 25 Watts, that would be 85% of original 25 W power, ie 21 W, at the LF end )
So the original gap spaced 1640SE would be good for two 30 Watt Sweep tubes in parallel (1250 Ohm OT), or with a gap change to 0.025 mm should work quite well for a single 30 Watt Sweep tube. (used as a 2500 Ohm OT)
1640SE:
original spacer 0.2 mm 27.646 Hy (no DC), DC Imax = 200 mA
0.1 mm spacer 30.77 Hy , DC I max = 189.6 mA
0.075 mm spacer 33.25 Hy, DC Imax = 182.3 mA
0.050 mm spacer 37.62 Hy, DC Imax = 171,4 mA
0.025 mm spacer 42.4 Hy, DC Imax = 161.5 mA
no spacer 47.66 Hy, DC Imax = 152.3 mA
1627SEA
40 Hy (no DC) and 160 mA DC Imax
So one can get the same L and DC Imax figures as the Hammond 1627SEA by just changing the gap on the 1640SE.
What does not work so well is the rated power. Going from the 1627SEA to a 1640SE you only get 0.707 as much current or 0.707 as much voltage going the other way. (for the same copper heat loss or saturation magnetics) So 71% of the power rating (at the LF end). (but since the SEA versions got uprated to 30 Watts from the previous 25 Watts, that would be 85% of original 25 W power, ie 21 W, at the LF end )
So the original gap spaced 1640SE would be good for two 30 Watt Sweep tubes in parallel (1250 Ohm OT), or with a gap change to 0.025 mm should work quite well for a single 30 Watt Sweep tube. (used as a 2500 Ohm OT)
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Double Woops!!!
Looks like the 1st table (post # 41 ) IS correct for impedance shifting a SE OT by Gap Changing. The effective material permeability IS changing with the different gapping. With permeability change, but the same number of turns, the DC Imax has to change inversely with the permeability change to keep the same 50% DC flux. So for DC current, L x Imax DC stays constant. So 1st table, post #41 applies.
For impedance shifting by optimum # turns winding (ie, different, correct OT model ), the turns increase as the SQRT of impedance. L or Z increases as the turns squared, the usual formula. But there is no effective permeabilty change, same gap. So the DC Imax decreases as the SQRT of impedance or L. So SQRT(L) x Imax DC stays constant. L and Z vary proportionately. So 2nd table, post #42 applies.
Inductance L sets the AC flux density and AC power , and Imax DC sets the DC flux density.
For re-gapping to change the primary impedance, one has to compromise on these using the 1st table. Which will result in less power rating (at the LF end) Looks like reducing the gap to 1/8 of the original gives a good compromise. (the fringing fields around the air gap effectively make the gap width changes non-linear, a lot of magn. flux leaks around the spacer )
Looks like the 1st table (post # 41 ) IS correct for impedance shifting a SE OT by Gap Changing. The effective material permeability IS changing with the different gapping. With permeability change, but the same number of turns, the DC Imax has to change inversely with the permeability change to keep the same 50% DC flux. So for DC current, L x Imax DC stays constant. So 1st table, post #41 applies.
For impedance shifting by optimum # turns winding (ie, different, correct OT model ), the turns increase as the SQRT of impedance. L or Z increases as the turns squared, the usual formula. But there is no effective permeabilty change, same gap. So the DC Imax decreases as the SQRT of impedance or L. So SQRT(L) x Imax DC stays constant. L and Z vary proportionately. So 2nd table, post #42 applies.
Inductance L sets the AC flux density and AC power , and Imax DC sets the DC flux density.
For re-gapping to change the primary impedance, one has to compromise on these using the 1st table. Which will result in less power rating (at the LF end) Looks like reducing the gap to 1/8 of the original gives a good compromise. (the fringing fields around the air gap effectively make the gap width changes non-linear, a lot of magn. flux leaks around the spacer )
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