COILS, INDUCTION


 
Coils Induction No. 1

Two windings of 1 Ohm (silk covered copper wire of 25 mils) and 25 Ohms (11 mils).  The cores are a 9/32 inch bundle, No. 24 S.W.G. well annealed, charcoal iron, left black from the annealing process to prevent eddy currents.

Used on local battery circuits.

Superseded by Coil, Induction No.12.

The National Telephone Company also produced a similar Induction Coil with the 1 ohm winding of 20.5 mils and the 25 ohm winding of 10.75 mils.  The core was a bundle of 22 mil wire of 5/16" diameter each.

Making a Coil No.1 or No.12
Coil former end pieces 1 inch square x 3/8 inch thick.
Coil former 1 3/4 inches long (2 inches would be better) x 1/2 inch diameter cardboard.
Primary winding 400 turns of 22 AWG (23 SWG) enamelled copper wire - 1 ohm.
Secondary winding 1100 turns of 30 (33 SWG) AWG enamelled copper wire - 25 ohms.
Core - 24 AWG (0.5mm) soft iron wire (All wire can be purchased from https://www.wires.co.uk/).
 

 
Coils Induction No. 2

Two windings of 1 Ohm (silk covered copper wire of 25 mils) and 150 Ohms (7 mils).  The cores are a 9/32 inch bundle, No. 24 S.W.G. well annealed, charcoal iron, left black from the annealing process to prevent eddy currents.

Used on switchboards on local battery circuits.
 

Coils Induction No. 3

Two winding coil with soldered tags.

Inner winding 26 Ohms (tags 3 and 4) and outer winding 17 Ohms (tags 1 and 2).

Superseded by Coil, Induction No. 14.

Coils Induction No. 4

Two winding coil - self connecting type.

Inner winding 26 Ohms (tags 3 & 4) and outer winding 17 Ohms (tags 1 & 2).

Superseded by Coil, Induction No. 14.

Coils Induction No. 5

Coil used for vacuum protector testing.

Primary - 0.15 Ohms.
Secondary - 350 Ohms.

With trembler break and 0.02uf condenser.
 

 
Coils Induction No. 6

Rectangular in construction and used on Operators C.B. systems.

Coil
Primary - 11 ohms (tags 5 & 6).
1st Secondary - 58 ohms (tags 3 & 4).
2nd Secondary - 240 ohms (tags 5 & 6).

Dimensions of base are 7.1 in x 2 in.
 

 
Coils Induction No. 7

Two windings of 17 Ohms and 26 Ohms.

Used on Supervisors Circuits.
 

Coils Induction No. 8

Two induction coils on a brass frame with black rectangular metal cover.  8 tags.

1st coil - Primary 18 Ohms and secondary 130 Ohms.

2nd coil - Primary 18 Ohms and secondary 130 Ohms with a non-induction in series of 360 ohms.

Operators circuit on CB No. 1 exchanges.

Supersedes Coil, Induction No.11.

Coils Induction No. 9

Two winding coil with black cover.

Primary 17 Ohms (tags 1 & 2) and secondary 26 Ohms (tags 3 & 4).

Used on Supervisors Circuits on CB No. 1 exchanges.

Mounts on Drilling No. 92.

Coils Induction No. 10

Two windings coil used on Telephone No. 44.

Primary 1.7 Ohms and secondary 75 Ohms.


Coils Induction No. 11

Two induction coils on a brass frame with metal cover.  5 tags.

1st coil - Primary 18 Ohms and secondary 130 Ohms.

2nd coil - Primary 18 Ohms and secondary 130 Ohms with a non-induction in series of 360 ohms.

Operators circuit on CB No. 1 exchanges.

Superseded by Coil, Induction No. 8.


Coils Induction No. 12

Two windings coil with soldered tags.

Primary 1 Ohm (tags 1 & 2) and secondary 25 Ohms (tags 3 & 4).

Standard for L.B. system telephone and switchboards.

Superseded Coils Induction No. 1 or NT No. 12.

Making a Coil No.1 or No.12
Coil former end pieces 1 inch square x 3/8 inch thick.
Coil former 1 3/4 inches long (2 inches would be better) x 1/2 inch diameter cardboard.
Primary winding 400 turns of 22 AWG (23 SWG) enamelled copper wire - 1 ohm.
Secondary winding 1100 turns of 30 (33 SWG) AWG enamelled copper wire - 25 ohms.
Core - 24 AWG (0.5mm) soft iron wire (All wire can be purchased from https://www.wires.co.uk/).
 

Coils Induction No. 13
 
Coils Induction No. 14

Two windings of 26 Ohms (1400 turns) (tags 3 & 4) and 17 Ohms (1700 turns) (tags 1 & 2).

Superseded Coils Induction No's 3 and 4.

Making a Coil No.14
Coil former end pieces 1 3/8 inch square x 3/8 inch thick.
Coil former 3 1/2 inches long x 1/2 inch diameter cardboard (4 1/4 inches overall including ends).
Primary winding 1700 turns of 28 AWG (30 SWG) enamelled copper wire - 17 ohms.
Secondary winding 1400 turns of 30 AWG (33 SWG) enamelled copper wire - 27 ohms.
Core - 24 AWG (0.5mm) soft iron wire (All wire can be purchased from https://www.wires.co.uk/).
 


 
Coils Induction No. 15

Three winding coil with 6 tags.

Primary 1 Ohm (tags 1 & 2), 1st secondary 19 Ohms (tags 3 & 4) and second secondary of 38 ohms (tags 5 & 6).

Used in the Bellset No. 21
 


 
Coils Induction No. 16

Three winding coil with 6 tags.

Primary 4 Ohm, 1st secondary 20 Ohms and second secondary of 440 ohms.

Used on operators telephone circuits on C.B. switchboards.
 

 
Coils Induction No. 18

Two windings of 17 Ohms (1700 turns) (tags 1 & 2) and 33 Ohms (1400 turns) (tags 3 & 4).

Used with Anti-sidetone Transformer No. 35A.


 
Coils Induction No. 20

Three windings of 30 Ohms (1600 turns) (tags 4 & 5), 200 Ohms (1580 turns) (tags 3 & 5) and 44 Ohms (2400 turns) (tags 1 & 2).

Also two non inductive resistances of 30 Ohms (tags 3 & 6) and 85 Ohms (tags 2 & 5).

Coils Induction No. 21

Three windings of 1 Ohm (400 turns) (tags 1 & 2), 17 Ohms (1000 turns) (tags 3 & 4) and 33 Ohms (1500 turns) (tags 5 & 6).

Used on Telephone No's 250 & 251 and the Bellset No. 37.

No. 21A was a No. 21 complete with two mounting brackets.

In Australia some 300 series magneto phones used the No. 21A as follows (no winding details):-
1 Ohm between tags 1 & 2 .
17 Ohms between tags 3 & 4.
33 Ohms + 900 Ohms NI between tags 5 & 6
tags 3 & 5 linked.

Specification - D980
Drawing - 9875
.


 
Coils Induction No. 22

Three windings of 50 Ohms (tags 3 & 4), 215 Ohms (tags 3 & 6) and 17 Ohms (tags 1 & 2).

Also has two non-inductive resistances of 150 Ohms (tags 3 & 7) and 400 Ohms (tags 3 & 5).
 

 
Coils Induction No. 22 Mark 2

Three windings of 54 Ohms (1600 turns) (tags 3 & 4), 415 Ohms (2000 turns) with 150 Ohm NI resistance in series (tags 3 & 5) and 17 Ohms (2000 turns) (tags 1 & 2).

Also has three non-inductive resistances of 150 Ohms (tags 3 & 5 with 415 Ohm winding in series), 50 Ohms (tags 5 & 6) and 150 Ohms (tags 3 & 7).

Coils Induction No. 23

Three windings of 44 Ohms (tags 1 & 2), 30 Ohms (tags 4 & 5) and 200 Ohms (tags 3 & 5). A NI resistor of 85 Ohms is between tags 2 and 5.
 

 
Coils Induction No. 24

Three windings of 83 Ohms (1600 turns) (tags 3 & 4), 550 Ohms (2000  turns) (tags 3 & 5) and 21 Ohms (2000 turns) (tags 1 & 2).

Also has two non inductive resistances of 50 Ohms (tags 5 & 6) and 150 Ohms (tags 3 and 7).

Coils Induction No. 25

Two windings of 25 Ohms (tags 3 & 4) and 1 Ohm (tags 1 & 2).

Coils Induction No. 27

Five windings of 35 Ohms (2600 turns) (tags 1 & 2), 75 Ohms (1800 turns) (tags 3 & 4), 30 Ohms (800 turns) (tags 3 & 5).

Also has two non-inductive resistances of 30 Ohms (tags 5 & 6) and 30 Ohms (tags 3 & 7).


 
Coils Induction No. 29

Two windings of 36 Ohms (600 turns) (tags 2 & 3) and 135 Ohms (2700 turns) (tags 1 & 2).

Used on Telephone No. 280.
 

 
Coils Induction No. 30

Three windings of 15 Ohms (1220 turns), 10.5 Ohms (666 turns) and 7.5 Ohms (420 turns).

Used on the Telephone No. 700.

 

Coils Induction No. 31

Three windings of 6 Ohms (315 turns) (tags 2 & 3), 8 Ohms (540 turns) (tags 1 & 2) and 22 Ohms (900 turns) (tags 4 & 5).

Used on Telephone No's 706, 710 and 711.

Coil Induction No. 32

Three windings of 7 Ohms (235 turns) (tags 2 & 3), 11 Ohms (402 turns) (tags 1 & 2) and 23 Ohms (670 turns) (tags 4 & 5).

 
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Last revised: July 28, 2020

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