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G8MNY > TECHNI 22.03.18 09:07l 129 Lines 5078 Bytes #999 (0) @ WW
BID : 13393_GB7CIP
Read: GAST
Subj: Odd Resistance Finder
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Sent: 180322/0736Z @:GB7CIP.#32.GBR.EURO #:13393 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY
(Updated Nov 07)
Resistors normally come in 2 ranges, E12 has 12 resistors evenly spaced per
decade about 20% to the adjacent value, & E24 has 24 & includes the E12 series
giving value at about 10% apart. As tolerances improve there are also E24 &
E48 values available!
E12 1.0 1.2 1.5 1.8 2.2 2.7 3.3 3.9 4.7 5.6 6.8 8.2
E24 + 1.1 + 1.3 + 1.6 + 2.0 + 2.4 + 3.0 + 3.6 + 4.3 + 5.1 + 6.2 + 7.5 + 9.1
Here is a useful list of 128 values obtained with two E12 resistors.
Multiply or Divide by 10s for the range needed.
Wanted How Wanted How
E12 1000 3400 6k8//6k8, 1k2+2k2
1020 1k2//6k8 3590 5k6//10k
1031 1k5//3k3 E24 3600 1k8+1k8
1047 1k2//8k2 3700 1k+2k7, 1k5+2k2
1071 1k2//10k 3717 6k8//8k2
1080 1k8//2k7 E12 3900 1k2+2k7
1083 1k5//3k9 4000 1k8+2k2
E24 1100 2k2//2k2, 1k+100 4048 6k8//10k
1137 1k5//4k7 4100 8k2//8k2
1165 1k8//3k3 4200 1k5+2k7
1182 1k5//5k6 E24 4300 1k+3k3
E12 1200 4400 2k2+2k2
1212 2k2//2k7 4500 1k2+3k3
1229 1k5//6k8 4505 8k2//10k
1232 1k8//3k3 E12 4700
1269 1k5//8k2 4800 1k6+3k3
E24 1300 4900 1k+3k9, 2k2+2k7
1301 1k8//4k7 5000 10k//10k
1304 1k5//10k E24 5100 1k2+3k9, 1k8+3k3
1320 2k2//3k3 5400 1k5+3k9, 2k7+2k7
1350 2k7//2k7 5455 10k//12k
1362 1k8//5k6 5500 2k2+3k3
1406 2k2//3k9 E12 5600
1423 1k8//6k8 5700 1k+4k7, 1k8+3k9
1476 1k8//8k2 5900 1k2+4k7
1485 2k7//3k3 6000 12k//12k, 10k//15k, 2k7+3k
1497 2k2//4k7 6100 2k2+3k9
E12 1500 E24 6200 1k5+4k7
1525 1k8//10k 6429 10k//18k
1580 2k2//5k6 6500 1k8+4k7
1596 2k7//3k9 6600 1k+5k6, 2k7+3k9, 3k3+3k3
E24 1600 6667 12k//15k
1650 3k3//3k3 E12 6800 1k2+5k6
1662 2k2//6k8 6875 10k//22k
1715 2k7//4k7 6900 2k2+4k7
1735 2k2//8k2 7100 1k5+5k6
1788 3k3//3k9 7200 18k//12k, 3k3+3k9
E12 1800 7297 10k//27k
1803 2k2//10k 7400 1k8+5k6, 2k7+4k7
1822 2k7//5k6 E24 7500 15k//15k
1933 2k7//6k8 7674 10k//33k
1939 3k3//4k7 7765 12k//22k
1950 3k9//3k9 7800 1k+6k8, 2k2+5k6, 3k9+3k9
E24 2000 1k+1k 7959 10k//39k
2031 2k7//8k2 8000 1k2+6k8, 3k3+4k7
2071 3k3//5k6 8182 15k//18k
2126 2k7//10k E12 8200
2131 3k9//4k7 8246 10k//47k
E12 2200 1k+1k2 8300 1k5+6k8, 2k7+5k6
2222 3k3//6k8 8308 12k//27k
2299 3k9//5k6 8485 10k//56k
2350 4k7//4k7 8600 1k8+5k6, 3k9+4k7
2353 3k3//8k2 8718 10k//68k
E24 2400 2k2+2k2 8800 12k//33k
2479 3k9//6k8 8900 3k3+5k6
2481 3k3//10k 8913 10k//82k
2500 1k+1k5 8919 15k//22k
2555 4k7//5k6 9000 18k//18k
E12 2700 1k2+1k5 E24 9100
2779 4k7//6k8 9091 10k//100k
2800 5k6//5k6, 1k+1k8 9176 12k//39k
2806 3k9//10k 9200 1k+8k2
2988 4k7//8k2 9400 1k2+8k2, 4k7+4k7
E24 3000 1k2+1k8, 1k5+1k5 9500 2k7+6k8, 3k9+5k6
3071 5k6//6k8 9559 12k//47k
3197 4k7//10k 9643 15k//27k
3200 1k+2k2 9700 1k5+8k2
E12 3300 1k5+1k8 9882 12k//56k
3328 5k6//8k2 9900 18k//22k
// = in parallel, + = in series
Series combinations are better for high voltage.
Similar values spread the power dissipation more evenly.
So now you can replace that experimental preset value with 2 fixed value Rs.
------------------------------------------------------------------------------
From Jim VK7JH
R1 x R2
R = -------
R1 + R2
The formular can be written as:
1 1 1
--- = --- + ---
R R1 R2
Re-aranging gives:
1 1 1
--- = --- - ---
R2 R R1
Putting it in the form that you started with:
R x R1
R2 = ----------
R1 - R
R is the value you want & R1 is something higher in value.
There are tables that give the combination of prefered values to
save the calculations. I think I saw a TECH buletin....
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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